Energy storage systems for load handling equipment.

Abstract

The present invention relates to a load handling apparatus (30) for lifting and moving one or more stacked containers (10) within a storage system comprising a grid framework (14) supporting a path arranged in a grid pattern above a stack (12) of containers (10), the load handling apparatus (30) comprising: i. a body (32) housing a drive mechanism operatively arranged to move the load handling apparatus (30) on the grid framework (14); and ii. a lifting drive assembly and a grabber device (39) configured, in use, to releasably grasp a container (10) and lift the container (10) from the stack (12) into a container receiving space (40), wherein: a rechargeable power source (100); and iv. an assembly of one or more supercapacitor modules (102); wherein the lifting drive assembly (10) and / or drive mechanism comprises at least one motor forming an electrical load (104); wherein the electrical load (104) is connected across the assembly of one or more supercapacitor modules (102), and the rechargeable power source 100 is connected in parallel to the assembly of one or more supercapacitor modules (102) so as to provide power to the assembly of one or more supercapacitor modules (102).

Description

[Technical field]

[0001] The present invention relates to the field of load handling equipment for handling storage containers or bins in a store comprising a grid of stacked containers, and more particularly to an energy storage system for a load handling equipment. [Background technology]

[0002] Storage systems comprising a three-dimensional storage grid structure in which storage containers / bins are stacked on top of each other are well known. PCT Publication WO 2015 / 185628 (Ocado) describes a known storage and fulfillment system in which a stack of ten bins or containers is arranged within the grid framework structure. The bins or containers are accessed by a load handling device operable on a truck located on top of the grid framework. This type of system is shown diagrammatically in Figures 1 to 3 of the accompanying drawings. As shown in Figures 1 and 2, stackable containers known as bins 10 are stacked on top of each other to form a stack 12. The stack 12 is arranged within a grid framework structure 14 within a warehouse or manufacturing environment. The grid framework is made up of a number of storage or grid rows. Each grid within the grid framework structure has at least one grid row for storage of a stack of containers. Figure 1 is a schematic perspective view of the grid framework structure 14 and Figure 2 is a top view showing a stack 12 of bins 10 arranged within the framework structure 14. Each bin 10 typically holds multiple product items (not shown), which may be the same or may be of different product types depending on the application. The grid framework structure 14 comprises a plurality of upright members 16 supporting horizontal members 18, 20. A first set of parallel horizontal members 18 are vertically arranged 25 on a second set of parallel horizontal members 20 to form a plurality of horizontal grid structures comprising a plurality of grid cells 23 supported by the upright members 16. The members 16, 18, 20 are typically fabricated from metal. The bins 10 are stacked within the grid cells 23 between the members 16, 18, 20 of the grid framework structure 14 such that the grid framework structure 14 prevents horizontal movement of the stack 12 of bins 10 and guides vertical movement of the bins 10.

[0003] The upper level of the grid framework structure 14 includes rails 22 arranged in a grid pattern with a plurality of grid cells 23 across the top of the stacks 12. With further reference to FIG. 3 , the rails 22 support a plurality of load handling apparatuses 30. A first set 22a of parallel rails 22 guides movement of the robotic load handling apparatus 30 in a first direction (e.g., X direction) across the top of the grid framework structure 14, and a second set 22b of parallel rails 22 arranged perpendicular to the first set 22a guides movement of the load handling apparatus 30 in a second direction (e.g., Y direction) perpendicular to the first direction. In this manner, the rails 22 allow movement of the robotic load handling apparatus 30 laterally in two dimensions in the horizontal XY plane such that the load handling apparatus 30 may be moved into position above any of the stacks 12. The known load handling apparatus 30 shown in Figures 4 and 5 comprises a vehicle body 32 as described in PCT Patent Publication WO 2015 / 019055 (Ocado), incorporated herein by reference, where each load handling apparatus 30 covers only one grid space or grid cell 23 of a grid framework structure 14. Here, the load handling apparatus 30 comprises a wheel assembly comprising a first set of wheels 34 consisting of a pair of wheels at the front of the vehicle body 32 and a pair of wheels 34 at the rear of the vehicle 32 for engaging a first set of rails or tracks to guide movement of the device in a first direction, and a second set of wheels 36 consisting of a pair of wheels 36 on each side of the vehicle 32 for engaging a second set of rails or tracks to guide movement of the device in a second direction. Each of the sets of wheels is driven by one or more motors to enable movement of the vehicle in the X and Y directions respectively along the rails. One or both sets of wheels can be moved vertically to lift each set of wheels off of its respective rails, thereby allowing the vehicle to move in a desired direction.

[0004] While Figures 4 and 5 show a load handling apparatus in which the container receiving space occupies a single grid space that is a recess within the vehicle body, the invention also encompasses load handling apparatus that include a cantilever as part of the vehicle body, in which case the container receiving space is located below the cantilever arm.

[0005] The load handling apparatus 30 is equipped with a lifting device or crane mechanism driven by one or more motors for lifting the storage container from above, which may weigh up to 30 kg. The crane mechanism comprises a winch tether or cable 38 wound on a spool or reel (not shown) and a grabber device 39. The lifting device comprises a set of lifting tethers 38 extending vertically and connected near or to four corners of a lifting frame 39, otherwise known as a grabber device (one tether near each of the four corners of the grabber device), for releasable connection with the storage container 10. The grabber device 39 is configured to releasably grip the top of the storage container 10 for lifting it from a stack of containers in a storage system of the type shown in Figures 1 and 2.

[0006] The wheels 34, 36 are positioned around the periphery of a cavity or recess known as a container-receiving recess 40 in the lower portion. The recess is sized to accommodate the container 10 when it is lifted by the crane mechanism, as shown in Figures 5a and 5b. When the container is in the recess, it is lifted off the lower rails, allowing the vehicle to move laterally to a different location. Upon reaching the target location, for example an access point in another stack, storage system, or conveyor belt, the bin or container can be lowered from the container-receiving portion and released from the grabber device.

[0007] Although not shown in Figures 1-3, the load handling apparatus 30 is powered during operation by an on-board rechargeable power source. One common type of rechargeable power source is a battery. Examples of rechargeable batteries are lithium ion batteries, nickel cadmium batteries, nickel metal hydride batteries, lithium ion polymer batteries, thin film batteries, and Smart battery Carbon Foam-based Lead Acid batteries.

[0008] Batteries have the technical advantage of high energy density, i.e., high capacity to store energy per unit mass, making them suitable for use in mobile applications such as load handling equipment, since they store enough energy to power devices for extended periods between charges. Batteries have a lower self-discharge rate, so they can hold enough charge to continue operating after periods of downtime. However, batteries have a low power density, making them unsuitable for handling high acceleration demands and limited in the amount of regenerative energy they can capture from deceleration. Also, power losses due to resistance in the battery mean that excessive battery cycling converts some electrical energy into heat, which, along with wasting energy, can be problematic in low temperature environments.

[0009] Other disadvantages of batteries are that they are heavy, expensive, suffer from resistive power losses, have long charging times, have a limited lifespan of charge / discharge cycles, and degrade over time with use. A slow charging rate means that operating time is lost while the battery is charging. A limited number of charge / discharge cycles means that the battery has a short lifespan and requires frequent replacement.

[0010] An alternative to battery technology is the supercapacitor. Supercapacitors have a high power density, which makes them suitable for applications with high acceleration demands (high power draw for short periods of time) and can also capture renewable energy from deceleration events (high power input for short periods of time). The advantages of supercapacitors over batteries are that they are lighter, cheaper, more efficient, charge faster, and can undergo more charge / discharge cycles with less degradation over time. Faster charging means less downtime. The main disadvantages of supercapacitors compared to batteries are that they have a high self-discharge rate (so they cannot hold enough charge to keep working after periods of inactivity) and have a lower energy density.

[0011] Figure 6 is a Ragone plot of power density versus energy density, showing the relative positions of different types of energy storage devices. From this blot, it can be seen that supercapacitors (labeled as EDLC, electric double layer capacitor in Figure 6) have low energy density but higher power density, while lithium ion batteries have relatively higher energy density and lower power density.

[0012] Table 1 compares some of the properties of the battery and the supercapacitor.

[0013] [Table 1]

[0014] Prior art load handling equipment (e.g., as described in PCT Patent Publication WO 2015 / 019055), while having the advantage of high energy density, suffers from all of the problems associated with rechargeable batteries as described above.

[0015] WO2020169474A1 (AutoStore) discloses a container handling vehicle powered by a first and a second rechargeable power source, in particular a rechargeable battery and a supercapacitor. These have some of the advantages of supercapacitors but still suffer from the disadvantages that the batteries degrade and energy is wasted as heat.

[0016] UK Patent No. 2006089.3 discloses a load handling device in which the primary power source is a supercapacitor and a DC-DC converter is used to vary the voltage. These have the advantages of supercapacitors as discussed above, but because the supercapacitor is the only power source, the load handling device has the disadvantages of poor energy density and high self-discharge rate.

[0017] This application claims priority from UK Patent Application No. 2006089.3, filed April 24, 2020, UK Patent No. 2010704.1, filed July 10, 2020, and UK Patent No. 2020583.7, filed December 23, 2020, the contents of which are incorporated herein by reference. Summary of the Invention

[0018] The present invention provides a load handling device for lifting and moving one or more stacked containers within a storage system comprising a grid framework supporting a pathway arranged in a grid pattern above the stack of containers, the load handling device comprising: i) a body housing a drive mechanism operatively arranged to move the load handling apparatus over the grid framework; ii) a lifting device comprising a lifting drive assembly and a grabber device configured, in use, to releasably grasp a container and lift the container from the stack into the container receiving space, wherein the lifting drive assembly and / or the drive mechanism comprises at least one motor forming an electrical load; iii) a rechargeable power source; and iv) an assembly of one or more supercapacitor modules, A load handling device, characterized in that an electrical load is connected across the one or more assemblies of supercapacitor modules, and a rechargeable power source is connected in parallel to the one or more assemblies of supercapacitor modules so as to be configured to provide power to the one or more assemblies of supercapacitor modules.

[0019] For ease of reference, the terms "assembly of one or more supercapacitor modules" and "supercapacitor" are used interchangeably in describing the present invention. When referring to a supercapacitor, it will be understood that the term encompasses an assembly of supercapacitor modules connected in series and / or parallel.

[0020] A common problem with load handling equipment, particularly those where the rechargeable power source is a rechargeable battery, is that the battery experiences frequent charge / discharge cycles from the electrical load as a result of acceleration and operation of the lifting drive assembly and / or drive mechanism. This places a heavy burden on the rechargeable battery because the internal resistance of the battery causes the battery to heat up during the charge-discharge cycles. The charge-discharge cycles can cause premature aging of the battery, necessitating more frequent battery replacement.

[0021] To overcome this problem, the rechargeable power source of the present invention is primarily used to supply charge to one or more supercapacitor modules, rather than directly providing power to the electrical load. Compared to rechargeable batteries, supercapacitors are more robust to charge-discharge cycles from electrical loads, and therefore can withstand surges in power draw during acceleration of load handling equipment on the grid. The combination of a rechargeable battery and one or more supercapacitor modules provides a hybrid system with high power density and high energy density, combining the advantages of batteries and supercapacitors. The rechargeable power source can power an assembly of one or more supercapacitor modules with a stable current, thus avoiding the damaging effects of frequent charge-discharge cycles.

[0022] An advantage of the present invention over prior art load handling devices is that the life of the rechargeable power source is extended, thus reducing operating costs and downtime.

[0023] The load handling device may further include a load DC-DC converter between the assembly of one or more supercapacitor modules and the electrical load. The load DC-DC converter between the assembly of one or more supercapacitor modules and the electrical load may be a boost converter.

[0024] The load handling device may further include a source DC-DC converter between the rechargeable power source and the assembly of one or more supercapacitor modules. The source DC-DC converter between the rechargeable power source and the assembly of one or more supercapacitor modules may be a step-down converter.

[0025] The controller may be configured to vary the power supplied from the rechargeable power source to the assembly of one or more supercapacitor modules. The controller may be configured to instruct the rechargeable power source to supply charge to the assembly of one or more supercapacitor modules when a voltage of the assembly of one or more supercapacitor modules falls below a predetermined supercapacitor target voltage threshold. The predetermined supercapacitor target voltage threshold may be lower than a maximum rated voltage of the assembly of one or more supercapacitor modules. The controller may be configured to instruct the rechargeable power source to supply charge to the assembly of one or more supercapacitor modules at a predetermined threshold current for battery balancing. The controller may be configured to disconnect the rechargeable power source from the assembly of one or more supercapacitor modules such that the rechargeable power source experiences a period of low current drain during which no charge is supplied to the assembly of one or more supercapacitor modules.

[0026] The load handling apparatus may further comprise an energy recovery circuit for transferring regenerated energy from the drive mechanism and / or the lift drive assembly to the assembly of one or more supercapacitor modules. The energy recovery circuit may comprise a diode or a transistor.

[0027] An assembly of one or more supercapacitor modules can have a lower internal resistance than a rechargeable power source.

[0028] The electrical load may comprise a first portion and a second portion, the first portion of the electrical load may comprise a kinetic power load and the second portion of the electrical load may comprise a non-kinetic power load. The rechargeable power source may be configured to provide an electrical charge to the non-kinetic power load.

[0029] The assembly of one or more supercapacitor modules may be configured as a primary power supply for the load handling equipment, and the rechargeable power source may be configured as an auxiliary power supply. The controller may be configured to direct the rechargeable power source to provide backup power to the electrical load when the voltage on the assembly of one or more supercapacitor modules falls below a predetermined supercapacitor voltage threshold.

[0030] One or more assemblies of supercapacitor modules may be distributed around the outside of a container-receiving recess within the body of the load handling device, between the outer and inner walls of the load handling device.

[0031] An assembly of one or more supercapacitor modules may comprise a capacitor, a supercapacitor, an ultracapacitor, a lithium capacitor, an electrochemical double layer capacitor, an electric double layer capacitor, a pseudocapacitor, or a hybrid capacitor.

[0032] The rechargeable power source may comprise a lithium ion battery, a lithium ion polymer battery, a lithium air battery, a lithium iron battery, a lithium iron phosphate battery, a lead acid battery, a nickel cadmium battery, a nickel metal hydride battery, a nickel zinc battery, a sodium ion battery, a sodium air battery, a thin film battery, or a smart battery carbon foam based lead acid battery.

