Steam safety system and method

Abstract

A steam generating system 14 for receptacle cleaning and method are disclosed. The system comprises a heater 66 to heat water to generate steam; a steam outlet 42 to supply steam to a head unit of the

Description

Background The present technique relates to the field of steam generation. More particularly, the present technique relates to safety techniques for a steam generation apparatus. Throughout the day, people who enjoy several beverages, including but not limited to coffee, can be concerned by the residue left by the drink in the receptacle after consumption. When a new beverage is poured into the same receptacle, it is likely a person will want to wash the receptacle before use. Current methods to remove residues in receptacles include handwashing the vessel with water, which may include the use of a utensil and / or detergent; and placing the vessel in a conventional dishwashing appliance where it will be cleaned once its cycle is initiated. These cleaning techniques typically make use of water as a cleaning fluid, possibly with the addition of a detergent such as washing-up liquid or dishwasher detergent. Alternative cleaning techniques involve the use of steam as a cleaning fluid which has a number of advantages compared to the use of water. For example, given its temperature, steam is a particularly effective at removing dirt and grease from surfaces. Additionally, steam is able to sanitise surfaces without the need for additional chemical agents and by using steam, it may be possible to reduce the volume of water used compared to cleaning methods that make use of liquid water. Further, it may be possible to benefit from reduced drying times following steam cleaning. However, the use of steam also poses safety challenges. One of the primary dangers of steam use is the risk of burns if human skin is exposed to the high temperature steam. Even relatively short-lived exposure to steam can cause damage and so care should be taken when carrying out steam cleaning to reduce the risk of a user coming into contact with the steam. This concern may be exacerbated where the steam cleaning is carried out by untrained or non-specialist users. Additionally, associated with the generation of steam is a risk of inadvertently creating a pressurised system (or similarly over-pressurising a steam system beyond an intended pressure). Such pressurisation may result from malfunctioning equipment and / or blockages in steam escape mechanisms and can increase the chance of equipment failure in a potentially dangerous fashion. Summary Viewed from a first aspect, there is provided a system comprising a steam generating apparatus for a receptacle cleaning device, the steam generating apparatus comprising: a heater to heat water to generate steam; a steam provision path for supplying steam to a head unit of the receptacle cleaning device; a drainage path, separate from the steam provision path, to allow steam to escape the steam generating apparatus without passing through the head unit; one or more valves arranged to control the flow of steam along the steam provision path and the drainage path; and a safety control circuit coupled to the one or more valves, wherein in the event of a loss of power to the safety control circuit, the one or more valves are arranged to adopt a default steam drainage configuration in which the passage of steam to the head unit via the steam provision path is blocked and steam is allowed to escape the steam generating apparatus via the drainage path. Viewed from a second aspect, there is provided a method of operating a steam generating apparatus for a receptacle cleaning device, the method comprising: heating water to generate steam; selectively supplying steam to a head unit of the receptacle cleaning device via a steam provision path and allowing the steam to escape the steam generating apparatus via a drainage path without passing through the head unit; and in the event of a loss of power to a safety control circuit of the steam generating apparatus, adopting a default steam drainage configuration by: blocking the passage of steam to the head unit via the steam provision path; and allowing steam to escape the steam generating apparatus via the drainage path. Viewed from a third aspect, there is provided a system comprising a cleaning fluid heating apparatus for a receptacle cleaning device, the cleaning fluid heating apparatus comprising: a heater to heat cleaning fluid; a cleaning fluid provision path for supplying cleaning fluid to a head unit of the receptacle cleaning device; a drainage path, separate from the cleaning fluid provision path, to allow cleaning fluid to escape the cleaning fluid heating apparatus without passing through the head unit; one or more valves arranged to control the flow of cleaning fluid along the cleaning fluid provision path and the drainage path; and a safety control circuit coupled to the one or more valves, wherein in the event of a loss of power to the safety control circuit, the one or more valves are arranged to adopt a default drainage configuration in which the passage of cleaning fluid to the head unit via the cleaning fluid provision path is blocked and cleaning fluid is allowed to escape the cleaning fluid heating apparatus via the drainage path. Viewed from a fourth aspect, there is provided a method of operating a cleaning fluid heating apparatus fora receptacle cleaning device, the method comprising: heating cleaning fluid; selectively supplying heated cleaning fluid to a head unit of the receptacle cleaning device via a cleaning fluid provision path and allowing the cleaning fluid to escape the cleaning fluid heating apparatus via a drainage path without passing through the head unit; and in the event of a loss of power to a safety control circuit of the cleaning fluid heating apparatus, adopting a default drainage configuration by: blocking the passage of cleaning fluid to the head unit via the cleaning fluid provision path; and allowing cleaning fluid to escape the cleaning fluid heating apparatus via the drainage path. Optional features of the first aspect are also optional features of the second, third, and fourth aspects. The present techniques are concerned with steam generation for a receptacle cleaning device. While a conventional dishwashing appliance or handwashing may be used to wash receptacles, to take advantage of the benefits of steam cleaning, as described above, a receptacle cleaning device may be provided that makes use of steam as a cleaning fluid. Such a receptacle cleaning device