Variable Load Shape Clamping Pressure Control

Abstract

A material handling clamp having a proportional relief valve that delivers pressurized fluid to a clamp arm that grips a load, and a controller configured to receive load shape data and variably control the proportional relief valve to provide a target clamping force.An attachment for a material handling vehicle, the attachment comprising a pair of opposing clamp arms configured together to selectively grip a load, a proportional relief valve that can selectively and continuously adjust pressurized fluid to at least one of the clamp arms to provide a clamping force to a gripped load, and a controller configured to receive load shape data, calculate a target clamping force using the load shape data, and variably control the proportional relief valve to provide the target clamping force.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 63 / 303,782, filed January 27, 2022, the contents of which are incorporated by reference in their entirety herein. [Background technology]

[0002]

[0002] This disclosure relates to improvements in clamps that are typically mounted on lift trucks, automated guided vehicles (AGVs), or other industrial vehicles for clamping and steering loads such as paper rolls, tissue rolls, industrial towel rolls, and the like.

[0003]

[0003] Clamp attachments such as pivoting arm roll clamps adapted for mounting on lift trucks and other vehicles are widely used to handle loads of different shapes, e.g., rolls of paper products such as newsprint and kraft paper, and other materials, each having different diameters and lengths. Pivoting arm roll clamps allow for gripping and releasing rolls of paper or other cylindrical loads from either a long arm / short arm configuration or an even arm configuration. Typically, roll clamps are pivotable to engage, transport and position a roll with the longitudinal axis of the roll either vertical or horizontal. When the rolls lie on a surface with their axes horizontal, it is preferred to use a long arm / short arm configuration, in which the upper arms of the horizontally oriented clamp attachment extend further forward of the lift vehicle than the lower arms, so that the upper arms can clear the roll without the need for the lower arms to push under the roll, which could cause the roll to roll away from the clamp, and so that the clamp pads at the ends of the upper and lower arms can engage the roll at diametrically opposite positions. On the other hand, when the rolls are transported or stacked with their longitudinal axes vertical, it is often preferred to use an equal arm configuration, in which the arms extend equally forward of the lift vehicle on either side of the roll, so that both arms can be easily inserted between closely adjacent rolls without damaging them. However, even when gripping or releasing vertical rolls, it may be useful to use a long arm / short arm configuration when gripping or releasing a roll from a position against a wall or other surface.

[0004]

[0004] One recurring problem with clamps such as pivot arm clamps due to the deformable nature of the material being gripped and lifted is that they can easily damage the load if the clamping pressure is too strong. This problem is exacerbated by the fact that clamps are designed to handle rolls of different shapes. For example, the clamping pressure applied by the clamp pads of a pivot arm clamp varies depending on the position of the arm, so it is often difficult to apply the precise clamping force needed to reliably grip the roll without damaging it.

[0005]

[0005] Therefore, what is needed are improved devices, systems, and methods for securely gripping loads without damaging them. [Brief description of the drawings]

[0006] [Figure 1] 1 is a simplified schematic diagram of an exemplary clamp gripping a load in an orientation. [Diagram 2] 1 is a simplified schematic diagram of an exemplary clamp gripping a load in another orientation. [Diagram 3] 13 is a simplified schematic diagram of an exemplary clamp gripping a load in yet another orientation. [Figure 4] FIG. 1 illustrates an exemplary clamp used to clamp a roll of the largest diameter the roll clamp is capable of and a roll of the smallest diameter the roll clamp is capable of. [Figure 5A] FIG. 5 illustrates the clamping force as a function of load shape for the roll clamp of FIG. 4 corresponding to when the short arm of the clamp is in a fully extended or fully retracted position. [Figure 5B] FIG. 13 illustrates clamping force as a function of load shape for an equal arm roll clamp as a function of roll diameter. [Figure 6] FIG. 1 illustrates an example hydraulic circuit having a proportional relief valve that can vary the target clamping force for gripping a load based on the load's shape. [Figure 7]FIG. 2 illustrates a clamp arm gripping multiple items at once, with the center of gravity of one of the items extending beyond the clamp contact pad. [Figure 8A] 11A-11C illustrate an exemplary clamp tilt adjustment to counteract tilt of a load relative to a vehicle. [Figure 8B] FIG. 8B is another view similar to FIG. 8A. [Figure 9A] FIG. 1 illustrates an exemplary clamp holding a load between spaced arms with a width "B" and a center of gravity HCG. [Figure 9B] FIG. 9B is another view similar to FIG. 9A. [Figure 10A] FIG. 9C illustrates an exemplary loss of clamping force efficiency as a function of HCG shown in FIGS. 9A and 9B. [Figure 10B] FIG. 10B is another view similar to FIG. 10A. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007]