[0033] Another aspect of the invention is a storage system comprising a grid framework supporting a pathway arranged in a grid pattern above a stack of containers and a plurality of load handling apparatuses as defined herein. The storage system may further comprise one or more supercapacitor charging stations located at grid locations above the access points, within which an assembly of one or more capacitor modules on the load handling apparatus is charged by one of the one or more supercapacitor charging stations during a lifting or lowering operation. The one or more supercapacitor charging stations may be high rate inductive supercapacitor charging stations. A controller on the load handling apparatus may be configured to command the assembly of one or more supercapacitor modules to charge the rechargeable power source. The controller may be configured to command the one or more supercapacitor modules to provide a charge to the rechargeable power source at a predetermined threshold current for battery balancing. The one or more supercapacitor charging stations may enable the load handling apparatus to maintain a voltage level of the rechargeable power source above a predetermined threshold voltage for powering an electrical load.

[0034] A further aspect of the invention is a fulfillment center comprising a storage system as described herein. The temperature inside the fulfillment center may be either an ambient temperature of 4° C. or higher, a refrigerated temperature between substantially 0° C. and substantially 4° C., or a freezer temperature between substantially −25° C. and substantially 0° C.

[0035] Connecting a supercapacitor between a rechargeable power source and an electrical load allows an energy storage system to enjoy the benefits of both high energy density and high power density while mitigating the drawbacks. This is especially true when the rechargeable power source is a high energy density battery. The supercapacitor undergoes charge / discharge cycles caused by acceleration / deceleration demands from the electrical load, protecting the battery from these cycles and thus improving battery life. Improved battery life results in reduced operating costs and reduced downtime as the batteries do not need to be replaced as frequently. Reduced battery cycles mean reduced battery energy losses and less useful energy wasted as heat. This is especially important when the load handling equipment is operating in a refrigerated or frozen goods fulfillment center, where the temperature of the fulfillment center is kept low. In this situation, not only does all the wasted heat from the load handling equipment represent a waste of energy, but more energy consumption is needed to keep the temperature of the fulfillment system low.

[0036] Additional features and aspects of the present invention will become apparent from the following detailed description of illustrative embodiments which proceeds with reference to the drawings. [Brief description of the drawings]

[0037] [Figure 1] 1 is a schematic diagram of a grid framework structure according to known systems; [Diagram 2] FIG. 2 is a schematic top view showing a stack of bins arranged within the framework structure of FIG. 1. [Diagram 3] 1 is a schematic diagram of a known system of load handling equipment operating on a grid framework structure. [Figure 4] FIG. 2 is a schematic perspective view of a load handling apparatus showing a lifting device for gripping a container from above. [Diagram 5]Figure 5(a) is a schematic cutaway perspective view of the load handling apparatus of Figure 4 showing a container receiving space of the load handling apparatus; Figure 5(b) is a schematic cutaway perspective view of the load handling apparatus of Figure 4 showing a container accommodated within the container receiving space of the load handling apparatus; [Figure 6] Ragone plot showing the energy and power densities of different energy storage devices. [Figure 7] FIG. 1 is a circuit diagram showing a rechargeable power source and a supercapacitor connected in parallel to an electrical load. [Figure 8] A circuit diagram featuring a source DCDC converter between a rechargeable power source and a supercapacitor, and a load DCDC converter between the supercapacitor and an electrical load. [Figure 9] Circuit diagram featuring step-down and step-up DC-DC converters. [Figure 10] Schematic diagram of a PID controller for a boost converter. [Figure 11] FIG. 2 is a circuit diagram featuring an energy recovery circuit for directing recovered energy into a supercapacitor. [Figure 12] 1 is a circuit diagram featuring a non-motorized power load that draws power from a rechargeable power source. [Figure 13] Schematic diagram showing the direction of current flow during a deceleration event. [Figure 14] FIG. 2 is a circuit diagram showing the direction of current flow during a deceleration event, when a rechargeable power source is charging a supercapacitor. [Figure 15] FIG. 4 is a circuit diagram showing the direction of current flow while the load handling equipment is idling. [Figure 16] FIG. 2 is a circuit diagram showing the direction of current flow while the load handling equipment is idling, with a rechargeable power source charging the supercapacitor. [Figure 17] Schematic diagram showing the direction of current flow during an acceleration event. [Figure 18] FIG. 2 is a circuit diagram showing the direction of current flow during an acceleration event, when a rechargeable power source is charging a supercapacitor. [Figure 19]FIG. 13 illustrates the transient currents caused by the lowering and raising of the grabber device when depositing and removing a storage container. [Figure 20] 1 is a schematic diagram of a load handling apparatus showing a gap between an inner wall and an outer wall of a vehicle body. [Figure 21] Schematic diagram of a load handling device showing supercapacitor modules distributed within the gap between the interior and exterior walls of the vehicle body. [Figure 22] FIG. 11 is a diagram comparing battery voltage measurements, manufacturing data, and voltage and state of charge from the battery fuel gauge. [Figure 23] FIG. 13 illustrates how battery fuel gauge readings become inaccurate after a period of continuous operation. [Figure 24] FIG. 2 is a circuit diagram showing a rechargeable power supply connected in parallel with an electrical load and a filter circuit. [Diagram 25] FIG. 2 is a circuit diagram showing a rechargeable power supply connected in parallel with an electrical load and a filter circuit, with a filter DCDC converter between the filter circuit and the electrical load. [Figure 26] FIG. 1 is a circuit diagram showing a rechargeable power supply connected in parallel with an electrical load and a filter circuit, with a filter DCDC converter between the filter circuit and the electrical load, and a source DCDC converter between the rechargeable power supply and the filter circuit. [Figure 27] Figure 27a shows an embodiment of the filter circuit that is an RC circuit, Figure 27b shows an embodiment of the filter circuit that is an RL circuit, Figure 27c shows an embodiment of the filter circuit that is an RLC circuit, Figure 27d shows an embodiment of the filter circuit that is a Butterworth filter, and Figure 27e shows an embodiment of the filter circuit that is an active filter circuit using operational amplifiers. [Figure 28] FIG. 2 shows the voltage gain of an operational amplifier plotted against frequency. [Figure 29] FIG. 13 illustrates the transient currents caused by the lowering and raising of the grabber device when depositing and removing a storage container. [Fig. 30a-30b] FIG. 2 shows the Fourier transform of the current through a rechargeable power source. [Figure 30c] FIG. 2 shows the Fourier transform of the current through a rechargeable power source. [Figure 30d] FIG. 2 shows the Fourier transform of the current through a rechargeable power source. [Diagram 31] A diagram showing a simulation model of a simple RC circuit. [Diagram 32] Figure 32a shows the load current as in Figure 29. Figure 32b shows the current through a 20Hz filter circuit. Figure 32c shows the current through a 7Hz filter circuit. [Diagram 33] Figure 33a shows a comparison between the load current and the current through a 20Hz filter circuit, and Figure 33b shows a comparison between the load current and the current through a 7Hz filter circuit. [Diagram 34] 1 is a diagram showing a discharge curve of a lithium-ion battery cell. [Diagram 35] FIG. 1 shows the shape of the discharge curves of a battery and a supercapacitor. [Diagram 36] FIG. 2 illustrates the power demands of a load handling device when moving on a storage grid. [Figure 37] FIG. 1 is a simplified circuit diagram of a supercapacitor 102 connected in series with a rechargeable power source 100. [Figure 38] Diagram showing a multi-cell battery connected in series with an assembly of supercapacitors in parallel with multiple electrical loads. [Figure 39] FIG. 1 is a circuit diagram showing a controller directing charge from a rechargeable power source to a supercapacitor. [Diagram 40] Schematic showing the controller directing harvested energy to a supercapacitor. [Diagram 41] FIG. 2 is a detailed diagram of one embodiment of a controller and a DC-DC converter. [Diagram 42] FIG. 2 shows a supercapacitor protection circuit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] A rechargeable power source configured to provide power to an assembly of one or more supercapacitors. 7 is a circuit diagram showing a rechargeable power source 100 connected in parallel to a supercapacitor 102 and an electrical load 104. The electrical load 104 may comprise one or more motors that drive a set of wheels 34 and 36 to enable the movement of the vehicle in the X and Y directions, respectively, along the rails, and / or one or more motors that drive a lifting device or crane mechanism to lift a storage container from above. The supercapacitor 102 is connected between the rechargeable power source 100 and the electrical load 104, such that the rechargeable power source can provide power to or receive power from the supercapacitor, and the supercapacitor can provide power to or receive power from the electrical load.

[0039] 7 illustrates the rechargeable power source 100 as a single battery cell and the supercapacitor 102 as a single supercapacitor. It will be appreciated that the rechargeable power source is not limited to a battery, and that a battery may comprise an assembly of one or more battery cells rather than a single battery cell.

[0040] Similarly, supercapacitor 102 may comprise an assembly of one or more supercapacitor modules rather than a single supercapacitor module.

[0041] [DCDC converter] The circuit may additionally comprise a source DCDC converter 108 between the rechargeable power source 100 and the supercapacitor 102. The purpose of the source DCDC converter 108 is to convert the voltage on the rechargeable power source to a different voltage on the supercapacitor.

[0042] The source DCDC converter 108 between the rechargeable power source 100 and the supercapacitor 102 can comprise a boost converter or a buck converter. Advantageously, the source DCDC converter 108 between the rechargeable power source 100 and the supercapacitor 102 can comprise a boost converter. The advantage of a higher voltage on the supercapacitor is that the supercapacitor can store more energy. Also, as a result of the higher voltage (and therefore lower current), the power loss due to resistance (P=I^2R) is smaller, thus reducing the amount of useful energy converted to heat.

[0043] The circuit may additionally include a load DCDC converter 110 between the supercapacitor 102 and the electrical load 104. The purpose of the load DCDC converter 110 between the supercapacitor 102 and the electrical load 104 is to convert the voltage on the supercapacitor to a different voltage on the electrical load.

[0044] The load DCDC converter 110 between the supercapacitor 102 and the electrical load 104 may include a step-up converter or a step-down converter.

[0045] 8 is a circuit diagram showing both a source DCDC converter 108 between a rechargeable power source 100 and a supercapacitor 102, and a load DCDC converter 110 between the supercapacitor 102 and an electrical load 104. Although FIG. 8 shows both DCDC converters, it will be understood that the present invention encompasses circuits that include a source DCDC converter 108 but not a load DCDC converter 110, and circuits that include a load DCDC converter 110 but not a source DCDC converter 108.

[0046] Advantageously, the source DCDC converter 108 between the rechargeable power source 100 and the supercapacitor 102 is a digitally controlled boost converter, and the load DCDC converter 110 between the supercapacitor 102 and the electrical load 104 is a buck converter.

[0047] 9 is a circuit diagram in which the source DCDC converter 108 between the rechargeable power source 100 and the supercapacitor 102 is a step-up converter, and the load DCDC converter 110 between the supercapacitor 102 and the electrical load 104 is a step-down converter. A controller 114 can be used to keep the supercapacitor voltage within a desired range with minimal current draw from the rechargeable power source.

[0048] The advantage of the source DCDC converter 108 between the rechargeable power source 100 and the supercapacitor 102 being a step-up converter is that the supercapacitor voltage will not drop below the voltage of the rechargeable power source. The load DCDC converter can therefore be powered by a simple step-down converter to power the electrical load 104. The energy recovered from the deceleration event can be directed to the supercapacitor by the energy recovery circuit 112. This circuit can be as simple as a power diode to control the flow of current from the electrical load to the supercapacitor.

[0049] [Controlling supercapacitor charging] An important issue to consider is how to control the state of charge of the supercapacitor: if the supercapacitor is fully charged, after a subsequent deceleration event the recovered energy cannot be stored in the supercapacitor, in which case the recovered energy needs to be either directed to a rechargeable power source (and thus contribute to battery aging if the rechargeable power source is a battery) or dissipated as heat.

[0050] 10 shows one possible embodiment of the controller 114 as a PID controller. One option is for the controller 114 to allow the rechargeable power source to charge the supercapacitor only when the charge on the supercapacitor falls below a predetermined supercapacitor target voltage threshold. This can be done by measuring the voltage Vc on the supercapacitor and allowing the rechargeable power source to charge the supercapacitor only when the voltage on the supercapacitor falls below a predetermined supercapacitor target voltage threshold. The predetermined supercapacitor target voltage threshold Vr is compared to the instantaneous supercapacitor voltage Vc and the controller 114 adjusts its output accordingly.

[0051] [Energy Recovery] During a deceleration event, kinetic energy can be recovered from the deceleration of the load handling equipment and stored in a supercapacitor for subsequent use.

[0052] The energy storage system of the load handling device must be capable of receiving power from the drive mechanism during a deceleration event in which the load handling device decelerates from its maximum speed in either the X or Y direction until it comes to rest at a different grid location. The drive mechanism may include one or more electric motors that act as generators during the deceleration event to convert the kinetic energy of the load handling device into electrical energy that can be stored in supercapacitors for subsequent use.

[0053] The energy storage system of the load handling equipment must be able to receive power from the lifting mechanism during a deceleration event when the grabber device is lowered to a lower vertical position within the storage grid. As the grabber is lowered, potential energy from its higher vertical starting position is converted into kinetic energy. The lifting drive assembly may include one or more electric motors that act as generators during the deceleration event to convert the kinetic energy of the lowering platform into electrical energy that can be stored in supercapacitors for subsequent use.

[0054] It will be appreciated that during the lowering operation when the grabber device is gripping the storage container, the mass of the storage container means that the higher the vertical starting position of the grabber device and storage container, the more potential energy there is to be recovered therefrom, so more energy can be recovered.

[0055] The recovered energy can be transferred into the supercapacitor 102 by an energy recovery circuit 112, as shown in Figure 11. The purpose of the energy recovery circuit 112 is to direct current into the supercapacitor 102. This is advantageous because if the recovered energy is directed into a rechargeable power source, the number of charge-discharge cycles will increase, accelerating the aging of the battery if the rechargeable power source is a battery. The energy recovery circuit can comprise one or more diodes or transistors.