may therefore provide particularly effective cleaning, sanitise the receptacle without the need for additional chemical cleaning agents, make use of less water, benefit from reduced drying times and / or be able to wash the receptacle more quickly. This approach may be particularly useful in an office environment or in a coffee shop environment or in a tea shop environment. For example, store customers may hand over a dirtied receptacle to the store staff who can make use of the device of the receptacle cleaning device to remove easily and quickly any residues in the interior of the receptacle while they begin to prepare the beverage. This saves time as the staff member is no longer required to hand wash the receptacle in order to make it clean for serving the fresh beverage. In other examples, the receptacle cleaning device may be provided in an area of the office, coffee shop or tea shop environment accessible to customers, allowing the customer to make use of the receptacle cleaning apparatus to clean the receptacle themselves (before and / or after consuming the beverage). The techniques described herein address safety concerns that can be associated with the use of a steam generation apparatus of the form that could be used in such a receptacle cleaning device. In accordance with the techniques described herein, there is therefore provided a system with a steam generating apparatus for supplying steam to a head unit of a receptacle cleaning device, the head unit being a portion of the receptacle cleaning device accessed by a user in normal use. The steam generating apparatus has a heater to heat water in order to generate the steam to be supplied to the receptacle cleaning device for use in cleaning the receptacle. The heater may for example be a flow-through heater to heat water pumped through the steam generating apparatus from a connected water supply. The steam, as generated by the steam generating apparatus, will contain water vapour and may also contain an aerosol of liquid water droplets. In some examples, a wet steam, containing a significant amount of liquid water droplets, may be used to provide particularly effective cleaning compared to a dry steam with less liquid water content. Having been heated, the steam can progress down either a steam provision path or a drainage path. The steam provision path may be arranged to supply steam to the head unit of the receptacle cleaning device (or more generally to any device making use of the steam). The drainage path, separate from the steam provision path, provides a route for the steam to escape the steam generating apparatus without passing through the head unit. Thus, the drainage path provides a safe exit path for the steam away from a user. To control the flow of steam along the steam provision path and / or the drainage path, one or more valves are provided that are able to prevent or allow the flow of steam along the respective paths. To allow steam to flow to the receptacle cleaning device, the one or more valves may be set so as to allow the flow of steam along the steam provision path and to block the flow of steam along the drainage path. On the other hand, to evacuate steam from the system away from the user, the one or more valves may be set to block the flow of steam along the steam provision path and to permit the flow of steam along the drainage path. In accordance with the techniques described herein, there is also provided a safety control circuit (also referred to as a watchdog circuit) connected to the valves to provide a failsafe condition in the event of irregularities occurring within system. This safety control circuit may be separate from a primary control system of the steam generating apparatus and may be provided as a fall-back to ensure redundancy in the control systems of the steam generating apparatus. The safety control circuit and the one or more valves are arranged such that in the event of a loss of power to the safety control circuit, the valves adopt a default steam drainage configuration in which steam is safely evacuated from the apparatus without being passed to a location where it is likely to come into contact with a user. Thus, in the steam drainage configuration, the one or more valves block the passage of steam to the head unit via the steam provision path while allowing the steam to escape via the drainage path. Therefore, if for some reason, the safety control circuit loses power, a failsafe is established whereby the one or more valves are set to a safe default position in which steam is diverted away from a location at which it could be encountered by a user. The safety control circuit could lose power for a number of reasons including failure of components within the safety control circuit or in response to opening a lid of the device. Thus, by making use of this approach, the safety control circuit ensures that steam cannot be provided to the head unit when such a failure has occurred. Additionally, in the steam drainage configuration, which is adopted by default when the safety control circuit loses power, a closed system containing the steam is avoided since the drainage path is automatically left open. This reduces the likelihood of a pressurised system containing the steam inadvertently being created within the steam generating apparatus, reducing the potential danger of the apparatus. The one or more valves could have multiple different arrangements that allow the default steam drainage configuration to be adopted when power to the safety control circuit is lost. For example, a single valve may be provided that couples the output of the heater to both the steam provision path and the drainage path with operation of the valve able to select between the paths. This valve may be configured such that it has a default position to directing steam along the drainage path unless overridden by the safety control circuit (and a primary control system). In some examples however, the one or more valves include a normally-closed (NC) supply valve that is arranged on the steam provision path and a normally-open (NO) drain valve arranged on the drainage path. The NC supply valve defaults to a closed position in the absence of a current on the safety control circuit thereby preventing the flow of steam into the head unit in the event of loss of power to the safety control circuit. Conversely, the NO drain valve defaults to an open position in the absence of a current on the safety control circuit so as to allow the steam to escape the steam generating apparatus. Thus, by arranging both of these valves on