[0015] 1 shows an exemplary roll clamp used to illustrate the systems and methods disclosed herein, which can alternately grip rolls 10 or 12 of different shapes, e.g., diameters A or B, respectively, which are engaged by a short arm 14 and a long arm 16, both at a horizontal axis or "bilge" position, each arm having a respective engaging clamping surface 14a, 16a of the type described above. Clamp arms 14 and 16 are pivotally mounted to a frame assembly 22 by respective pivot pins, such as 14b and 16b, to allow for opening and closing of the clamp arms by hydraulic cylinders (not shown), although in some cases the clamp arms may be slidably movable towards and away from each other to allow for opening and closing.

[0008]

[0016] If it is anticipated that the rolls will also be handled with their axes extending vertically, the frame assembly 22 may be equipped with a worm drive pivot motor, such as 24, which can selectively pivot the frame assembly 22, and thereby the clamp arms 14 and 16, to a horizontally spaced orientation about a forwardly extending pivot axis 26 for picking up or placing a vertically oriented roll, as shown in FIG. 2. Or, as yet another alternative, the frame assembly may be equipped with a forward pivoting appender, such as 28, which can selectively pivot the frame assembly 22 forward 90 degrees by extension of a hydraulic cylinder, such as 28, to allow the clamp arms to pick up or place a horizontal roll 12 from above, as illustrated in FIG. 3. In such a case, the pivot mechanism 24 may also be operable to pivot the clamp arms and rolls horizontally about the now vertically extending axis 26 shown in FIG. 3.

[0009]

[0017] Unequal length clamp arm arrangements often encounter certain problems when trying to handle a roll, for example, sometimes the roll is so low density and soft that it can cause a very large flat deformation at the bottom of the tissue roll when it is in the "bilge" position. The larger the flat deformation of the tissue roll, the shorter the lower clamp arm 14 and the longer the upper clamp arm 16 must be to clamp the roll 12 substantially diametrically in the "bilge" position. This means that the longer upper clamp arm 16 must reach further around the roll to clamp the roll on its diameter B. Thus, when approaching the roll, the upper clamp arm 16 must open wider to avoid the roll in the "clearance" position, limiting the maximum roll diameter that can be engaged by the clamp. Furthermore, the longer clamp arm is also more difficult to position to reach around the roll when the roll is in a vertical position, a problem that is particularly acute when it is desired to clamp a small diameter roll, making it difficult to clamp both large and small diameter rolls using the same clamp.

[0010]

[0018] Instead of the unequal length clamp arm arrangements described above, equal length clamp arm arrangements have also been used to handle high density paper rolls. In such equal arm arrangements, due to the absence of the lower short arms 14, handling of lower density rolls in a horizontal "bilge" configuration may be more susceptible to roll damage as the tissue roll's flat deformation 25 increases. This is because the equal length lower clamp arms may need to be forced into the area between the roll's flat deformation 25 and the support bed to reach a substantially vertical clamp roll diameter between the upper and lower clamping faces of the equal length clamp arm arrangement. The risk of damage caused by such forced lower clamp arm insertion may be higher for low density rolls.

[0011]

[0019] In either situation, a pivoting roll clamp, in either a short-arm-long-arm configuration or an equal-arm configuration, generates a clamping force that is a function of both the open arm position (roll diameter) and the clamping pressure. Due to the geometry of the paper roll clamp, the force generated varies with arm position, as can be seen in Figure 4. Traditionally, pressure has been controlled by a single relief valve with a single fixed setting, typically set at the maximum design pressure. This generates clamping force values ​​over a range of different roll diameters, as shown in Figures 5 and 6, as further explained below.