[0056] The assembly of one or more supercapacitor modules can have a lower internal resistance than the rechargeable power source to ensure that recovered energy is directed to the supercapacitor and not the rechargeable power source.

[0057] [Sizing the supercapacitor to receive and store the recovered energy] The predetermined supercapacitor target voltage threshold may be selected to be lower than the supercapacitor maximum rated voltage and such that the difference between the predetermined supercapacitor target voltage threshold and the maximum rated voltage of the supercapacitor is sufficient for the supercapacitor to receive energy recovered from one or more deceleration events, and the power rating of the supercapacitor may be selected to be sufficient to receive power from the deceleration events.

[0058] An assembly of supercapacitor modules can be sized such that the difference between a predetermined supercapacitor target voltage threshold and the maximum rated voltage of the supercapacitor is sufficient to receive and store energy from one deceleration event.

[0059] Alternatively, an assembly of supercapacitor modules may be sized such that the difference between a predetermined supercapacitor target voltage threshold and the maximum rated voltage of the supercapacitor is sufficient to receive and store energy from multiple deceleration events. For example, if a load handling device is required to move to a different grid cell in the Y direction and place a storage container, this operation comprises four acceleration / deceleration events: accelerating in the Y direction to a maximum speed (acceleration event), decelerating in the Y direction to rest above the target grid cell (deceleration event), lowering the grabber device and the storage container from the container receiving space of the load handling device to a lower vertical position to place the storage container (deceleration event), and raising the grabber device back to the load handling device (acceleration event). In this sequence of events, there are two consecutive deceleration events. Sizing an assembly of one or more supercapacitor modules such that the difference between a predetermined supercapacitor target voltage threshold and the maximum rated voltage of the supercapacitor is sufficient to receive and store energy from both deceleration events means that a supercapacitor alone can be used for this operation, thus reducing the number of power cycles required for the rechargeable power source and potentially extending its life. In general, it is an advantage that the energy capacity of the supercapacitor is sufficient for two or more normal deceleration events, so that under normal operation the rechargeable power source does not need to receive energy from acceleration events. Reversing the direction of the current through the rechargeable power source accelerates the ageing process and reduces its lifetime if the rechargeable power source is a battery.

[0060] Sizing the supercapacitor such that the difference between the predetermined supercapacitor target voltage threshold and the maximum rated voltage of the supercapacitor is sufficient to receive and store energy from multiple deceleration events is advantageous because it ensures that energy flows only one way to and from the rechargeable power source, even in the event of unexpected fast deceleration events during normal operation on the grid. The supercapacitor effectively performs charge-discharge cycles from acceleration / deceleration events, protecting the rechargeable power source from the aging effects of these cycles. Rather than undergoing charge-discharge cycles for every acceleration / deceleration event, as would be the case if the rechargeable power source were the only power source in the energy storage system, the rechargeable power source instead only needs to provide a constant "top-up" of energy to the supercapacitor at low power. This has the added benefit of making it easier to provide a smooth, constant current profile to the rechargeable power source.

[0061] If the source DC-DC converter 108 between the rechargeable power source and the supercapacitor is a boost converter, the predetermined supercapacitor target voltage threshold can be higher than the voltage of the rechargeable power source, which has the advantage that the supercapacitor 102 can store more energy since its energy storage capacity is proportional to the square root voltage.

[0062] One option is to set the minimum voltage of the supercapacitor to be equal to or greater than the voltage of the rechargeable power source. This has the advantage that the load DC-DC converter 110 can be a simple step-down converter to power the electrical load 104. Also, if the voltage of the supercapacitor is equal to or greater than the voltage on the electrical load, the energy recovery circuit 112 can be kept as simple as a power diode. The disadvantage of this option is that only a part of the voltage range of the supercapacitor can be used.

[0063] Allowing the supercapacitor voltage to drop below the voltage of the rechargeable power source allows a greater range of supercapacitors to be used, but means that more complex electronics are required rather than a simple boost converter between the rechargeable power source and the supercapacitor. Also, if the supercapacitor voltage drops below the voltage on the electrical load, the energy recovery circuit 112 needs to become more complex to avoid over-voltage of the supercapacitor. Voltages that exceed the maximum rating of the supercapacitor reduce the operating life of the cell and eventually lead to failure.

[0064] For example, if the voltage of the rechargeable power source and the electrical load are both nominally 48V, the predetermined supercapacitor target voltage threshold may be set to 60V. The supercapacitor may be selected to have a maximum rated voltage of 72V, so that the supercapacitor has sufficient energy storage capacity to store the energy recovered from the deceleration event. If the supercapacitor voltage falls below 60V, the controller causes the rechargeable power source to charge the supercapacitor. If the supercapacitor voltage exceeds 60V, the controller 114 does not cause the rechargeable power source to charge the supercapacitor. The supercapacitor continues to provide energy for the acceleration event until the voltage falls below 60V, after which the controller allows the rechargeable power source to charge the supercapacitor again. To simplify the required electronics in the source DC-DC converter 108 and the energy recovery circuit 112, the supercapacitor 102 may be limited to operating above a minimum operating voltage of 48V.

[0065] [Non-powered power load] The electrical loads can comprise both power and non-powered power loads. Powered power loads are due to the demands of the drive mechanism and / or lift drive assembly and change with the movement of the load handling apparatus. Non-powered power loads are power loads for all functions other than the operation of the load handling apparatus and can include, for example, power for communication with a storage grid control system. These non-powered power loads are always present regardless of the movement of the load handling apparatus. FIG. 12 shows a circuit diagram with a non-powered power load 106. The non-powered power loads can be powered by a rechargeable power source 100.

[0066] [Sizing supercapacitors for acceleration events] The energy storage system of the load handling equipment must be capable of providing power to the drive mechanism to enable movement of the load handling equipment on the grid in the X and Y directions. Movement in the X or Y direction comprises an acceleration event where the load handling equipment starts from rest and reaches a maximum speed, followed by a deceleration event where the load handling equipment moves from the maximum speed to rest at a different grid location. Typically, each acceleration event is followed by a deceleration event.

[0067] The energy storage system of the load handling apparatus must be capable of providing power to enable the lifting drive assembly to lower and raise the grabber device to retrieve or place the storage container. A lifting operation comprises a deceleration event in which the grabber device is lowered from the load handling apparatus to a lower vertical position within the grid framework, followed by an acceleration event in which the grabber device grabs the storage container and raises it vertically upward into a container receiving space within the load handling apparatus. Similarly, a placing operation comprises a deceleration event in which the grabber device holding the storage container is lowered from the load handling apparatus to a lower vertical position within the grid framework where the storage container is placed, followed by an acceleration event in which the grabber is raised vertically upward to the load handling apparatus. Typically, each deceleration event is followed by an acceleration event.

[0068] An assembly of supercapacitor modules can be sized so that the power rating is sufficient to provide power for one acceleration event.

[0069] Alternatively, an assembly of supercapacitor modules may be sized such that the power rating is sufficient to power multiple acceleration events. For example, if a load handling device is required to pick up a storage container and move it to a different grid cell in the X direction, this operation comprises four acceleration / deceleration events: lowering the grabber device (deceleration event), raising the grabber device and the storage container to place the storage container in the container receiving space (acceleration event), accelerating to a maximum speed in the X direction (acceleration event), and decelerating to rest above the target grid cell (deceleration event). In this sequence of events, there are two consecutive acceleration events. Sizing an assembly of one or more supercapacitor modules such that the power rating is sufficient to power both acceleration events means that a supercapacitor can be used alone for this operation, thus reducing the number of power cycles of the rechargeable power source required and potentially extending the life of the rechargeable power source. In general, the advantage is that the supercapacitor power is sufficient for two or more normal acceleration events, so that under normal operation, the rechargeable power source does not need to provide power for the acceleration events, but only needs to top up the supercapacitor when its charge drops below a given level. Even if there is an unexpected high speed acceleration, the rechargeable power source is still protected from power cycling.

[0070] The supercapacitors can be sized to have enough power and energy available to complete the most energy-demanding acceleration event, which may be an X or Y directional movement across the entire length of the storage grid.

[0071] [Circuit operation] 13-18 show the operation of the circuit during different states of the load handling apparatus, i.e., during a deceleration event, during an idling period, and during an acceleration event. In each case, the operation of the circuit is shown while the rechargeable power source is charging the supercapacitor and while the rechargeable power source is not charging the supercapacitor. The arrows on the diagrams indicate the direction of current flow.

[0072] 13 illustrates operation of the circuit while the load handling equipment is undergoing a deceleration event. Energy is recovered from the electrical load 104 (e.g., from the drive or lifting mechanism) and directed to the supercapacitor 102 by the energy recovery circuit 112. The rechargeable power source 100 provides power to the non-motor power load 106. Effectively, the circuit diagram is two separate circuits.

[0073] 14 illustrates operation of the circuit while the load handling equipment is undergoing a deceleration event and the rechargeable power source is charging the supercapacitor. Energy is recovered from the electrical load 104 (e.g., from the drive or lifting mechanism) and directed to the supercapacitor 102 by the energy recovery circuit 112. The rechargeable power source 100 provides power to the supercapacitor 102 and the non-motor power load 106. For this to occur, the supercapacitor power rating must be sufficient to receive power from both the energy recovery circuit and the rechargeable power source.

[0074] 15 illustrates operation of the circuit while the load handling equipment is idling. The rechargeable power source 100 provides power to the non-motor power load 106. The source DC-DC converter 108 can be disconnected so that no power is provided to the supercapacitor 102.

[0075] 16 illustrates the operation of the circuit while the load handling equipment is idling and the rechargeable power source is charging the supercapacitor. The rechargeable power source 100 provides power to the non-motor power load 106 and the supercapacitor 102. The load DCDC converter 110 can be disconnected so that no power is provided to the electrical load 104. The circuit can have an active mode in which acceleration of the load handling equipment is expected soon, in which case the load DCDC converter 110 can be connected in preparation for providing power to the electrical load 104.

[0076] 17 illustrates operation of the circuit while the load handling equipment is undergoing an acceleration event. Power is provided to an electrical load 104 (e.g., a drive mechanism or lifting mechanism) by a supercapacitor 102. A rechargeable power source 100 provides power to a non-motor power load 106. Effectively, the circuit diagram is two separate circuits.

[0077] 18 illustrates operation of the circuit while the load handling equipment is undergoing an acceleration event and the rechargeable power source is charging the supercapacitor. Power is provided by the supercapacitor 102 to an electrical load 104 (e.g., a drive mechanism or a lifting mechanism). The rechargeable power source 100 provides power to a non-motor power load 106. If the impedance of the electrical load 104 is lower than the impedance of the supercapacitor 102, the rechargeable power source 100 can provide power to the supercapacitor 102; otherwise, the rechargeable power source 100 can provide power to the electrical load.

[0078] [Rechargeable power source provides average current] One of the main advantages of using supercapacitors to provide power to load handling equipment is that supercapacitors experience charge / discharge cycles instead of rechargeable power sources, which are exposed to average currents rather than cycles.

[0079] FIG. 19 is an illustration of the principle of using supercapacitors. The current through the electrical load is plotted against time as a storage container weighing 15 kg is lowered to a depth of 12 grid cells in a grid storage system and then raised again. The solid line represents the current provided to / recovered from the lifting drive assembly (electrical load). The graph first shows a deceleration event, in which the lifting drive assembly lowers the storage container from the container receiving space of the load handling device into the storage grid, and kinetic energy is recovered from the storage container and converted to electrical energy by the lifting drive assembly (negative current). Then an acceleration event is shown, in which energy is provided to the lifting drive assembly to lift the storage container to the top of the storage grid and place the storage container in the container receiving space of the load handling device (positive current). If only a rechargeable power source is used to power the lifting drive assembly of the load handling device, the rechargeable power source is exposed to transient currents of up to 23 amps (deceleration) and 14 amps (acceleration). These surges in current, along with the transient nature of the current, result in multiple partial charge / discharge cycles that accelerate the aging of the rechargeable power source, especially when the rechargeable power source is a battery.

[0080] The dotted line in FIG. 19 represents the average current required by the electrical load. The average current is approximately 1 ampere (deceleration). If a supercapacitor placed between the rechargeable power source and the electrical load acted as a perfect filter, the entire current signal, including all of the transients, would be picked up by the supercapacitor and the rechargeable power source would be exposed to an average current of 1 ampere. The elimination of transients means that the rechargeable power source would not be exposed to any charge-discharge cycles, greatly extending its expected lifespan. Supercapacitors are well suited to handle transients in the current because they have a high power density and do not suffer from premature aging from a large number of charge-discharge cycles.

[0081] The use of an assembly of one or more supercapacitor modules also improves the efficiency of the energy storage system. Power loss is proportional to the square root current, so when the current of the rechargeable power source is lowered, the power loss is significantly reduced. In the scenario described above and shown in FIG. 19, the heat generated inside the rechargeable power source during the lowering and lifting of a storage container weighing 15 kg to a depth of 12 grid cells is 230 J / Ω. By using an assembly of one or more supercapacitor modules to power the lowering and lifting of the storage container, the heat thus generated in the rechargeable power source is reduced to 2.8 J / Ω (calculated using the average current). This is an 82-fold reduction in the heat generated.

[0082] Improving efficiency and reducing power losses is especially important when the load handling equipment handles chilled or frozen goods in a fulfillment center that must be kept at a low temperature. The heat wasted from rechargeable power sources in the load handling equipment means that the fulfillment center's cooling systems must consume more energy to maintain the required low temperatures.

[0083] [Supercapacitor as primary power source, with auxiliary power provided by a rechargeable power source] In one embodiment of the invention, the supercapacitor 102 may be used as the primary power supply for the load handling equipment, with auxiliary power being provided by the rechargeable power source 100. This allows the load handling equipment to operate using the supercapacitor as the primary power source, thus benefiting from the advantages of fast charging of the supercapacitor at a supercapacitor charging station.