the same circuit, it is possible to prevent a pressurised system inadvertently being created while ensuring a safe default behaviour in the event of a loss of power to the safety control circuit. The steam generating apparatus may be used as part of a receptacle cleaning system incorporating a head unit which is able to receive and wash the receptacle. In some examples, the head unit has a receiving component for receiving and holding the receptacle, a nozzle that is directed at the interior of the receptacle when the receptacle is held by the receiving component, and a lid for enclosing the receptacle in the receiving component. Thus, the head unit is capable of delivering a cleaning medium in the form of steam to an interior wall of the receptacle to clean the interior wall of the receptacle. In some examples, the receiving component comprises a first rotating element that is capable of rotating the receptacle. There is then provided a rotation driving component comprising a second rotating element, where the rotation driving component is arranged to drive rotation of the second rotating element. The second rotating element is magnetically coupled to the first rotating element such that rotation of the second rotating element by the rotation driving component drives rotation of the first rotating element. As mentioned above, the head unit in which the receptacle is placed for cleaning may have a lid to allow access to a receiving component of the device in which the steam is delivered during a cleaning cycle. In some examples, to detect opening of the lid and shut off the supply of steam to the head unit, the safety control circuit has a switch connected to the lid that is responsive to opening of the lid to cut power to the safety control circuit. By breaking the safety control circuit, the one or more valves will adopt the default steam drainage configuration and thus prevent steam being delivered to the head unit when the lid is open. This can help to prevent steam being delivered to an environment that the user may be operating in and in which the user could be susceptible to experiencing burns if the steam were not drained. The system may have a primary control system for controlling the operations of the steam generating apparatus and the head unit, with the safety control circuit providing redundancy in case of failure of the primary control system. The primary control system may have its own sensor (such as a Hall effect sensor) to detect the lid being opened, with the primary control system being responsive to opening of the lid to block the flow of steam to the head unit and to allow steam to escape the steam generating apparatus. In some examples, the primary control system also turns off the heater in response to detecting that the lid is opened in order to cease the generation of additional steam. Even with this functionality provided within the primary control system, the inventors recognised that there could still be times at which the primary control system or the sensor failed and did not adequately respond to the opening of the lid. To improve user safety therefore, in addition to the above-described functionality of the primary control system which may be implemented in software / firmware, the safety control circuit may provide a more reliable electromechanical failsafe in case of malfunction of the primary control system and / or the sensor. In some examples, the control system can be remotely operated and is responsive to a halt message received via a communication interface to cause the valves to adopt the drainage configuration in order to prevent further steam being provided to the head unit. This may for example allow staff in a coffee shop or conference environment to quickly shut-down the steam generating apparatus if they observe irregular behaviour of the receptacle cleaning device or inappropriate use of the device by a user. The communication interface could take a number of possible forms. For example, the communication interface may be a Bluetooth™ communication interface or a network interface card for communicating via a computer network. In further examples, other forms of suitable communication could be used such as personal area networks (e.g., Zigbee™, Wireless USB™, Wi-Fi™ or Near-Field Communication (NFC)) or wired communication using a physical connection technology such as USB™, a serial port, or FireWire™. It will be appreciated that the form of communication interface will be dependent on the communication technology used. As an additional layer of safety to further reduce the likelihood of steam being supplied to the head unit when it should not be or pressurised steam collecting within the steam generating apparatus, an alternating current (AC) power relay (or more generally a power relay) that couples (AC) power to the heater may be connected to the safety control circuit. Consequently, in the event of a loss of power to the safety control circuit (whether through malfunction or the lid being opened), the safety control circuit will cut power to the heater. The heater will therefore stop heating water to produce steam, preventing further heat being introduced to the system. Another way in which unintended supply of steam to the head unit may be prevented in case of malfunction of the primary control system is by requiring a varying control signal from the primary control system in order to control the one or more valves to block the drainage path and / or allow steam to pass along the steam provision path. For example, the valves may require a square wave signal to be provided by the primary control system in order to move from their default positions. Requiring this varying control signal may help to reduce the impact of stuck-at faults in the primary control system whereby a signal from the primary control system becomes stuck at a particular value. As a yet further mechanism to ensure safe handling of steam within the system, a mechanical pressure release valve may be provided within the steam generating apparatus that is responsive to steam pressure exceeding a threshold pressure to provide an additional path for steam to drain without passing through the head unit. In addition to or instead of the mechanical pressure release valve, one or more pressure sensing devices (such as a pressure switch of pressure sensor) may be provided to measure a pressure at points in the apparatus. Such pressure sensing devices may be coupled to the primary control system and / or the safety control circuit and configured such that in the event of a certain pressure