[0012]

[0020] This method of roll handling (fixed pressure setting, variable diameter) can result in over or under clamping of rolls at diameters other than the designed operating diameter. To address this issue and apply accurate clamping force for all roll diameters, the improved pivot arm clamp preferably uses a proportional pressure relief valve controlled by an embedded controller to continuously vary the pressure to a pre-set value obtained from an internal or external source. An example of an external source could be a Warehouse Management System (WMS). Load details communicated to the attachment control system can be used to directly calculate the optimum clamping force for the load being handled.

[0013]

[0021] An example of an internal source is a table contained within the system controller. In this example, the sensor readings can determine the load specifications, which can be utilized by the attachment controller to derive an optimized clamping force by referencing the table. The sensor measurements can also be utilized to inform the operator or provide feedback information to the host AGV (automated guided vehicle) when an ideal handling procedure (e.g., ideal contact pad positioning, etc.) is achieved. They may also be employed to further optimize the clamping force during non-ideal handling procedures. This is particularly important in human-operated applications to compensate for expected variations during approaching and engaging the load.

[0014]

[0022] In both the external and internal cases, the clamping pressure delivered to the attachment is calculated based on the specified force, arm position, and clamp geometry. Proportional relief is then used to adjust the pressure to achieve the calculated value during the clamping process.

[0015]

[0023] In addition to calculating optimized clamping forces for various load types, sizes, and weights, the system described herein can monitor, communicate, and maintain optimized clamping forces during all aspects of material handling, including initial load contact, load lifting, transportation, placement, etc. These handling scenarios will result in variations in the applied clamping force that must be accounted for to achieve optimal handling performance and reduce load damage.

[0016]

[0024] With reference to FIG. 5A, for example, clamp force characteristics (in Newtons) are shown for a particular clamp as a function of i) clamp pressure (y-axis), ii) roll diameter (x-axis), and iii) clamp configuration (two curves). For example, assume that the clamp attachment whose force characteristics are shown in this figure is used to grip a load weighing 2000 kg and is in a short arm open configuration meaning that the short arm is in the position shown in FIG. 1. Also assume that the load has a diameter of 1200 mm. Also assume that the clamp attachment has or has been given data indicating that the clamp force factor (CFF) is 2.3 as shown in this figure. This latter measure is a scaling factor used to determine the target clamp force, measured based on the particular characteristics or type of load, e.g., newspaper, tissue, etc. Specifically, for a 2000 kg load, at a gravitational acceleration of 9.8 m / s^2 and a clamp force factor of 2.3, the target clamp force would be 45,080 Newtons (mass x gravity x CFF). The force characteristic in Figure 5A shows that a roll diameter of 1200 mm is associated with 80,000 Newtons at maximum pressure. Therefore, using a proportional relief valve to reduce the clamping force to approximately 90 bar (160 bar x 45 / 80) provides a target gripping force of only 45,080 Newtons.

[0017]

[0025] Referring to FIG. 5B, an equal arm clamp can be used as well, in which case there may be only a single clamping force characteristic. For example, assume that an equal arm clamp is used to grip a 4,000 kg load with a diameter of 950 mm and has a CFF of 1.5. In view of the table shown in FIG. 5B, the target clamping force is calculated to be 58,800 Newtons (4000×9.8×1.5), and a clamping pressure of 118 bar is selected (160 bar×58,800 / 80,000).

[0018]

[0026] Those skilled in the art will appreciate that the curves shown in Figures 5A and 5B are exemplary, and that different clamps of various configurations will exhibit different characteristics. Additionally, for example, while Figure 5A shows only two curves and Figure 5B shows only one curve, in some embodiments a different number of curves may be employed, with each curve reflecting a different articulation position of the two arms. That is, in a long arm-short arm configuration, the short arm may be in a position other than a fully open or fully closed position. Similarly, some even arm clamps may have different force characteristics based on the angular position of the arms relative to the mast of the vehicle that grips the load.