[0084] When the rechargeable power source is a battery, the relatively long charging time of the battery can be several hours long, which represents a significant amount of downtime during which the load handling equipment remains inactive or inoperable on the grid framework structure. If several load handling equipment are operable on the grid framework to fulfill customer orders within a given time slot, leaving one or more load handling equipment idle for a significant amount of time can have a devastating effect on the ability of a fulfillment center or distribution warehouse to fulfill orders in a timely manner. This is especially so when the load handling equipment contributes to a logistics system that provides home delivery of goods to customer premises upon receipt of the goods. Here, delivery information including a delivery address is used by online merchants such as Amazon and UK Ocado to deliver goods to the customer's delivery address. To mitigate such issues, online merchants such as UK Ocado provide a buffer of load handling equipment operable on the grid framework to accommodate load handling equipment that remains idle for charging. In extreme cases, the time slot for delivery of the order is extended to accommodate this downtime. The use of supercapacitors as the primary power source eliminates the drawbacks of slow battery charging, reducing downtime and contributing to the efficient fulfillment of customer orders.

[0085] Batteries, primarily based on lithium-ion, nickel-cadmium, nickel-metal hydride, or lithium-ion polymer battery technology, utilize chemical reactions to store electrical energy. The effectiveness of these batteries diminishes due to the breakdown of lithium-ion cells after repeated charging, and therefore the ability of the battery to store a charge for extended periods of time diminishes over time.

[0086] Charging stations for supercapacitors typically operate at higher currents than charging stations for batteries because supercapacitors have a higher power density and can therefore accept charges at higher powers (which also have the advantage of faster charging). Two types of charging stations may be provided in the storage grid, one with a higher power rating / higher current for charging supercapacitors and one with a lower power rating / lower current for charging rechargeable sources.

[0087] The load handling apparatus may be controlled by a control system that monitors the charge level of the energy storage system. The control system determines whether the energy storage system of the load handling apparatus needs charging and directs the load handling apparatus to travel to a charging station if the charge level falls below a predetermined threshold charge level. In a dual power source, the control system can determine whether the supercapacitor or the rechargeable power source needs to be charged, choose the appropriate charging station, and direct the load handling apparatus to travel to the selected charging station on the storage grid.

[0088] Alternatively, a single type of combined charging station can be provided, which may be configured to provide low current (for slow charging of the rechargeable power source) or high current (for fast charging of the supercapacitor). The control system determines when the energy storage system of the load handling device needs charging, determines whether the supercapacitor or the rechargeable power source needs to be charged, selects the appropriately combined charging station, directs the load handling device to travel to the selected charging station on the storage grid, and determines whether the high or low charging current should be used.

[0089] The charging station can be an inductive wireless charging station.

[0090] In this embodiment of the invention, the assembly of one or more supercapacitors is the primary power source, so that most of the charging is fast charging the assembly of one or more supercapacitor modules, and charging of the rechargeable power source is required only infrequently when the rechargeable power source becomes depleted.

[0091] [Supplemental power from rechargeable sources after grid downtime] Occasionally, the entire storage system needs to be offline for a short period of time (known as grid downtime) to perform maintenance work or to resolve issues with the load handling equipment. This creates problems if the load handling equipment is powered only by supercapacitors as the main power source. Supercapacitors have a high self-discharge rate and typically after an hour of outage the supercapacitors may be partially discharged below a certain threshold voltage for powering the electrical loads, in which case they are unable to provide the power required to enable the load handling equipment to move on the storage grid. After the grid downtime ends and the load handling equipment is restarted, the load handling equipment may not be able to return to the charging station under its own power. The load handling equipment needs to be removed from their position on the grid and sent to the charging station before they can be operational again, which extends the grid downtime period.

[0092] This problem is solved by using the rechargeable power source as a backup power when the primary power source, the supercapacitor, is discharged, especially when the rechargeable power source is a battery. Batteries have the advantage of a low self-discharge rate, so they are not heavily discharged after a period of outage. After grid downtime for maintenance work, when the state of charge of the supercapacitor drops to a level where it cannot provide the required power, the rechargeable power source can provide backup power to the electrical loads to enable movement of the load handling equipment.

[0093] The load handling equipment can switch to running on power from the rechargeable power source 100 when the supercapacitors 102 are partially or fully discharged, thus eliminating the risk of the load handling equipment running out of power and becoming stranded on the grid, requiring downtime to retrieve the load handling equipment and send it to a charging station.

[0094] [Supercapacitor in low temperature environment] Supercapacitors improve battery technology in low temperature environments, thereby making load handling equipment that is primarily powered by supercapacitors particularly well suited for these operating conditions.

[0095] The load handling equipment may operate in a fulfillment center where temperatures are kept low, for example when fulfilling customer orders for chilled or frozen goods. All wasted heat from the load handling equipment's energy storage system not only represents a waste of energy, but also requires more energy consumption to keep the fulfillment center temperature low.

[0096] Table 2 shows the performance of a bank of Li-ion batteries powering a load handling device on a grid frame structure.

[0097] [Table 2]

[0098] Typically, Li-ion batteries require 15 minutes of charging for every 4 hours of discharge. During operation on the grid framework structure over a 4 hour period, the power on the electrical load reaches a peak of 600W, and at idle, 96W due to the power consumed by the communication between the control unit in the load handling equipment and the central control system via the communication device. The average power consumed by the electrical load is considered to be 400W over a 4 hour period, corresponding to an energy consumption of 100Wh per operating cycle. The energy storage system on the load handling equipment must store at least 100Wh of energy when fully charged. The Li-ion battery has a service life of 3 years at ambient controlled temperatures (10°C to 30°C) and 0.5 years at chilled temperatures (0.5°C).

[0099] In contrast to Li-ion batteries, supercapacitors do not suffer from the problem of reduced lifetime when operated at low temperatures: they are typically rated to operate at temperatures as low as -40°C and do not suffer from any degradation in performance.

[0100] The load handling equipment may be required to operate in a low temperature environment if the storage system is for chilled or frozen goods. In particular, the storage system may be located in a fulfillment center having a chilled or frozen temperature environment, and the load handling equipment needs to be able to operate in this environment. Frozen temperatures cover a range between substantially -25°C and substantially 0°C, and chilled temperatures cover a range between substantially 0°C and substantially 4°C. Thus, the supercapacitors are typically within their rated operating temperatures in a chilled or frozen temperature environment.

[0101] As an example, Table 3 shows the calculated charging currents for different desired charge and discharge times at 48 volts applied to a commercial supercapacitor module charged with an initial energy of 100 Wh. The average power consumption over a 4 hour period as shown in Table 2 for a Li-ion battery is considered to be 400 W. The charging times shown in the table for the supercapacitor (5 to 30 seconds) are significantly faster than the Li-ion battery (typically 15 minutes).

[0102] Table 4 shows the equivalent energy used for different discharge times and the equivalent depth of discharge of the supercapacitor, assuming an initial charge of 100Wh. The average power consumed by a Li-ion battery in a load handling device as shown in Table 2 is 400W. To receive the same power from a supercapacitor initially charged to provide 100Wh, the supercapacitor would need to be fully discharged at 100% depth of discharge every 15 minutes. Similarly, a 5 minute discharge time represents a depth of discharge of 33% and an equivalent energy of 33Wh.

[0103] Depending on the operation of the load handling apparatus on the grid framework structure, and thus the power consumed by the load handling apparatus when performing operations on the grid framework structure, short bursts of energy can be delivered to the supercapacitor modules by visiting one or more supercapacitor charging stations to top up the supercapacitor modules sufficiently to enable the load handling apparatus to complete operations. Compared to the time it takes to perform operations on the grid framework structure, the charging time of a bank of supercapacitor modules is a small fraction of that time. Because the charging time is relatively short (on the order of a few seconds) and because the supercapacitors can withstand multiple charging cycles, the load handling apparatus can visit multiple charging stations during operation on the grid framework structure. For example, the supercapacitors can be cycled to 100% depth of discharge 290,000 times, which equates to a useful life of about 8 years, which is significantly longer than the useful life of a typical battery.

[0104] [Table 3]

[0105] [Table 4]

[0106] [Distributing supercapacitor modules to lower the center of mass of a load handling device] In one embodiment of the invention, the load handling apparatus occupies only one grid space or grid cell of the grid framework structure (as shown in Figures 4 and 5). This has the advantage that a greater number of load handling apparatuses can be active on the grid at any given time. However, the load handling apparatus shown in Figure 5 having a container receiving recess 40 at its bottom has the lifting drive assembly, drive mechanism and energy storage system located above the container receiving recess. A disadvantage of this arrangement is that the center of mass of the load handling apparatus is high, which adversely affects the stability of the load handling apparatus.

[0107] To lower the center of mass and therefore improve the stability of the load handling apparatus, one or more supercapacitor modules may be distributed around the outside between the container receiving recesses. Figure 20 shows a load handling apparatus 30 with a container receiving recess 40 located within a body 32. The body 32 includes four exterior walls 42 on four sides of the load handling apparatus 30 and four interior walls 44 that form the interior surface of the body within which the container receiving recesses 40 are located. Between the interior walls 44 and the exterior walls 42 of the body there is an air gap 46.

[0108] 21 illustrates how a supercapacitor module 48 may be positioned within the gap 46 between the inner wall 44 and the outer wall 42. It will be appreciated that because the supercapacitor module 48 is positioned lower within the load handling apparatus, the center of mass of the load handling apparatus is lowered. In an alternative arrangement, an assembly of one or more supercapacitor modules would be positioned in the upper portion of the load handling apparatus above the container receiving recess 40. As a result of the lowered center of mass, the load handling apparatus is more stable.

[0109] The stability of the load handling equipment is an important consideration. An unstable load handling equipment may be at risk of tipping over, thereby requiring grid down time to remove the load handling equipment and return it to an upright position.

[0110] [Recalibrate battery state of charge calculations based on periods of low current drain] FIG. 22 shows the charge-discharge profile of a lithium-ion battery in a load handling device, plotting the state of charge (SOC) of the battery against the battery voltage. The data was measured after one day of operation of the load handling device on the grid. Three sets of data are plotted: i) the SOC obtained from measuring the battery voltage at a range of different battery current values, ii) the open circuit voltage curve from the battery manufacturer's data sheet, and iii) the SOC estimate from the battery fuel gauge at a range of different battery current values. Since i) and iii) were measured at a range of different current values, there are several sets of data rather than a single line. The data points for ii) are at a single current (open circuit voltage corresponds to zero current), so there is a single data line. It can be seen from FIG. 22 that the subset of data points for both i) the SOC obtained from measuring the voltage and iii) the SOC estimate from the battery fuel gauge that are aligned and aligned with the manufacturer data are measurements at zero current. This alignment indicates that the battery fuel gauge is accurately measuring the true SOC of the battery.

[0111] Battery fuel gauge SOC estimation is based on a coulomb counting method, which measures the current drawn from and supplied to the battery and integrates it over time to estimate the remaining available charge. Coulomb counting is advantageous in that it is a simple method to implement and easy to understand, but because current measurements cannot be perfectly accurate, the method can be subject to drift over time if the measurements are not recalibrated to a reference point.

[0112] FIG. 23 shows the charge-discharge profile of a lithium-ion battery in a load handling device, plotting SOC against battery voltage in the same manner as in FIG. 22. The data was measured after several days of continuous operation of the load handling device on the grid. Again, three data sets are plotted: i) the SOC obtained from measuring the battery voltage at a range of different battery current values, ii) the open circuit voltage curve from the battery manufacturer's data sheet, and iii) the SOC estimate from the battery fuel gauge at a range of different battery current values. It can be seen from FIG. 23 that the SOC obtained from measuring the voltage still aligns with the manufacturer data along the charge profile curve. However, this is not the case for the SOC estimate from the battery fuel gauge, which does not align with the manufacturer data. There is a gap between the battery fuel gauge reading of SOC and the actual SOC, represented by the arrow in FIG. 23. This gap can be as large as 15-25% SOC, indicating that the battery fuel gauge is no longer accurately reporting the true SOC of the battery, and in fact significantly over-estimates the available SOC. This is the case for both the charge and discharge curves.

[0113] This inaccuracy in the SOC estimate by the battery fuel gauge is problematic because the SOC is used by the control system to determine when the batteries should be recharged. For example, the control system may require the load handling equipment to proceed to a charging station when the SOC drops below 30%. When the battery fuel gauge indicates the SOC has dropped to 30%, the true SOC may be 10-15% lower. This is problematic because it increases the risk that the load handling equipment's batteries will run out of charge before it can reach the charging station. In this situation, it may be necessary to shut down the grid while the load handling equipment is removed and taken to the charging station.

[0114] This inaccuracy in the battery fuel gauge's SOC estimate gradually increases with operating time: after one day of operation on the grid, the battery fuel gauge accurately reports the SOC (see FIG. 22), but after several days of continuous operation on the grid, the battery fuel gauge does not accurately report the SOC.

[0115] The problem here is that inaccuracies in tracking transient peaks in the current tend to cause the battery current to be underestimated. If the current transients occur more frequently than the battery fuel gauge measures the current, the peaks will not be captured accurately. Underestimating the current delivered by the battery can lead to an overestimation of the available charge remaining in the battery, which explains why the SOC estimate from the battery fuel gauge drifts upward over time. Underestimating the current delivered by the battery, even by a small amount, will get worse over time, resulting in a drift between the battery fuel gauge SOC estimate and the actual SOC.

[0116] This problem can be solved by recalibrating the battery fuel gauge by allowing the battery cells to experience a period of zero current, or low current drain where as little current as possible is drawn from the battery. This quiet period gives the battery fuel gauge an opportunity to recalibrate the SOC estimate, which tends to reduce "drift."

[0117] Recalibration can be done by checking whether the SOC estimate from the battery fuel gauge at a known voltage and current matches the expected SOC from the manufacturer data sheet at the same voltage and current. This can be any known current, but zero current is convenient because the open circuit voltage curve is readily available from the battery manufacturer. When the battery current is zero, the expected SOC for a given voltage can be read from the manufacturer's OCV curve. Thus, the battery fuel gauge can be recalibrated by identifying when the expected SOC differs from the battery fuel gauge SOC estimate and updating the battery fuel gauge SOC estimate to match the expected SOC.

[0118] An alternative method of estimating SOC is voltage measurement rather than coulomb counting. However, because battery voltage drops rapidly over time as the battery discharges, small changes in voltage correspond to large changes in SOC. This means that voltage-based SOC estimation is not always accurate. Coulomb counting can be a better way of estimating SOC than measuring voltage, assuming calibration issues can be addressed.