threshold being exceeded, a drainage configuration is adopted (e.g., by opening the drain valve) to release the pressure within the apparatus. Such pressure sensing devices may be used as an initial layer of detecting pressure build-up (e.g., due to blockages within the apparatus) with the mechanical pressure release valve used as a further layer of redundancy. Although the present techniques have been discussed in relation to a steam generating apparatus, similar techniques may be used within other heating systems where cleaning fluid is heated to provide a heated cleaning fluid other than steam. In such cases, the cleaning fluid may be water which may be used in combination with a detergent. Brief Description of the Drawings Further aspects, features, and advantages of the present technique will be apparent from the following description of examples, which is to be read in conjunction with the accompanying drawings, in which: Figure 1 is a schematic illustrating a head unit of a receptacle cleaning device in accordance with an example; Figure 2 is a schematic illustrating a steam generating apparatus in a steam drainage configuration in accordance with an example; Figure 3 is a schematic illustrating the steam generating apparatus in a steam provision configuration in accordance with an example; Figure 4 schematically illustrates the steam generating apparatus of Figures 2 and 3 along with a number of further safety systems; Figure 5 schematically illustrates the steam generating apparatus of Figure 4 additionally incorporating pressure sensing devices and a communication interface; Figure 6 is a flowchart illustrating logical behaviour performed within the steam generating apparatus to prevent the production of steam while the lid of the receptacle cleaning device is open; Figure 7 schematically illustrates a receptacle cleaning device in which the present techniques may be implemented; Figure 8 shows a receptacle cleaning device in which the present techniques may be implemented; and Figures 9A-9B show a device for cleaning a receptacle in which the device is arranged as a split system. Detailed Description Before discussing the examples with reference to the accompanying figures, the following description of examples is provided. Figure 1 is a schematic illustrating a head unit 4 of a receptacle cleaning device in accordance with an example. The head unit 4 has a receiving component 6 that defines a chamber 12 in which a receptacle 10 to be washed can be placed. A lid 8 of the device can then be shut to enclose the receptacle 10 in the chamber 12. With the receptacle 8 enclosed in the chamber 12, a user may initiate a cleaning cycle of the receptacle cleaning device. During the cleaning cycle, the receptacle cleaning device uses steam (or more generally, cleaning fluid) to clean the receptacle 10. In this example, two cleaning jets 46, 48 are provided: a centre jet 46 with a nozzle directed at an interior of the receptacle 10 and an external jet 48 directed an exterior of the receptacle 10. This arrangement allows both the interior of the receptacle 10 and the exterior of the receptacle 10 to be cleaned; however, in other examples, different arrangements of jets may be used and more or fewer jets may be used. In some examples, a single jet directed at the interior of the receptacle 10 may be provided on the basis that the interior of the receptacle 10 is likely to be the region most in need of cleaning. In some examples, the receiving component 6 has a rotating element in which the receptacle 10 is placed to enable rotation of the receptacle 10 during cleaning so as to provide better cleaning coverage during the cleaning cycle. The jets 46, 48 are supplied with cleaning medium in the form of steam by steam inlets 44 that are fed by a steam generating apparatus. Spent cleaning medium can be drained from the head unit 4 via a waste port 52. To ensure that the steam supplied from the jets 46, 48 is confined within the head unit 4 and that users are not exposed to the steam, the cleaning cycle is carried out when the lid 8 is in a closed position. Control systems are provided to prevent steam being supplied to the chamber 12 while the lid 8 is open. To allow these control systems to determine when the lid has been opened, a sensor in the form of a Hall effect sensor 34 is provided as well as a micro switch 32. The operation of the Hall effect sensor 34 and the micro switch 32 will be discussed in more detail with reference to Figure 4. Figure 2 is a schematic illustrating a steam generating apparatus 14 in a steam drainage configuration in accordance with an example. The steam generating apparatus 14 receives water via a water inlet 54 which can be used to generate steam to be supplied to a device, such as the head unit 4 via steam outlets 42. Here, the steam outlets 42 together provide a steam provision path to the head unit 4. The steam generating apparatus 14 also has a steam outlet 50 that provides a drainage path for steam from the apparatus 14 without passing to the head unit 4. To generate steam, water from the water inlet 54 is pumped through the device by pump 62 and through a check valve 64 that prevents backflow of the water into the pump 62. The water is then heated by a flow through heater 66 to produce steam. The steam is then directed by valves 22, 24, 26 to pass either through the steam outlets 42 to the head unit 4 or along the drainage path 50. As shown in Figure 2, the steam generating apparatus 14 is in a steam drainage configuration in which the supply valves 22, 24 are in a closed position to prevent steam proceeding to the steam outlets 42 and the drain valve 26 is in an open position to allow steam to drain from the apparatus 14. The valves are arranged such that this steam drainage configuration represents a default configuration that is adopted in the absence of control signals causing a steam provision configuration (depicted in Figure 3) to be adopted. This default status is achieved here by providing normally-closed (NC) valves as the supply valves 22, 24 and a normally-open (NO) valve as the drain valve 26; however, it will be appreciated that other arrangements of valves and conduits within the apparatus 14 such that the default steam drainage configuration may be achieved using other types of valves. Figure 3 is a schematic illustrating the steam generating apparatus 14 in a steam provision configuration in accordance with an example. In Figure 3, the drain valve 26 is now in a closed position and the supply valves 22, 24 are in open positions. Thus, the steam generated by the