[0019]

[0027] The clamping force coefficients may be provided to the disclosed clamps in any suitable manner, along with any other load information, such as load type, load height (or width), load diameter, weight, etc., used to determine the target clamping force. As one example, the clamping force coefficients may be stored in a table within the clamp or in a memory of the vehicle to which the clamp is attached. In other embodiments, such data may be provided to the clamps wirelessly, for example, by a warehouse management system that manages the operation of the AGV.

[0020]

[0028] In some other embodiments, particularly where multiple items are being gripped as a single load, the target clamping force may be based on the received density, i.e., the disclosed clamp attachment may receive information regarding the load shape, e.g., the height (often referred to as width) and load diameter of the individual items in the load, as well as the load density and number of individual items being gripped, after which the load weight may be calculated for use in tables such as those disclosed in Figures 5A and 5B.

[0021]

[0029] Some embodiments may also include sensors on the clamp that are used to measure load parameters such as diameter, height, number of items, etc. These sensors may be integrated into load engaging surfaces such as contact pads, arm position sensors, pressure transducers, etc. Also, in some embodiments, the disclosed attachments may be equipped with sensors such as load weight sensors capable of detecting the weight of the load. Information from these sensors may be used for several purposes. The disclosed clamps, for example, in some embodiments, may use such sensing information to perform clamp calculations themselves, i.e., the clamp may automatically adjust its clamping pressure based on the geometry received from its own sensors instead of information that it may have to obtain from a database, a driver, a warehouse management system, etc. Alternatively, such information may be obtained by the clamp from some other source and used to verify that information related to load geometry or other load data is correct. If the information is incorrect, a notification may be issued and / or the clamping operation may be aborted.

[0022]

[0030] In this regard, some disclosed embodiments may employ feedback to verify and / or adjust the target clamping force and / or the speed at which the target clamping force is realized. For example, the hydraulic inlet and output pressures of the actuator may be measured and used to provide feedback of the actual clamping force. Similarly, in some embodiments, optimal clamping force may be achieved by first continuously feedback monitoring the stabilization of the clamp actuator, arm movement, and minimum clamp generation time (e.g., limited to the speed at which the maximum clamping pressure can be reached) based on the expected load shape. Such feedback significantly minimizes the time to generate the clamping force and reduces the likelihood of exceeding the target clamping force, thereby reducing the risk of damage to the load.

[0023]

[0031] Also, in some embodiments, the use of sensors as described above may be employed to sense when a clamp pad approaches or contacts a load and prevent any further movement of that arm until the other arm reaches the same position, thus preventing damage from the load sliding on the ground if the vehicle is not completely close to the load.

[0024]

[0032] FIG. 6 illustrates an exemplary hydraulic circuit 100 that can proportionally adjust clamp pressure. Specifically, the circuit 100 can independently direct fluid from one or more reservoirs (not shown) to a pair of left arm cylinders 102, a pair of right arm cylinders 104, a pair of tilt cylinders 106, and a swing drive assembly 108. The hydraulic circuit 100 also preferably includes a first proportional directional control valve 110 that regulates flow to the pair of left arm cylinders 104, and a second proportional directional control valve 112 that regulates flow to the pair of left arm cylinders 104. The proportional directional control valve 114 regulates flow to the tilt cylinders 106, and the proportional directional control valve 116 regulates flow to the swing drive assembly. A system proportional relief control valve 124 regulates pressure to all hydraulic elements in the circuit 100. In some embodiments, the proportional directional control valves 110, 112, 114, 116 are electronically controlled using a pilot assistance circuit 118 and a transducer 120. Preferably, operation of the clamps described herein, e.g., controlling transducers, performing calculations, etc., may be performed using a controller 122 suitably mounted on the attachment, although in some embodiments a controller mounted on the vehicle or elsewhere may be used that simply sends signals to hydraulic / electrical components on the attachment to control operation of the attachment.

[0025]

[0033] In some embodiments, the disclosed attachment may make adjustments to the initial calculations described with respect to Figures 5A and 5B. As an example, referring to Figure 7, an arrangement is shown in which a load 132 with three identical units 134a, 134b, and 134c is gripped by an attachment with a pair of clamp arms 136 (only one shown). The clamp arms 136 have contact pads 138 that grip the entire load, but as can be seen in this figure, the units 134 have a center of gravity beyond the location where the contact pads 38 grip the units 134. (Note that the tips of the clamp arms 136 are flared and bent away from the load). In this situation, the item 134a may tend to tip outward even with a target clamping force calculated according to Figures 5A or 5B, due to a moment about its right-side nadir. Using the received load shape and / or sensor data, the attachment disclosed in these embodiments can calculate the minimum clamping force correction that needs to be added to the target clamping force calculated using the curve as described above to counteract this moment.