[0119] A load handling device having an energy storage system including an assembly of one or more supercapacitor modules and a battery can take advantage of dual power sources by using only the supercapacitors for short periods of time, allowing the battery to have periods of low current drain with zero or low current demand during which the battery fuel gauge can recalibrate its SOC reading and therefore indicate a more accurate SOC reading.

[0120] While zero current draw is ideal during periods of low current drain in order to recalibrate the battery fuel gauge to the manufacturer's open circuit voltage curve, in practice zero current draw may not be achievable, so current draw must be kept as low as possible. Periods of low current drain may be achieved by the controller periodically disconnecting the battery from the assembly of one or more supercapacitor modules such that no charge is delivered to the supercapacitors. "Periodic disconnect" means disconnecting for a short period of time once every predetermined period of time (e.g., once every four hours).

[0121] [Battery SOC Balancing] Individual cells within a battery pack will naturally have somewhat different capacities and therefore may be at different states of charge over a series of charge and discharge cycles. Capacity variations can be due to manufacturing variations, assembly variations (e.g., combining cells from one manufacturing run with others), cell aging, impurities, or environmental exposure (e.g., some cells may be exposed to additional heat from nearby sources such as motors, electronic devices, etc.), and can be exacerbated by the cumulative effects of parasitic loads, such as cell monitoring circuits often found within battery management systems.

[0122] A battery can have multiple battery cells connected in series. In this case, it is necessary to "balance" the battery by keeping the voltage / SOC in each cell as similar as possible. Balancing an assembly of battery cells helps to maximize the energy capacity and improve the service life of the battery.

[0123] A battery management system is used to monitor the condition of the battery pack, including individual cell characteristics such as temperature and voltage. When charging, the entire battery pack can only be charged until one cell reaches its maximum safe charging voltage, even if other battery cells still have the capacity to be further charged. Thus, the battery cell with the lowest voltage limits the charging voltage of the entire battery pack. Similarly, the battery pack can only be safely discharged until one cell is fully discharged, even if other battery cells may still have usable charge. Thus, the battery cell with the lowest charging capacity limits the charging capacity of the entire battery pack. If charging / discharging cannot be stopped when one cell reaches its limit, the battery cell may be permanently damaged. Lithium-ion batteries are particularly susceptible to chemical damage by too high a voltage or current.

[0124] Battery balancing redistributes energy from battery cells with higher energy capacity to battery cells with lower energy capacity. Battery balancing can be passive, where energy is drawn from the most charged cells and dissipated as heat, or active, where energy is drawn from the most charged cells and transferred to the least charged cells. Active battery balancing can be performed by a DC-DC converter.

[0125] A load handling device having an energy storage system including an assembly of one or more supercapacitor modules and a battery can utilize a dual power source by using the supercapacitor to meet the acceleration demands of the load handling device while drawing a constant low current from the battery below a predetermined threshold current. The constant low current draw below a predetermined threshold current provides optimal conditions for battery cell balancing. The optimal predetermined threshold current depends on the size and specifications of the battery and can be determined by the battery manufacturer. For example, the predetermined threshold current may be a current below 3 amps.

[0126] [Opportunistic charging of supercapacitors at grid locations above access points] To fulfill a customer order, the load handling equipment can pick up a storage container and transport it to a grid location above an access point on the storage grid. The storage container is then lowered down a chute to the access point where it can then be accessed to fulfill the order. An operative can take an item from the storage container at the access point and pack it as part of the customer order. The load handling equipment can then raise and retract the storage container upwards, through the grid into a container receiving space, and then replace the storage container in the appropriate position within the storage grid.

[0127] Grid locations above access points on a storage grid are ideal locations for charging one or more assemblies of supercapacitor modules because load handling equipment must frequently travel to these locations to bring storage containers to the access points. The storage system may therefore include one or more supercapacitor charging stations located at grid locations above the access points.

[0128] Advantageously, the supercapacitor charging station can be a high-rate inductive supercapacitor charging station, whereby charging of the supercapacitors during lifting and lowering operations can be done by high-rate inductive charging. This allows the supercapacitors to be fully charged in a short time (on the order of a few seconds). Since charging of the supercapacitors is very fast, charging can be completed within the time that the load handling equipment spends at the grid location while lowering and lifting the storage container. Since the load handling equipment frequently visits the grid location above the access point, these visits can be sufficient for all the capacitor charging requirements. The load handling equipment does not need to make separate visits to other charging stations to charge one or more assemblies of supercapacitor modules. Thus, charging of the supercapacitors can be done during normal operation of the load handling equipment, and no extra time is required.

[0129] After the supercapacitors are charged at a grid location above an access point on the storage grid during a lifting or lowering operation, the supercapacitors may then be used to charge a rechargeable power source. This may be accomplished by a controller on the load handling apparatus commanding an assembly of one or more supercapacitor modules to charge the rechargeable power source. Alternatively, when the load handling apparatus is going to a grid location for a lifting or lowering operation, the supercapacitors can be used to charge the rechargeable power source in advance, so that the supercapacitors are partially discharged and ready to be charged by the supercapacitor charging station.

[0130] The supercapacitor may be used to charge the rechargeable power source at a low current. As explained above, if the rechargeable power source is a battery, exposing the battery to a constant low current below a predetermined threshold current is useful for balancing the battery cells to ensure a uniform state of charge across the different cells, thereby extending the life of the battery. The current may be limited to allow for balancing of the battery. The controller may command the supercapacitor to charge the rechargeable power source at a current below the predetermined threshold current.

[0131] If the supercapacitors are charged frequently enough and at a high enough charge rate, it may become possible for the rechargeable power source to be charged solely from the supercapacitors. This removes the requirement for a separate charging station on the storage grid to charge the rechargeable power source. This removes the requirement for the load handling equipment to travel to a rechargeable power source charging station on the storage grid and spend time there while the rechargeable power source is being charged. The need for downtime to charge the load handling equipment is effectively eliminated, allowing the load handling equipment to operate continuously on the storage grid.

[0132] As explained above, the load handling apparatus may be controlled by a control system monitoring the charge level of the rechargeable power source and commanding the load handling apparatus to go to a charging station if the charge level falls below a predetermined threshold charge level. In this embodiment of the invention, where the load handling apparatus can operate continuously on a storage grid without having to visit a charging station for the rechargeable power source, the supercapacitor charging station enables the load handling apparatus to maintain the voltage level of the rechargeable power source above a predetermined threshold voltage for powering the electrical load.

[0133] Recalibration of the battery state of charge estimate as described above is particularly important in situations where the load handling equipment is continuously operating on a storage grid.

[0134] [Battery / Supercapacitor Technology] It will be appreciated that an assembly of one or more supercapacitor modules may comprise, but is not limited to, a capacitor, a supercapacitor, an ultracapacitor, a lithium capacitor, an electrochemical double layer capacitor, an electric double layer capacitor, a pseudocapacitor, a hybrid capacitor, or some combination of these capacitor technologies.

[0135] It will be appreciated that the rechargeable power source may comprise, but is not limited to, a lithium ion battery, a lithium ion polymer battery, a lithium air battery, a lithium iron battery, a lithium iron phosphate battery, a lead acid battery, a nickel cadmium battery, a nickel metal hydride battery, a nickel zinc battery, a sodium ion battery, a sodium air battery, a thin film battery, a solid state battery, or a smart battery carbon foam based lead acid battery, or some combination of these technologies.

[0136] [Advantages of using a low-pass filter] The low pass filter circuit is advantageous for reducing the number of transient current cycles in the rechargeable power source. High frequency transients in the current provided to the electrical load are "smoothed" by the low pass filter circuit, so that the high frequency transient components of the current passing through the rechargeable power source are removed. This protects the rechargeable power source from surges in current draw. This is particularly advantageous when the rechargeable power source is a battery, since reducing the transients in the current has been shown to reduce the aging effects of the battery.

[0137] The elimination of transients means that the rechargeable power source is not subjected to any charge-discharge cycles, greatly extending its expected useful life. Supercapacitors are well suited to handle transients in electrical current because they have a high power density and do not suffer from premature aging from a large number of charge-discharge cycles.

[0138] The use of a low pass filter also improves the efficiency of the rechargeable power supply: since power loss is proportional to the square root of the current, lower current results in significantly reduced power loss.

[0139] Improving efficiency and reducing power losses is especially important when the load handling equipment handles chilled or frozen goods and the fulfillment center needs to be kept cool. Wasted heat from rechargeable power sources in the load handling equipment means that the fulfillment center's cooling system needs to consume more energy to maintain the required cool temperatures.

[0140] [Circuit diagram featuring a low-pass filter] 24 is a circuit diagram showing that the rechargeable power source 100 is connected in parallel to an electric load 104 and a filter circuit 116. The electric load 104 may comprise one or more electric motors that enable the vehicle to move along the rails in the X and Y directions, respectively, by driving the sets of wheels 34 and 36, and / or one or more motors that drive a lifting device or crane mechanism to lift the storage container from above.

[0141] For ease of explanation, the circuit diagram in Figure 24 illustrates the rechargeable power source 100 as a single battery cell and the electrical load 104 as a single electrical load. It will be understood that the rechargeable power source of the load handling equipment is not limited to a battery, the battery may comprise an assembly of one or more battery cells rather than a single battery cell, and the electrical load may comprise several electric motors and other components rather than a single electrical load.

[0142] [DCDC converter] The circuit may additionally include one or more DCDC converters. As shown in Fig. 25, the circuit may additionally include a filter DCDC converter 118 between the electrical load 104 and the filter circuit 116. The purpose of the filter DCDC converter 118 is to convert the voltage on the rechargeable power supply to a different voltage on the filter circuit. With one filter DCDC converter 118 for the filter circuit 116, the voltage on the rechargeable power supply and the load voltage can be the same.

[0143] The filter DC-DC converter 118 between the electrical load 104 and the filter circuit 116 can comprise a step-up converter or a step-down converter. A step-down converter is particularly advantageous when the filter circuit comprises one or more supercapacitors in parallel with the electrical load 104, since the voltage on the one or more supercapacitors is lower. The reduced voltage means that a lower rated supercapacitor or fewer supercapacitor modules in parallel are required.

[0144] The circuit may additionally include a source DCDC converter 108 between the rechargeable power source 100 and the filter circuit 116, as shown in Fig. 26. The purpose of the source DCDC converter 108 is to convert the voltage on the rechargeable power source 100 to a different voltage on the filter circuit 116. It will be understood that with the two DCDC converters 108 and 116, the rechargeable power source 100 and the electrical load 104 may be at the same voltage or at different voltages.

[0145] The source DC-DC converter 108 between the rechargeable power source 100 and the filter circuit 116 may comprise a step-up converter or a step-down converter.

[0146] [Low pass filter] A low pass filter has a cutoff frequency below which signals with frequencies are allowed to pass, while signals with frequencies above the cutoff frequency are attenuated. The filter attenuates high frequencies in the input signal, but signals below the cutoff frequency experience little attenuation.

[0147] An ideal low-pass filter would completely reject all frequencies above the cutoff frequency while allowing frequencies below the cutoff frequency to pass through the filter unchanged. The frequency response is a step function. In practice, electronic low-pass filters are not ideal filters, and the exact frequency response of the filter depends on the filter design.

[0148] [Active vs. Passive Filters] Filter circuits can be active or passive. Active filters require additional power and include an amplifying device to increase the signal strength. The gain is greater than unity and increases the power available in the signal compared to the input. Passive filters do not include an amplifying device to strengthen the signal and do not require additional power. Passive filters cannot have a net power gain and have a gain less than unity, dissipating energy from the signal such that the magnitude of the output signal has a smaller amplitude than its corresponding input signal.

[0149] Passive filter circuits may be constructed from components such as resistors, inductors, and capacitors. The advantage is that they do not require an additional power source, which makes the circuit simpler.

[0150] Active filters have the advantage that they can achieve a given transfer function in some frequency ranges without the use of inductors, which are relatively large and costly components compared to resistors and capacitors. Because no inductors are used, active filters can be made in a very compact size and do not generate or interact with magnetic fields that may be present.

[0151] [Multi-stage filter] Multi-stage filters can be constructed by "cascading" filter circuits together. The higher the order of the filter, the greater the attenuation of signals when their frequencies are above the cutoff frequency. As the order of the filter increases, the filter approaches the characteristics and behavior of an ideal filter.

[0152] Multistage active filters have the advantage of good isolation between the stages, so these characteristics are independent of the source and load impedances. In contrast, multistage passive filters are more difficult to design, because each stage must take into account the frequency-dependent loading of the previous stage.

[0153] [Filter circuit example] One way to filter a signal is an RC filter, which is a circuit with one or more resistors and one or more capacitors driven by a voltage or current source. The circuit is called "RC" because R and C are the usual symbols used for resistance and capacitance, respectively. A first-order RC circuit is the simplest type of RC circuit and comprises one resistor and one capacitor. An RC circuit for filtering current signals comprises a parallel resistor and a capacitor driven by a current source. The cutoff frequency is determined by the RC time constant of the circuit. Figure 27a shows a parallel RC circuit. A first-order RC filter can be built using a supercapacitor in parallel with the rechargeable power source 100 and the electrical load 104.

[0154] An alternative method of filtering signals is the RL filter, which is a circuit comprising one or more resistors and one or more inductors driven by a voltage or current source. The circuit is referred to as "RL" because R and L are the usual symbols used for resistance and inductance respectively. A primary RL circuit is the simplest type of RL circuit and comprises one resistor and one inductor. An RL circuit for filtering current signals comprises a parallel resistor and an inductor driven by a current source. Figure 27b shows a parallel RL circuit.

[0155] Another alternative is the RLC filter, which is an electric circuit that includes one or more resistors, one or more inductors, and one or more capacitors. A second-order RLC circuit is the simplest type of RLC circuit and includes one resistor, one inductor, and one capacitor connected in series or parallel. The circuit is called "RLC" because R, L, and C are the usual symbols used for resistance, inductance, and capacitance, respectively. Among other uses, an RLC circuit may be used as a low-pass filter. An RLC filter is described as a second-order filter because the voltage or current in the circuit may be described by a second-order differential equation. Figure 27c shows a simple RLC circuit.

[0156] Higher order passive RLC filters may also be used, for example Butterworth filters (Figure 27d).