heater 66 is allowed to pass through the steam outlets 42 into the head unit 4. This configuration may be employed during a cleaning cycle and may be adopted in response to control signals from a control system to override the default steam drainage configuration shown in Figure 2. As well as defaulting to the safer steam drainage configuration in which the steam is directed away from the head unit 4 where it is more likely to come into contact with a user, this arrangement of the steam generating apparatus helps to prevent accidentally forming a pressurised steam system. By providing NO supply valves and a NC drain valve, the supply valves and the drain valve will by default have different states to each other ensuring that regardless of the configuration of the steam generating apparatus 14, at least one path is provided to allow the steam to escape the apparatus 14. Figure 4 schematically illustrates the steam generating apparatus 14 of Figures 2 and 3 along with a number of further safety systems. As depicted in Figure 4, there is provided a safety control circuit 100 connecting the valves 22, 24, 26 in series with the lid micro switch 32 and an AC power relay 90. The safety control circuit 100 acts as a watchdog circuit to provide a failsafe in case of malfunction within a primary control system 102. By connecting the valves 22-26 in this way, if the safety control circuit 100 is unpowered, the supply valves 22, 24 will be closed and the drain valve 26 will be open, allowing steam in the apparatus 14 to drain via the drainage path 50. In the event of a loss of power to the safety control circuit 100, the valves 22, 24, 26 adopt the default steam drainage configuration. This loss of power could occur due to a malfunction in the safety control circuit or as a result of the lid 8 of the head unit 4 being opened as detected by the lid micro switch 32. The use of the lid micro switch 32 therefore ensures that steam is not provided to the head unit 4 when the lid 8 is opened, even if the primary control system 102 were otherwise (e.g., due to malfunction) to try to control the supply valves 22, 24 to open. The safety control circuit 100 is also provided with an AC power relay 90 that couples the power supply of the steam generating apparatus 14 to the heater 66 (and in some examples the pump 62). Consequently, when the safety control circuit 100 is unpowered, the power is also cut to the heater 66 to prevent more steam being generated. The safety control circuit 100 acts as a fall-back for the primary control system 102 which controls the operations of the system during normal operation. The primary control system 102 has a microcontroller 80 that is arranged to control the operation of the valves 22, 24, 26. The microcontroller 80 may be responsive to user input (e.g., via buttons on a user interface of the head unit 4) to start a cleaning cycle and hence allow steam to be produced and provided to the head unit 4. The microcontroller 80 is connected to the Hall effect sensor 34 that senses opening of the lid 8 and so the microcontroller 80 can be responsive to the lid 8 being opened to control the valves 22, 24, 26 to adopt the steam drainage configuration and turn off the flow through heater 66. In this sense, the primary control system 102 provides primary control of the apparatus 14 with the safety control circuit 100 acting as a safeguard. The supply valves 24, 26, the drain valve 26, and the heater 66 and pump 62 are responsive to a square wave signal that must be provided in order for the supply valves 24, 26 to open, the drain valve 26 to close, and the heater 66 and pump 62 to operate. The microcontroller 80 is connected to a square wave generator 82 that is able to generate this square wave that can be supplied to the valves 24, 26, 26, heater 66 and pump 62 as appropriate under the control of the microcontroller 80. Therefore, even if control signals are received from the microcontroller 80, if those control signals do not take the form of the required square wave, the components will not respond to the control signals, thereby reducing the likelihood of “sticky” signals from the microcontroller 80 leading to unexpected behaviour of these components. The steam generation apparatus 14 is also provided with a mechanical pressure release valve 70 arranged to allow steam or water to escape the steam generation apparatus 14 in the event that a pressure within the system exceeds a threshold. Although the mechanical pressure release valve 70 has been depicted in Figures 2-5 as providing a pressure release from the path between the check valve 64 and the flow through heater 66, it should be appreciated that a mechanical pressure release valve could additionally or alternatively be provided elsewhere within the apparatus 14. For example, a mechanical pressure release valve may be provided to detect and release excessive pressure occurring after the flow through heater 66. Figure 5 schematically illustrates the steam generating apparatus of Figure 4 while additionally incorporating a pressure switch 502, a pressure sensor 504 and in which the control system 102 has a communication interface 84. The pressure switch 502 and pressure sensor 504 provide additional mechanisms for detecting a build-up of pressure within the apparatus 14. As shown in Figure 5, a pressure sensor 504 is arranged before the heater 66 in the flow path through the apparatus 14. The pressure sensor 504 is in communication with the microcontroller 80 that implements the primary control system 102 such that the primary control system 102 can be responsive to the pressure sensor 504 detecting a pressure above a given threshold, to control the drain valve 26 to open, thereby allowing a release of pressure. The primary control system 102 may also deactivate the heater 66 and / or the pump 62 in response to detection of this high pressure condition. The threshold pressure at which the primary control system 102 is configured to respond may be set to a lower pressure than a pressure threshold at which the mechanical pressure release valve 70 opens such that the mechanical pressure release valve 70 functions as fall-back in case of failure with the primary control system 102. A pressure switch 502 is also provided, positioned on the steam path following the heater 66 and connected to the safety control circuit 100. The pressure switch 502 is configured such that if the steam pressure at the pressure switch 502 exceeds a certain threshold, the switch 502 is opened, thereby causing the default steam drainage configuration to be adopted. Thus, the