[0026]

[0034] Also, some embodiments of the disclosed clamps may take into account clamp force efficiency (defined as the resultant clamp force divided by the actuator force) in calculating the target clamp force to adjust arm-to-frame engagement and / or the location of the effective load center. For example, with reference to FIGS. 9A and 9B, a clamp attachment may grip a load having a center of gravity distance HCD at width "B". As the load center extends, the reaction load on the bearings supporting the clamp arms increases, resulting in a decrease in clamp force efficiency, as shown in FIG. 10A. Similarly, with reference to FIG. 10B, at a larger open range "B", arm-to-frame engagement decreases, resulting in an increase in reaction load on the bearings and a decrease in clamp force efficiency. This loss in efficiency may be used to adjust the pressure supplied to the actuators 102, 104 to ensure that the pressure supplied achieves the desired target clamp force. Non-cylindrical loads may be handled by linear motion clamps (sliding arm clamps).

[0027]

[0035] In some preferred embodiments, the disclosed attachments may include tilt compensation. Specifically, when a counterbalanced load is applied to the system, the deflection of various track components (track chassis, mast, and attachment) may cause the counterbalanced load to tilt forward / backward, and this undesired tilt may adversely affect positioning when releasing the load. (FIG. 8A). Thus, in these embodiments, an appender or auxiliary tilt function may be activated to achieve good load orientation when positioning and releasing the load (FIG. 8B). In these embodiments, an accelerometer on the attachment may provide the necessary feedback to both detect the undesired orientation and correct it. For example, if the target position is 0 degrees (vertical) and the weight of the load causes the vehicle's mast to deflect 2 degrees forward, the disclosed system and method may detect the difference and automatically adjust the tilt position -2 degrees to compensate.

[0028]

[0036] Gravity can also adversely affect the clamping forces on the load as it flips and rotates due to the fact that gravity can pull the load downward on one clamp arm while pulling it away from the other. This can cause the clamp arms to perform undesirable asynchronous arm movements. The same can be true for acceleration forces when moving a load, where the frictional forces on one arm vary relative to the other. Thus, in some embodiments of the disclosed clamp attachment, the positional synchronization of the arms may be maintained regardless of the clamp orientation, which accounts for the variations in gravity assist / resistance and internal friction, and is done by adjusting the pressure / flow to one or more arm actuators using feedback from the arm position sensors.

[0029]

[0037] In some embodiments, the "oil demand" signal provided by the controller 122 also includes a pump motor speed demand. When combined with load-sensing pressure transducers mounted on the attachment hydraulics, this implements a variable speed, fixed displacement, pressure compensated hydraulic system that can optimize energy usage by limiting pump output flow to only what is required to meet pressure demand.

[0030]

[0038] In some embodiments, the disclosed attachment may be configured for three primary modes of operation. A first calibration mode may be used to allow for semi-automatic calibration of an attached rotary encoder by actuating the attachment's functions through their maximum range of motion and monitoring the pressure input to determine when the range of each function is reached. A second mode may provide an automatic mode of operation which may be the normal mode of operation of the attachment. A third manual operation mode allows for direct manual control of the attachment and may in some embodiments be used primarily for troubleshooting, diagnostics, and error recovery.

[0031]

[0039] As discussed above, the disclosed clamping attachments and their methods of operation provide improved clamping force control that reduces or minimizes damage to the load being gripped. Additionally, utilizing the advanced clamping force control system disclosed herein reduces stresses induced within the attachment structure and provides a longer life for the attachment by minimizing the clamping force to only that required to properly handle the load.

[0032]

[0040] It is recognized that the terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not as terms of limitation, and that in the use of such terms and expressions there is no intention to exclude equivalents of the features illustrated and described or portions thereof, the scope of the invention being defined and limited only by the claims which follow.

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