[0157] The above circuits are all passive filters. Active low-pass filter circuits can be constructed, for example, by using operational amplifiers. Figure 27e shows an active filter circuit with an operational amplifier.

[0158] An operational amplifier is characterized by its gain-bandwidth product (GBWP), which is the product of the amplification bandwidth and the gain at which the bandwidth is measured. The gain-bandwidth product is nearly independent of the gain at which the bandwidth is measured, so that, to a rough estimate, the gain is inversely proportional to the frequency. For example, FIG. 28 shows an operational amplifier with a GBWP of 1 MHz. At a frequency of 1 MHz, the operational amplifier has a gain of 1 (0 dB), at a frequency of 100 KHz, a gain of 1000 (60 dB), and at a frequency of 1 kHz, a gain of 1000 (60 dB). The DC gain in this example is 100000 or 100 dB. This inverse proportional response coupled with a high DC gain gives the operational amplifier the characteristics of a first-order low-pass filter. The cutoff frequency is given by dividing the GBWP by the DC gain. For the operational amplifier shown in FIG. 27e, the GBWP is 1 MHz and the DC gain is 100000, so the cutoff frequency is 10 Hz. Signals at frequencies below 10 Hz are allowed to pass with maximum gain, while higher frequency signals are subjected to a lower gain.

[0159] [Transient current during lifting / lowering operation] FIG. 19 shows the transient nature of the current during lowering and lifting operations of the load handling equipment on the storage grid.

[0160] FIG. 29 shows another example of a fishing operation of the load handling apparatus. First, the grabber device 39 is lowered into the storage grid to a depth of 21 grid positions (deceleration event). The grabber device then grabs a storage container 10 of mass 30 kg and lifts it upwards to the top of the grid into a container receiving space in the load handling apparatus (acceleration event). The grabber device then lowers the storage container back down to its original position in the storage grid (second deceleration event), releases the storage container, and then lifts the grabber device upwards back to the top of the grid (second acceleration event). It can be seen from FIG. 29 that the first acceleration event in which the grabber device is lifted while loaded with a 30 kg storage container has a significantly higher average current than the second acceleration event in which the grabber device is lifted without a load. Similarly, the second deceleration event, in which the grabber device is lowered while loaded with a 30 kg storage container, has a significantly higher average current than the first deceleration event, in which the gripper device is lowered with no load.

[0161] Table 5 below lists the average current for each of the four acceleration / deceleration events shown in Figure 29, along with the peak-to-peak variation of current for that event. It can be seen that the variation is large, with the peak-to-peak variation exceeding 40 amps for the first acceleration event.

[0162] [Table 5]

[0163] [Fourier transform of the current signal] To get a better understanding of the high frequency content of the current signal, Figures 30a-d plot the Fourier transform of the current signal plotted in Figure 29. The sampling frequency was 6250 Hz, so the Fourier plot uses a scale from zero up to the Nyquist frequency of 3125 Hz. Figure 30a plots the entire Fourier transform and shows large spikes at low frequencies and some smaller spikes in the frequency range up to 1000 Hz. Figure 30b (inset) plots the same Fourier transform over the range 0-1000 Hz and amplitude up to 1, from which it can be seen that the majority of the smaller spikes occur at frequencies above 20 Hz. Figure 30c plots the same Fourier transform over the range 0-20 Hz and amplitude up to 1. It can be seen that the low frequency peaks fall below 1 Hz, with a large peak at about 9 Hz and a second largest peak at about 11 Hz. Figure 30d plots the Fourier transform in the range of 0-1 Hz, but at this resolution it is difficult to see the detailed shape of the spectrum, and a peak can be seen at about 0.08 Hz, which corresponds to a period of about 12.5 seconds, the duration of one lift and lower actuation (it can be seen from Figure 29 that the time between the start of the first deceleration event and the second deceleration event is about 12.5 seconds, and the time between the start of the first acceleration event and the second acceleration event is about 12.5 seconds).

[0164] Examining the Fourier transform of the current signal shows that most of the noise in the current is between 20 Hz and 1000 Hz, with additional spikes at 9 Hz and 11 Hz. A low pass filter at 20 Hz or 7 Hz will remove most of these transients, producing a smoother signal.

[0165] The above example demonstrates how a predetermined cutoff frequency can be determined from the Fourier transform of a signal. If the predetermined cutoff frequency is known, a filter circuit can be designed to act as a low pass filter, passing frequencies below the predetermined cutoff frequency and attenuating frequencies above the predetermined cutoff frequency.

[0166] For passive low-pass filter circuits, component specifications may be selected such that the circuit frequency is equal to a predetermined cutoff frequency. For example, in an RC filter circuit, the resistance and capacitance values ​​may be selected such that the circuit frequency is the desired cutoff frequency. In an RL filter circuit, the resistance and inductance values ​​may be selected such that the circuit frequency is the predetermined cutoff frequency. In an RLC filter circuit, the resistance, inductance, and capacitance values ​​may be selected such that the circuit frequency is the predetermined cutoff frequency.

[0167] In the case of an active low pass filter circuit using an operational amplifier, the characteristics of the operational amplifier may be selected such that the cutoff frequency of the circuit is the same as a predetermined cutoff frequency. As explained above with reference to Figure 28, as an approximation, the cutoff frequency of an operational amplifier may be calculated by dividing its GBWP by its DC gain.

[0168] [Low pass filter RC circuit] The principles of designing a low pass filter circuit with a given cutoff frequency are presented here with reference to a first order RC filter. It will be understood that this particular circuit is one of many possible implementations of the filter design and is not intended to be limiting.

[0169] Figure 27a shows a simple first-order RC filter circuit, with a resistor and a capacitor connected in parallel. The time constant of the filter is calculated from the product of the resistance and capacitance, so the cutoff frequency, f, is given by Equation 1:

[0170]

number

[0171] where R is the resistance and C is the capacitance of the circuit.

[0172] The reactance X is given by Equation 2. At higher frequencies, the reactance drops and the capacitor effectively acts as a short circuit.

[0173]

number

[0174] The low frequency components of the current signal are attenuated by the reactance of the capacitor. Instead of current passing freely through the capacitor, charge builds up on the capacitor plates. Pure DC current (the zero frequency component of the current signal) cannot pass through the capacitor at all, and must instead go through the resistor. The low frequency components are not completely blocked by the capacitor, but their amplitude is attenuated and at least a portion of the current is directed through the resistor.

[0175] The high frequency components of the current signal flow very well through the capacitor because there is very little time for the capacitor to accumulate charge before the high frequency components of the current change direction: the current is effectively shorted through the capacitor rather than flowing through a resistor.

[0176] In reality, the capacitor behaves between these two extremes because the current signal has components in a range of frequencies.

[0177] For the current signal discussed above and shown in Figure 29, examination of the Fourier transform of the current signal (shown in Figure 30) suggests that a predetermined cutoff frequency of approximately 20 Hz, or (preferably) 7 Hz, is appropriate. Equation 1 can be used to select appropriate values ​​of R and C to create a filter circuit having a circuit frequency of 20 Hz or 7 Hz.

[0178] Equation 1 can be rearranged to calculate the required capacitance (Equation 3):

[0179]

number

[0180] Using a resistor with a resistance of 3.5 mΩ, applying Equation 3 gives a desired capacitance of 2.3 F for a 20 Hz circuit and 6.6 F for a 7 Hz circuit.

[0181] [Demonstration of low-pass filtering through simulation] Figure 31 is a Simulink model of a simple RC filter circuit with a resistor and a capacitor in parallel. The 48V voltage source represents the rechargeable power supply and the resistor represents the electrical load. The resistance of the resistor is 3.5mΩ. The current signal from Figure 29 is applied through the resistor and the current signal at the rechargeable power supply is plotted.

[0182] FIG. 32 plots the current signal through the resistor and the rechargeable power supply. As calculated above, a filter circuit with a circuit frequency of 20 Hz should filter out most of the transients from the current signal. FIG. 32a is the same original current signal as in FIG. 29. FIG. 32b is the signal filtered in the rechargeable power supply using an RC filter circuit, where the circuit frequency is 20 Hz, the resistor has a resistance of 3.5 mΩ, and the capacitor has a capacitance of 2.3 Farads. It can be seen that the transients in the current through the rechargeable power supply are greatly reduced compared to the input current. The input current has a spike of 47 amps at about 6.5 seconds at the beginning of the first acceleration event, which is reduced to a much lower spike of 33 amps seen by the rechargeable power supply. This demonstrates that the use of the capacitor in the filter circuit reduces the transients and spikes in the current, and therefore reduces the aging effects on the rechargeable power supply.

[0183] As calculated above, the filter circuit at 7 Hz should filter out the transients from the current signal in the same way as the 20 Hz circuit, and also remove the peaks observed at 9 Hz and 11 Hz. Figure 32c is the filtered signal at the rechargeable power supply using an RC filter circuit, where the circuit frequency is 7 Hz, the resistor has a resistance of 3.5 mΩ, and the capacitor has a capacitance of 6.6 Farads. It can be seen that the transients in the current through the rechargeable power supply are greatly reduced compared to the input current, and even more so at the 7 Hz filter circuit frequency than at the 20 Hz filter circuit frequency. At the start of the first acceleration event, the input current spike of 47 amps at about 6.5 seconds is reduced to 26 amps seen by the rechargeable power supply. This spike is comparable to the average current of 24 amps for the first acceleration event.

[0184] Table 6 below lists the average current for each of the four acceleration / deceleration events, the peak-to-peak variation in current for that event, and the peak-to-peak variation in current after filtering at 20 Hz and 7 Hz. It can be seen that the peak-to-peak variation is significantly reduced by filtering.

[0185] [Table 6]

[0186] Figure 33a compares the load current to the current through a rechargeable power supply with a 20Hz filter circuit, and Figure 33b compares the load current to the current through a rechargeable power supply with a 70Hz filter circuit. It can easily be seen how the transients in the current signal are greatly attenuated.

[0187] [Nonlinearity of lithium-ion battery cells] FIG. 34 shows a typical discharge curve for a lithium-ion battery cell, plotting cell voltage against discharge capacity. Discharge capacity is defined as 100% minus the state of charge. A state of charge of 100% corresponds to a discharge capacity of 0%, and a state of charge of 0% corresponds to a discharge capacity of 100%. It can be seen that the discharge curve is highly nonlinear. This means that in fact a lithium-ion cell does not operate over its entire voltage range. Although the voltage range goes up to 4.2V for a single lithium-ion battery cell, in fact the highly nonlinear shape of the curve means that the battery cell spends most of its time between 3 and 4 volts. The figure shows only the indicated voltage curve. In fact the shape of the curve depends on factors such as temperature and discharge rate. Other battery cell chemistries have different maximum voltages and different discharge curves, which can also be nonlinear. This can be problematic for load handling equipment where the rechargeable power source is a battery, since the load handling equipment cannot use the full battery range.

[0188] Several lithium-ion battery cells can be arranged in series to provide power to one or more load motors. For example, 12 lithium-ion battery cells in series give a voltage range of up to 12*4.2=50.4V, which is enough to power one or more load motors at a nominal voltage of 48V. A lithium-ion cell spends most of its time operating between 36V (12×3V) and 48V (12×4V). In fact, a lithium-ion battery uses only a small fraction of its full voltage range (and therefore only a small fraction of its full energy storage).

[0189] However, in practice, when the voltage of the lithium-ion battery pack drops below a threshold voltage for powering an electrical load, the load motor does not have enough power to provide the acceleration required by the load handling device. This can happen before the lithium-ion battery is fully discharged, which means that only a portion of the useful range of the lithium-ion cells is used to provide power. Once the threshold voltage is reached, the battery can no longer provide sufficient power, and so the load handling device must be charged. For a load handling device with a 48V lithium-ion battery pack and a 48V electrical load, this threshold voltage is approximately 42.6V.

[0190] In some embodiments, the load handling equipment may need to achieve a certain acceleration to perform its function. To achieve the processing of items from the storage system to fulfill the orders, and therefore to meet the demand, the load handling equipment needs to operate on the grid with the maximum possible acceleration. The higher the acceleration of the load handling equipment operable on the grid, the faster the load handling equipment can reach the desired grid cell when removing or storing a storage container from a given stack. Conversely, the lower the acceleration of the load handling equipment operating on the grid, the longer it takes the load handling equipment to reach the desired grid cell, and therefore the more time the load handling equipment will spend removing a storage container from a given stack. As a result, an increased number of load handling equipment needs to be operable on the grid to maintain the processing of items from the storage system, and therefore to meet the demand, with a lower acceleration.

[0191] The storage system includes a control system that manages the movement of the load handling equipment on the grid. The control system keeps track of the position of each of the load handling equipment and commands the load handling equipment to move to a new location and avoids collisions. If the load handling equipment cannot achieve the required acceleration, it may not be able to make the required movement in the expected time. Other load handling equipment may need to slow down or be rerouted to avoid collisions. This makes the control even more complex and may slow down or block the route of not only the load handling equipment with insufficient acceleration, but also other load handling equipment on the grid.

[0192] Thus, in some embodiments, it may be beneficial to define a predetermined acceleration for the load handling apparatus to perform its function. This may be the linear acceleration at which the load handling apparatus moves along the track on the grid frame structure, or the acceleration at which the grabber device lifts the container from the storage system and into the container receiving space of the load handling apparatus, or both. The predetermined acceleration defines the torque requirement of the lifting drive assembly and / or drive mechanism, and thus the torque requirement of the motor. The torque requirement defines a threshold voltage. This voltage is referred to as the predetermined threshold voltage because its value is defined by the predetermined acceleration. Typically, this is referred to as the operating voltage of the electrical load. When the motor voltage drops below this predetermined threshold voltage, the load handling apparatus will not be able to achieve the predetermined acceleration. In an exemplary embodiment, for a load handling apparatus having a 48V lithium-ion battery pack and a 48V electrical load, this threshold voltage is approximately 42.6V.

[0193] Thus, the usable portion of the battery's voltage range is reduced even further. For example, a 5 kWh lithium-ion battery may only use 1.5 kWh (one third of the maximum) of its energy capacity. This is problematic because the cost and mass of the battery is high, and because only a portion of its battery capacity can be used, the battery must be charged more frequently than would otherwise be necessary. Charging requires downtime, as well as time and energy expended by the load handling equipment in traveling to and from charging stations on the storage grid.