pressure switch 502 and pressure sensor 504 provide additional pressure sensing devices that are able to reduce the likelihood of a pressurised system being formed within the steam generating apparatus 14. While the pressure switch 502 has been depicted as being located after the heater 66 and connected to the safety control circuit 100, and the pressure sensor 504 has been depicted before the heater 66 and connected to the primary control system 102, it should be appreciated that other implementations may be used in which different pressure sensing devices are used, the pressure sensing devices are located elsewhere in the apparatus 14 and / or are different connections to the primary control system 102 or safety control circuit 100 are made. As illustrated in Figure 5, the primary control system 102 has a communication interface 84 which may for example be a Bluetooth™ interface or a Wi-Fi™ interface. The communication interface 84 enables communication between the receptacle cleaning device and external devices and may be used monitor the status of, and / or collect usage information for, the receptacle cleaning device. This communication channel may also be used to allow the steam generating apparatus 14 to be remotely deactivated. For example, a deactivation signal may be sent by a remote device to the microcontroller 80 via the communication interface 84 whereupon the microcontroller 80 causes the drain valve 26 to be opened; the supply valves 22, 24 to be closed; the heater 66 to be deactivated; and / or the pump 62 to be deactivated. Figure 6 is a flowchart illustrating logical behaviour performed within the steam generating apparatus to prevent the production of steam while the lid 8 of the receptacle cleaning device is open. If the lid is open, as indicated at step 100, the micro switch 32 will be open as indicated in step 102, thereby removing power from the safety control circuit 100 (also referred to as the watchdog circuit) as indicated in step 104. In this example, the valves 22, 24, 26 are not directly connected to the safety control circuit 100 but rather a relay is connected to the safety control circuit 100 that couples power to the valves. Nonetheless, the safety control circuit 100 exhibits similar behaviour in the sense that loss of power to the watchdog circuit causes this relay to open as indicated in step 108, ensuring that the supply valves 22, 24 are closed and the drain valve 26 is opened, as depicted in step 112. Additionally, deactivation of the watchdog circuit 104 causes the AC relay 90 to be opened in step 106 ensuring that the heater 66 and the pump 62 are not powered, as indicated in step 110. As such, residual steam within the steam generating apparatus 14 is allowed to drain via the drainage path 50 and the AC components cannot be powered in order to generate more steam. On the other hand, if the lid is closed at step 100, the lid micro switch 32 will be closed at step 116, activating the watchdog circuit at step 118. Consequently the AC relay will be closed at step 120 and the 12V relay will be closed at step 112 powering the heater 66 and the pump 62 at step 124 and allowing the supply valves 22, 24 to be opened and the drain valve 26 to be closed. This corresponds to the normal operation of the device as indicated in step 128 in which a cleaning cycle may be carried out and steam supplied to the head unit 4. Figures 7-9B depict example systems in which the present techniques may be applied. Figure 7 schematically illustrates a receptacle cleaning device. Referring to Figure 7, there is provided a comprising a steam generating apparatus 14 that generates steam that is used to clean the interior of a receptacle (not shown in Figure 7). The steam generating apparatus 14 comprises a water source 610 operably connected to a hose 620 that is operably connected to a water pump 62. The water pump 62 is operably connected to a water heater 66 that is operably connected to a pressure sensor 650. The pressure sensor 650 is operably connected to a supply valve 23 that is operably connected to a head unit 4 of the device (not shown in Figure 7). Also referring to Figure 7, the steam generating apparatus 14 comprises an electronic control box 670 that acts as a primary control system and that is operably connected to each of the water pump 62, the water heater 66, the pressure sensor 650 and the supply valve 23- such as by means of electrical leads or cables (not shown in Figure 7). The device has generally two separate cycles in normal usage (i.e., when not interrupted by the safety control systems): namely a standby cycle and an operating cycle. In the case of the standby cycle: the supply valve 23 is closed, the pump 62 delivers water from the water source 610 through the water heater 66 and the pressure sensor 650. When a sufficient body of water is in the water heater 66 and the pressure sensor 650, the pump 62 turns off and encloses said body of water in the channel comprising the water heater 66 and pressure sensor 650. Upon the pump 62 turning off, the water heater 66 turns on. This action causes the body of water in said channel to vaporise and increase the pressure in the channel comprising the water heater 66 and the pressure sensor 650. The pressure sensor 650 relays the measured pressure value of said channel to the electronic control box 670. The electronic control box 670 receives this value and compares it against a preconfigured standby pressure value. If the pressure sensor 650 value exceeds the preconfigured standby pressure value, the electronic control box 670 signals to the water heater 66 to turn off. The pressure within said channel of water heater 66 and pressure sensor 650 will then fall. Once the pressure sensor 650 returns a value that does not exceed the preconfigured standby pressure value, the water heater 66 will turn on again. This cycle continues indefinitely until the steam generating apparatus 14 is either turned off or the user initiates the operating cycle. In the case of the operating cycle, the user (not shown) will place the beverage vessel 10 into a head unit 4 of the device. The user will then close the lid 8, enclosing the beverage vessel 10 within the device. Then the user will initiate the operating cycle by means of a human interface module. Upon this, the human interface module sends a signal to the electronic control box 670. The electronic control box 670 compares the current value of the pressure sensor 650 to the preconfigured operating pressure value. If the pressure sensor 650 value is lower than the preconfigured operating pressure value, the electronic control box 670 signals to the water heater 66 to turn on. Once the pressure sensor 650 value equals or exceeds the preconfigured operating pressure value, the control box 670 sends a signal simultaneously to the water pump 62 and the supply valve 23. The water pump 62 will turn on and the supply valve 23 will open. Water from the water source 610 will now be pumped constantly through the water heater 66 and vaporise to steam. This vaporised fluid continues through the now open supply valve 23 to head unit 4. The flow of vaporised fluid travels to the head unit 4 where it can be delivered into the head unit 4 via the jets at high speed. The flow of vaporised fluid proceeds to remove residue from the internal face of the beverage vessel 10. At the point the valve 23 is opened and the pump 62 is turned on, the electronic control box 670 may trigger rotation of a rotating component of the head unit 4 to allow the flow of vaporised fluid to remove residue from the complete circumference of the internal face of the beverage vessel 10. After a preconfigured duration, the electronic control box 670 sends a signal simultaneously to the pump 62, the water heater 66, and the supply valve 23. The pump 62 and the water heater 66 will now turn off and the supply valve 23 will close. Following this the flow of vaporised fluid from the steam generating apparatus 14 to the head unit 4 halts. Upon the halting of the flow of vaporised fluid, the user is now informed via the human user interface module to open the lid 8 and remove the cleaned beverage vessel 10. This marks the end of the operating cycle. Following the end of the operating cycle, the steam generating apparatus 14 will automatically return to the standby cycle until the next operating cycle is initiated or until the apparatus 14 is switched off. Figure 8 shows a receptacle cleaning device 2 in which the present techniques may be implemented. The receptacle cleaning device 2 comprises a receiving component for receiving and holding a receptacle 10 and a nozzle with a steam jet that is extendable into at least a part of the interior of the receptacle when the receptacle is placed on the receiving component. The device 200 comprises: a main body enclosure 230 which operably connects to a lid 210 and a human user interface module 220. The steam generating apparatus 14 and the receiving component 6 are both enclosed in the casing 230. Figures 9A-9B show a device for cleaning a receptacle in which the device is arranged as a split system with a head unit 4 including the components that the user interacts with and an auxiliary unit (which may be an under counter unit) containing at least a cleaning medium provision apparatus (e.g., a steam generating apparatus 14). By arranging the device as a split system in this way, the head unit 4 can be situated separately from the auxiliary unit providing flexibility as to the arrangement of the device, especially where space for the device is constrained. As shown in Figure 9A, the head unit 4 may be arranged within a surface 990 of a cabinet 995 with the auxiliary unit positioned within the cabinet 995 such that the auxiliary unit is hidden from view when a front panel or door (not shown) of the cabinet 995 in in place. As shown, the head unit 4 and the auxiliary unit are connected via conduits 1015. These conduits 1015 may comprise a power and interface cable, one or more steam outlets for the provision of steam (or other cleaning medium) to the head unit 4 and the return of excess steam to the auxiliary unit. Additionally a waste path may be provided from the head unit 4 which may be directed via the auxiliary unit or may be expelled directly to waste. The auxiliary unit may be provided with a water supply and power supply and has a connection to expel steam or condensed water (e.g., as an emergency release). Thus there has been described a system and method for washing receptacles such as coffee cups that is able to make use of hot cleaning fluids such as steam while providing safeguards to prevent the unintended creation of a pressurised steam system or the accidental release of steam into areas of the system being used by users. The present techniques can be considered to provide at least six separate layers of steam safety mechanism: • Layer 1: a safety control circuit coupled to one or more valves that provide a default steam drainage configuration in the event of loss of power to the safety control circuit; • Layer 2: an electromechanical response to the lid being opened in the form of a switch that ensures that the default steam drainage configuration is adopted when the lid is open; • Layer 3: the switch in the lid cutting power to the heater and / or pump when the lid is opened to prevent the generation of more steam; • Layer 4: a sensor incorporated within a primary control system to detect the lid being opened and drain the steam when opening of the lid is detected; • Layer 5: the valves, pump and / or heat requiring a varying control signal in order to be controlled so as to reduce the likelihood of stuck-at faults in the control system causing unexpected behaviour; • Layer 6: a pressure sensing device to detect an excessive pressure occurring within the system and to trigger a drainage configuration to be adopted to allow the steam to escape; • Layer 7: a mechanical pressure release valve to release steam from the system if a threshold pressure is exceeded; and • Layer 8: a remote deactivation option for the steam generating apparatus. In accordance with the techniques described herein, each of these layers may be implemented separately or in combination with any one or more other layers as part of a steam safety system. In the present application, the words “configured to...” are used to mean that an element of an apparatus has a configuration able to carry out the defined operation. In this context, a “configuration” means an arrangement or manner of interconnection of hardware or software. For example, the apparatus may have dedicated hardware which provides the defined operation, or a processor or other processing device may be programmed to perform the function. “Configured to” does not imply that the apparatus element needs to be changed in any way in order to provide the defined operation. Although illustrative examples of the invention have been described in detail herein 5 with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise examples, and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope and spirit of the invention as defined by the appended claims. 10