[0194] The problem to be solved is how to operate the load handling equipment for a longer period of time before the rechargeable power source needs to be charged.

[0195] One way to increase the time between charges is to increase the voltage of the rechargeable power source. However, this is less than optimal because a higher voltage requires increased safety precautions to protect workers. A higher voltage requires higher rated components with associated higher costs. Also, increasing the voltage does not solve the problem of a rechargeable power source only operating within a portion of its useful range.

[0196] An alternative approach is to use more of the operating voltage range of the rechargeable power source by using a second power source as a “booster” to allow the energy storage system to provide sufficient power after the voltage of the rechargeable power source drops below a certain threshold voltage for powering an electrical load.

[0197] A supercapacitor may be placed in parallel with a rechargeable power source such that both the supercapacitor and the rechargeable power source provide power to the load motor at the same voltage. However, this is not ideal because only a portion of the useful voltage range of the supercapacitor is used. The cost of supercapacitors per unit of energy storage is higher than other rechargeable power sources, and several supercapacitor modules in series may be required to reach the required voltage.

[0198] FIG. 35 compares typical discharge curves of a battery and a supercapacitor. The discharge curve of the supercapacitor is an almost straight line, with the voltage dropping linearly with the discharge capacity (discharge capacity is defined as 100% minus the state of charge). The battery discharge curve is much shallower, so for the same change in voltage, the battery experiences a larger change in SOC. When the battery and spike are connected in parallel, they are exposed to the same voltage. The difference in the shape of the discharge curves means that when the parallel battery and supercapacitor experience the same voltage drop, the state of charge of the battery drops further than that of the supercapacitor, because the discharge curve of the battery is shallower than that of the supercapacitor. Thus, the supercapacitor experiences a smaller change in state of charge and only uses a smaller portion of its SOC range. Thus, a circuit with a supercapacitor and a battery connected in parallel, both of which power an electrical load, has the disadvantage of only being able to use a portion of the full SOC range of the supercapacitor.

[0199] [Supercapacitor as a booster in series with a rechargeable power source] Another way to use a supercapacitor as a power booster is to connect it in series with a rechargeable power source. Because the discharge curve of a supercapacitor is linear, its full voltage range can be used.

[0200] Because supercapacitors have a low energy density and are more expensive per unit of energy storage than other rechargeable power sources, supercapacitors with lower nominal voltages may be used. Connecting an assembly of one or more supercapacitors in series to a rechargeable power source means that the nominal voltage of the supercapacitor can be lower than that of the rechargeable power source - without the need to connect several supercapacitor cells in series to match the voltage of the rechargeable power source - and therefore fewer supercapacitor cells can be used.

[0201] Connecting the supercapacitor in series with the rechargeable power source means that, provided that the combined voltage on the supercapacitor and the rechargeable power source is equal to or greater than a predetermined threshold voltage for powering an electrical load, the load handling equipment can continue to operate even if the voltage on the rechargeable power source drops below the predetermined threshold voltage. In practice, this means that the load handling equipment can operate for longer periods between charges at a charging station.

[0202] In the example given above, for a nominal 48V lithium ion battery pack with a nominal 48V electrical load, the predetermined threshold voltage is approximately 42.6V. With the battery alone, the load handling equipment would need to be charged when the battery voltage drops to 42.6V. However, with a 5V supercapacitor in series with the battery, the load handling equipment can continue to operate until the battery voltage drops to 37.6V, at which point the combined voltage on the battery and supercapacitor, 5V+37.6V, has dropped to the predetermined threshold voltage of 42.6.

[0203] Supercapacitors with voltages of 2.7 or 5.4V are readily available on the market. Other voltages are also available.

[0204] [Peak electricity demand is short-lived] As explained above, the energy storage system of the load handling device must be able to provide sufficient power to the drive mechanism and / or lift drive assembly to complete an acceleration event. However, an acceleration event does not have a fixed power demand.

[0205] Peak demand from electrical loads occurs only for a short period of time. FIG. 36 plots the power demand from the motors powering the wheels of a load handling device as the load handling device moves on top of a storage grid. It can be seen that the peak power demand occurs at approximately 1.1 seconds and lasts only a fraction of a second. Therefore, the energy storage system needs to provide maximum power for only a short period of time. Supercapacitors are perfectly suited to provide this power boost because of their high power density but low energy density. Because the demand is for a short period of time, high energy storage capacity is not required. Supercapacitors can help meet the power demand without adding significant extra mass or cost to the energy storage system.

[0206] A deceleration event can also be seen on Figure 36 between approximately 1.3 seconds and 2 seconds. The power demand during this time is negative, meaning that the motor is acting as a generator and recovering energy from the deceleration of the load handling equipment.

[0207] The energy storage system of the load handling equipment must be able to provide power to enable the lifting drive assembly to lower and raise the grabber device to retrieve or place the storage container. As discussed above, FIG. 29 shows an example of a lifting operation of the load handling equipment. It can also be seen from FIG. 29 that the peak demand from the electrical load occurs only for a short period of time. The peak power demand for the first acceleration event occurs at about 6.5 seconds and lasts only a fraction of a second. Therefore, the energy storage system needs to provide maximum power for only a short period of time. Supercapacitors are perfectly suited to provide this power boost due to their high power density but low energy density. Because the demand is for a short period of time, high energy storage capacity is not required. Supercapacitors can help meet the power demand without adding significant extra mass or cost to the energy storage system.

[0208] [Schematic of a supercapacitor connected in series with a rechargeable power source] 37 shows a simple circuit diagram in which a supercapacitor 102 is connected in series with a rechargeable power source 100. Together, the supercapacitor and the rechargeable power source provide power to an electrical load 104. During normal operation, both the rechargeable power source 100 and the supercapacitor 102 provide power to the electrical load 104.

[0209] FIG. 37 shows a single battery cell 100, a single supercapacitor 102, and a single electrical load 104 for ease of illustration only. The rechargeable power source 100 is not limited to a battery, but can comprise multiple battery cells connected in series and / or parallel. The battery cells may be connected in series to increase the voltage (e.g., a battery with a nominal voltage of 48V can comprise 12 lithium-ion battery cells in series with a maximum voltage of 4.2V each) and / or in parallel to increase the energy storage capacity. The supercapacitor 102 can comprise multiple supercapacitors in series or parallel, in series to increase the voltage, and in parallel to increase the energy storage capacity. The electrical load 104 can comprise multiple electric motors or other components. For example, the electrical load can comprise one or more motors as part of a lifting drive assembly and one or more motors as part of a drive mechanism to drive the wheels of a load handling device.

[0210] FIG. 38 shows a circuit diagram where the rechargeable power source 100 comprises a number of battery cells connected in series, the supercapacitor 102 comprises a number of supercapacitor modules connected in series and in parallel, and the electrical load 104 comprises a number of electric motors connected in parallel.

[0211] The ground 105 may be common and all grounded components may be connected to the chassis of the load handling device.

[0212] [Controlling supercapacitor charging] The controller 120 may be used to manage the charging and discharging of the supercapacitor 102. The controller may be configured to instruct the rechargeable power source 100 to charge the assembly of one or more supercapacitor modules when the voltage on the assembly of one or more supercapacitor modules falls below a predetermined threshold supercapacitor recharge voltage.

[0213] The predetermined threshold supercapacitor recharge voltage may be defined to be sufficiently below the maximum rated voltage of the supercapacitor such that there is sufficient unused energy storage capacity to accommodate the energy recovered from the deceleration event.

[0214] The DC / DC converter 122 may be used to convert voltage between the rechargeable power source 100 and an assembly of one or more supercapacitor modules 102.

[0215] When energy is recovered from the drive mechanism and / or lift drive assembly of the load handling apparatus during a deceleration event, the controller directs the recovered energy to the assembly of one or more supercapacitor modules if the voltage on the assembly of one or more supercapacitor modules falls below a predetermined threshold supercapacitor recharge voltage.

[0216] A DC / DC converter may be used to convert voltage between the load voltage and the assembly of one or more supercapacitor modules. This may be the same DC / DC converter 122 used to convert voltage between the rechargeable power source and the assembly of one or more supercapacitor modules.

[0217] An assembly of one or more supercapacitor modules may be selected to have a power rating sufficient to receive the recovered power from the drive mechanism and / or lifting drive assembly during deceleration, and an energy storage capacity sufficient to receive and store the recovered energy from the drive mechanism and / or lifting drive assembly during one or more deceleration events, ensuring that all of the available recovered energy is captured and stored.

[0218] 39 and 40 show the control operation of the circuit. The controller 120 controls the voltage V on the rechargeable power supply. b and the combined voltage V on the rechargeable power source and the supercapacitor module. c The difference between these two voltages, V c -V b is the voltage on the supercapacitor. If the voltage on the supercapacitor falls below a predefined threshold supercapacitor recharge voltage, the controller charges the supercapacitor. The input current I in can be supplied by a rechargeable power source, or alternatively can be braking current recovered from the drive mechanism and / or lift drive assembly during a deceleration event. A DC-DC converter 122 can be used to convert the voltage of this input to supply the supercapacitors at the appropriate voltage.

[0219] Figure 39 shows the operation of the circuit when the rechargeable power source 100 is used to charge the supercapacitor 102. The arrows on Figure 39 indicate the direction of current flow. The rechargeable power source 100 provides power to the electrical load 104 and also to the supercapacitor 102 via the controller 120 and the DC-DC converter 122.

[0220] Figure 40 shows the operation of the circuit when the recovered energy from the electrical load 104 is used to charge the supercapacitor 102. The arrows on Figure 40 indicate the direction of current flow. The recovered energy from the electrical load 104 is provided to the supercapacitor 102 via the controller 120 and the DC-DC converter 122.

[0221] FIG. 41 shows in more detail one possible embodiment of the controller 120 and the DC-DC converter 122. The voltage V on the supercapacitor c -V b When the input current I falls below a predetermined threshold supercapacitor recharge voltage, the controller 120 sends a signal, which may be a square wave, to the base of the transistor 124. When the transistor 124 is activated, it reduces the input current I in The DC-DC converter 122 allows a current to flow through a first coil of the transformer 126 to ground 105. A current is induced in a second coil of the transformer 126. This current passes through a rectifier 128 and is then used to charge the supercapacitor 102. To monitor the output voltage and current from the DC-DC converter 122, a voltage and current feedback I fb and V fb is measured by the controller 120.

[0222] A switch 130 may be used to protect the supercapacitor 102 from overcharging. The controller 120 can detect when the supercapacitor voltage is too high, for example when the supercapacitor voltage exceeds a maximum supercapacitor voltage, and can then operate the switch to disconnect the power supply to the supercapacitor. Although the switch 130 is shown here between the controller 120 and the base of the transistor 124, it will be understood that the switch can be located anywhere in the circuit that allows the power supply to the supercapacitor 102 to be disconnected.

[0223] [Supercapacitor protection circuit] During normal operation, the supercapacitor 102 discharges and provides power to the electrical load 104. When the supercapacitor is fully discharged, it is no longer able to provide power. A supercapacitor protection circuit 132 may be used to ensure that the supercapacitor does not back charge after it has been fully discharged, which could cause damage to the supercapacitor.

[0224] 42 is a partial circuit diagram showing a supercapacitor protection circuit 132 that bypasses the supercapacitor 102. Under normal operation, the supercapacitor becomes charged, or partially charged, and discharges as current flows through it. When the supercapacitor is discharged, the supercapacitor protection circuit 132 allows current to bypass the supercapacitor rather than flow through it.

[0225] The supercapacitor protection circuit 132, which stops reverse charging of the supercapacitor, can include a transistor. The transistor can be controlled by a supercapacitor protection circuit controller 134. When the voltage on the supercapacitor 102 drops below zero volts, the supercapacitor protection circuit controller 134 sends a signal to the base of the transistor 132 to turn the transistor on, thus allowing current to flow through the transistor 132 instead of the supercapacitor 102. The supercapacitor protection circuit controller 134 can be a separate device or can be integrated within the same controller 120 that controls the charging of the supercapacitor.

[0226] The control law of the supercapacitor can be summarized as follows: 1. If the voltage on the supercapacitor 102 is below a predetermined threshold supercapacitor recharge voltage, the controller 120 commands the rechargeable power source 100 to charge the supercapacitor 102 through the DCDC converter 122. 2. When the voltage on the supercapacitor 102 is below a predetermined threshold supercapacitor recharge voltage, the controller 120 directs all recovered energy from the drive mechanism and / or lift drive assembly to the supercapacitor 102 through the DC-DC converter 122. 3. If the voltage on the supercapacitor 102 is less than zero, the supercapacitor protection circuit 134 activates the supercapacitor protection circuit 132 to prevent the supercapacitor 102 from back charging. 4. If the supercapacitor voltage is greater than the maximum supercapacitor voltage, the controller 120 disconnects the power supply to the supercapacitor and opens the switch 130 to protect the supercapacitor 102 from overcharging. The following is a summary of the claims as originally filed: [1] A load handling apparatus (30) for lifting and moving one or more stacked containers (10) within a storage system comprising a grid framework (14) supporting a pathway arranged in a grid pattern above a stack (12) of the containers (10), said load handling apparatus (30) comprising: i) a body (32) housing a drive mechanism operatively arranged to move said load handling apparatus (30) on said grid framework (14); ii) a lifting device comprising a lifting drive assembly and a grabber device (39) configured, in use, to releasably grip said container (10) and lift said container (10) from said stack (12) into a container receiving space (40), wherein said lifting drive assembly and / or said drive mechanism comprises at least one motor forming an electrical load (104); iii) a rechargeable power source (100); and iv) an assembly of one or more supercapacitor modules (102), a load handling apparatus (30) configured to connect an electrical load (104) across the assembly of one or more supercapacitor modules (102) and to provide electrical power to the assembly of one or more supercapacitor modules (102), and to connect the rechargeable power source (100) in parallel to the assembly of one or more supercapacitor modules (102) such that the rechargeable power source (100) is configured to provide electrical power to the assembly of one or more supercapacitor modules (102). [2] The cargo handling apparatus (30) of [1], further comprising a load DC-DC converter (110) between the assembly of one or more supercapacitor modules (102) and the electrical load (104). [3] The load handling apparatus (30) of [2], wherein the load DC-DC converter (110) between the assembly of one or more supercapacitor modules (102) and the electrical load (104) is a boost converter. [4] The cargo handling apparatus (30) of any one of [1] to [3], further comprising a source DC-DC converter (108) between the rechargeable power source (100) and the assembly of one or more supercapacitor modules (102). [5] The cargo handling apparatus (30) of [4], wherein the source DC-DC converter (108) between the rechargeable power source (100) and the assembly of one or more supercapacitor modules (102) is a step-down converter. [6] A cargo handling apparatus (30) as described in any one of [1] to [5], wherein a control device (114) is configured to vary the power supplied from the rechargeable power source (100) to the assembly of one or more supercapacitor modules (102). [7] The cargo handling apparatus (30) of [6], wherein the control device (114) is configured to instruct the rechargeable power source (100) to supply charge to the assembly of one or more supercapacitor modules (102) when the voltage of the assembly of one or more supercapacitor modules (102) falls below a predetermined supercapacitor target voltage threshold. [8] The load handling apparatus (30) of [7], wherein the predetermined supercapacitor target voltage threshold is lower than a maximum rated voltage of an assembly of the one or more supercapacitor modules (102). [9] The cargo handling apparatus (30) of any one of [6] to [8], wherein the control device (114) is configured to instruct the rechargeable power source (100) to supply charge to the assembly of one or more supercapacitor modules (102) at a predetermined threshold current for battery balancing.

[10] The load handling equipment (30) of any one of [6] to [8], wherein the control device (114) is configured, in use, to periodically disconnect the rechargeable power source (100) from the assembly of one or more supercapacitor modules (102) so that the rechargeable power source (100) experiences periods of low current drain during which no charge is supplied to the assembly of one or more supercapacitor modules (102).

[11] The load handling apparatus (30) of any one of [1] to

[10] , further comprising an energy recovery circuit (112) for transferring recovered energy from the drive mechanism and / or the lifting drive assembly to the assembly of one or more supercapacitor modules (102), the energy recovery circuit (112) comprising a diode or a transistor.

[12] The load handling apparatus (30) of any one of [1] to

[11] , wherein the assembly of one or more supercapacitor modules (102) has a lower internal resistance than the rechargeable power source (100).

[13] The load handling apparatus (30) of any one of [1] to

[12] , wherein the electrical load (104) comprises a first portion and a second portion, the first portion of the electrical load (104) comprising a motor power load, and the second portion of the electrical load comprises a non-motor power load (106).

[14] The load handling apparatus (30) of

[13] , wherein the rechargeable power source (100) is configured to supply charge to the non-motor power load (106).

[15] The load handling apparatus (30) of any one of [1] to

[14] , wherein the assembly of one or more supercapacitor modules (102) is configured as a primary power supply for the load handling apparatus (30) and the rechargeable power source (100) is configured as an auxiliary power supply for providing power to the primary power supply.

[16] The cargo handling apparatus (30) of

[15] , wherein the control device (114) is configured to instruct the rechargeable power source (100) to provide power directly to the electrical load (104) when the voltage on the assembly of the one or more supercapacitor modules (102) falls below a predetermined supercapacitor voltage threshold.

[17] The load handling apparatus (30) of any one of [1] to

[16] , wherein an assembly of the one or more supercapacitor modules (102) is distributed around the outside of a container receiving recess (40) in the body (32) of the load handling apparatus (30), between an outer wall (42) and an inner wall (44) of the load handling apparatus (30).

[18] The load handling apparatus (30) of any one of [1] to

[17] , wherein the assembly of one or more supercapacitor modules (102) comprises a capacitor, a supercapacitor, an ultracapacitor, a lithium capacitor, an electrochemical double layer capacitor, an electric double layer capacitor, a pseudocapacitor, or a hybrid capacitor.

[19] The load handling apparatus (30) of any one of [1] to

[18] , wherein the rechargeable power source (100) comprises a lithium ion battery, a lithium ion polymer battery, a lithium air battery, a lithium iron battery, a lithium iron phosphate battery, a lead acid battery, a nickel cadmium battery, a nickel metal hydride battery, a nickel zinc battery, a sodium ion battery, a sodium air battery, a thin film battery, a solid state battery, or a smart battery carbon foam based lead acid battery.

[20] A storage system comprising a grid framework (14) supporting a pathway arranged in a grid pattern above a stack (12) of containers (10), and a plurality of load handling apparatus (30) as defined in any one of [1] to

[19] .

[21] The storage system of

[20] , further comprising one or more supercapacitor charging stations located at a grid location above an access point, within which an assembly of the one or more capacitor modules (102) on the load handling device (30) is charged by one of the one or more supercapacitor charging stations during a lifting or lowering operation.

[22] The storage system of

[21] , wherein the one or more supercapacitor charging stations are inductive supercapacitor charging stations.

[23] The storage system of any one of

[20] to

[22] , wherein a control device (114) on the load handling device (30) is configured to instruct the assembly of one or more supercapacitor modules (102) to charge the rechargeable power source (100).

[24] The storage system of any one of

[20] to

[23] , wherein the controller (114) is configured to instruct the one or more supercapacitor modules (102) to supply charge to the rechargeable power source (100) at a predetermined threshold current for battery balancing.

[25] A fulfillment center comprising a storage system described in any one of

[20] to

[24] .

[26] The temperature inside the fulfillment center is: Ambient temperature above 4°C, Refrigeration temperatures between substantially 0°C and substantially 4°C, or The fulfillment center described in

[25] , wherein the refrigeration temperature is any temperature between substantially -25°C and substantially 0°C.

Claims

1. 1. A load handling apparatus (30) for lifting and moving one or more stacked containers (10) within a storage system comprising a grid framework (14) supporting a path arranged in a grid pattern above a stack (12) of the containers (10), said load handling apparatus (30) comprising: i) a body (32) housing a drive mechanism operatively arranged to move said load handling apparatus (30) over said grid framework (14); ii) a lifting device comprising a lifting drive assembly and a grabber device (39) configured in use to releasably grip the container (10) and lift the container (10) from the stack (12) into a container receiving space (40), wherein the lifting drive assembly and / or the drive mechanism comprises at least one motor forming an electrical load (104), the electrical load (104) comprising a first portion and a second portion, the first portion of the electrical load (104) comprising a motive power load and the second portion of the electrical load comprising a non-motive power load (106); iii) a rechargeable power source (100); and iv) an assembly of one or more supercapacitor modules (102), the electrical load (104) is connected across the assembly of one or more supercapacitor modules (102), the rechargeable power source (100) is connected in parallel to the assembly of one or more supercapacitor modules (102) such that the rechargeable power source (100) is configured to provide power to the assembly of one or more supercapacitor modules (102), and the assembly of one or more supercapacitor modules (102) is configured to supply power to the non-motive power load (106); a controller (114) configured to vary the power supplied from the rechargeable power source (100) to the assembly of one or more supercapacitor modules (102); 13. The load handling apparatus of claim 12, wherein the control device is configured to command the rechargeable power source to power the assembly of one or more supercapacitor modules at a predetermined threshold current for battery balancing.

2. The load handling apparatus (30) of claim 1, further comprising a load DCDC converter (110) between the assembly of one or more supercapacitor modules (102) and the electrical load (104).

3. 3. The load handling apparatus of claim 2, wherein the load DCDC converter between the assembly of one or more supercapacitor modules and the electrical load is a boost converter.

4. 4. The load handling apparatus (30) of claim 1, further comprising a source DC-DC converter (108) between the rechargeable power source (100) and the assembly of one or more supercapacitor modules (102).

5. 5. The load handling apparatus of claim 4, wherein the source DCDC converter between the rechargeable power source and the assembly of one or more supercapacitor modules is a step-down converter.

6. 2. The load handling apparatus of claim 1, wherein the controller is configured to instruct the rechargeable power source to supply power to the assembly of one or more supercapacitor modules when a voltage of the assembly of one or more supercapacitor modules falls below a predetermined supercapacitor target voltage threshold.

7. The load handling apparatus (30) of claim 6, wherein the predetermined supercapacitor target voltage threshold is less than a maximum rated voltage of the assembly of one or more supercapacitor modules (102).

8. A load handling apparatus (30) for lifting and moving one or more stacked containers (10) within a storage system comprising a grid framework (14) supporting a path arranged in a grid pattern above a stack (12) of the containers (10), said load handling apparatus (30) comprising: i) a body (32) housing a drive mechanism operatively arranged to move said load handling apparatus (30) over said grid framework (14); ii) a lifting device comprising a lifting drive assembly and a grabber device (39) configured in use to releasably grip the container (10) and lift the container (10) from the stack (12) into a container receiving space (40), wherein the lifting drive assembly and / or the drive mechanism comprises at least one motor forming an electrical load (104), the electrical load (104) comprising a first portion and a second portion, the first portion of the electrical load (104) comprising a motive power load and the second portion of the electrical load comprising a non-motive power load (106); iii) a rechargeable power source (100); and iv) an assembly of one or more supercapacitor modules (102), the electrical load (104) is connected across the assembly of one or more supercapacitor modules (102), the rechargeable power source (100) is connected in parallel to the assembly of one or more supercapacitor modules (102) such that the rechargeable power source (100) is configured to provide power to the assembly of one or more supercapacitor modules (102), and the assembly of one or more supercapacitor modules (102) is configured to supply power to the non-motive power load (106); a controller (114) configured to vary the power supplied from the rechargeable power source (100) to the assembly of one or more supercapacitor modules (102); 1. The load handling apparatus of claim 1, wherein the control device is configured, in use, to periodically disconnect the rechargeable power source from the assembly of one or more supercapacitor modules so that the rechargeable power source experiences periods of low current drain during which no power is supplied to the assembly of one or more supercapacitor modules.

9. 9. The load handling apparatus (30) of claim 1, further comprising an energy recovery circuit (112) for transferring recovered energy from the drive mechanism and / or the lifting drive assembly to the assembly of one or more supercapacitor modules (102), the energy recovery circuit (112) comprising a diode or a transistor.

10. 10. The load handling apparatus (30) of any one of claims 1 to 9, wherein the assembly of one or more supercapacitor modules (102) has a lower internal resistance than the rechargeable power source (100).

11. The load handling apparatus (30) of claim 1, wherein the rechargeable power source (100) is configured to power the non-motor power load (106).

12. 12. The load handling apparatus (30) of claim 1, wherein the assembly of one or more supercapacitor modules (102) is configured as a primary power supply for the load handling apparatus (30) and the rechargeable power source (100) is configured as an auxiliary power supply for providing power to the primary power supply.

13. 13. The load handling apparatus (30) of claim 12, wherein the controller (114) is configured to command the rechargeable power source (100) to provide power directly to the electrical load (104) when a voltage across the assembly of the one or more supercapacitor modules (102) falls below a predetermined supercapacitor voltage threshold.

14. 14. The load handling apparatus (30) of claim 1, wherein an assembly of the one or more supercapacitor modules (102) is distributed around the outside of a container receiving recess (40) in the body (32) of the load handling apparatus (30), between an outer wall (42) and an inner wall (44) of the load handling apparatus (30).

15. 15. The load handling apparatus (30) of any one of claims 1 to 14, wherein the assembly of one or more supercapacitor modules (102) comprises a capacitor, a supercapacitor, an ultracapacitor, a lithium capacitor, an electrochemical double layer capacitor, an electric double layer capacitor, a pseudocapacitor, or a hybrid capacitor.

16. 16. The load handling apparatus (30) of any one of claims 1 to 15, wherein the rechargeable power source (100) comprises a lithium ion battery, a lithium ion polymer battery, a lithium air battery, a lithium iron battery, a lithium iron phosphate battery, a lead acid battery, a nickel cadmium battery, a nickel metal hydride battery, a nickel zinc battery, a sodium ion battery, a sodium air battery, a thin film battery, a solid state battery, or a smart battery carbon foam based lead acid battery.

17. a grid framework (14) for supporting pathways arranged in a grid pattern above the stack (12) of containers (10); a plurality of load handling devices (30) for lifting and moving one or more stacked containers (10) within the storage system comprising a grid framework (14) supporting a path arranged in a grid pattern above a stack (12) of the containers (10), the load handling devices (30) comprising: i) a body (32) housing a drive mechanism operatively arranged to move said load handling apparatus (30) over said grid framework (14); ii) a lifting device comprising a lifting drive assembly and a grabber device (39) configured in use to releasably grip the container (10) and lift the container (10) from the stack (12) into a container receiving space (40), wherein the lifting drive assembly and / or the drive mechanism comprises at least one motor forming an electrical load (104), the electrical load (104) comprising a first portion and a second portion, the first portion of the electrical load (104) comprising a motive power load and the second portion of the electrical load comprising a non-motive power load (106); iii) a rechargeable power source (100); and iv) an assembly of one or more supercapacitor modules (102), the electrical load (104) is connected across the assembly of one or more supercapacitor modules (102), the rechargeable power source (100) is connected in parallel to the assembly of one or more supercapacitor modules (102) such that the rechargeable power source (100) is configured to provide power to the assembly of one or more supercapacitor modules (102), and the assembly of one or more supercapacitor modules (102) is configured to supply power to the non-motive power load (106); The storage system comprises: The storage system further comprises one or more supercapacitor charging stations located at grid locations above an access point, within which an assembly of one or more supercapacitor modules (102) on the load handling device (30) is charged by one of the one or more supercapacitor charging stations during a lifting or lowering operation.

18. 20. The storage system of claim 17, wherein the one or more supercapacitor charging stations are inductive supercapacitor charging stations.

19. 19. The storage system of claim 17 or 18, wherein a control device (114) on the load handling device (30) is configured to command the assembly of one or more supercapacitor modules (102) to charge the rechargeable power source (100).

20. 20. The storage system of any one of claims 17 to 19, wherein the controller (114) is configured to instruct the one or more supercapacitor modules (102) to supply power to the rechargeable power source (100) at a predetermined threshold current for battery balancing.

21. A fulfillment center comprising a storage system according to any one of claims 17 to 20.

22. The temperature inside the fulfillment center is Ambient temperature above 4°C, a refrigeration temperature between substantially 0° C. and substantially 4° C.; or 22. The fulfillment center of claim 21, wherein the refrigeration temperature is anywhere between substantially -25°C and substantially 0°C.

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