Claims

1. A system comprising a steam generating apparatus for a receptacle cleaning device, the steam generating apparatus comprising:a heater to heat water to generate steam;a steam provision path for supplying steam to a head unit of the receptacle cleaning device;a drainage path, separate from the steam provision path, to allow steam to escape the steam generating apparatus without passing through the head unit;one or more valves arranged to control the flow of steam along the steam provision path and the drainage path; anda safety control circuit coupled to the one or more valves, wherein in the event of a loss of power to the safety control circuit, the one or more valves are arranged to adopt a default steam drainage configuration in which the passage of steam to the head unit via the steam provision path is blocked and steam is allowed to escape the steam generating apparatus via the drainage path.

2. The system according to claim 1, wherein:the one or more valves comprise at least one normally-closed (NC) supply valve arranged on the steam provision path and at least one normally-open (NO) drain valve arranged on the drainage path; andin the event of a loss of power to the safety control the circuitry, the at least one NC supply valve is arranged to block the passage of steam to the head unit via the steam provision path and the at least one NO drain valve is arranged to allow steam to escape the steam generating apparatus via the drainage path to adopt the default steam drainage configuration.

3. The system according to claim 1 or claim 2, wherein the system further comprises the head unit, the head unit comprising:a receiving component for receiving and holding the receptacle;a nozzle arranged to be directed at an interior of the receptacle when the receptacle is held by the receiving component; anda lid for enclosing the receptacle in the receiving component.

4. The system according to claim 3, wherein the safety control circuit comprises a switch connected to the lid, wherein the switch is responsive to opening of the lid to cut power to the safety control circuit.

5. The system according to any preceding claim, the system further comprising a control system for controlling the operations of the steam generating apparatus, wherein the safety control circuit provides redundancy in the case of failure of the control system.

6. The system according to any preceding claim, wherein the safety control circuit is responsive to loss of power in the safety control circuit to cut power to the heater.

7. The system according to any preceding claim, wherein:the safety control circuit comprises an alternating current (AC) power relay to couple an AC power supply to the heater; andthe AC power relay is responsive to loss of power from the safety control circuit to disconnect the AC power supply to the heater unit8. The system according to claim 3 or any claim dependent thereon, wherein:the system comprises a control system for controlling the operations of the steam generating apparatus and a sensor to detect opening of the lid; andthe control system is responsive to opening of the lid as detected by the sensor to control the one or more valves to block the passage of steam to the head unit via the steam provision path and to allow steam to escape the steam generating apparatus via the drainage path.

9. The system according to claim 8, wherein the control unit is additionally responsive to opening of the lid to turn off the heater.

10. The system according to claim 8 or claim 9, wherein to control the one or more valves to allow steam to pass to the head unit via the steam provision path and / or to block the passage of steam via drainage path, the control unit is configured to send a varying control signal to the one or more valves.

11. The system according to claim 10, wherein the varying control signal is a square wave.

12. The system according to any of claims 8-11, wherein the sensor is a Hall effect sensor.

13. The system according to any of claims 8-12, wherein the control system comprises a microcontroller.

14. The system according to any preceding claim, further comprising a pressure sensing device coupled to at least one of the safety control circuit and a control system, wherein the at least one of the safety control circuit and the control system are responsive to detecting a pressure at the pressure sensing device that exceeds a threshold to provide a drainage path from the steam generating apparatus without passing through the head unit15. The system according to any preceding claim, further comprising a mechanical pressure release valve responsive to detecting a pressure at the mechanical pressure release valve exceeding a threshold to provide a drainage path from the steam generating apparatus without passing through the head unit.

16. The system according to claim 5 or any claim dependent thereon, wherein:the control system comprises a communication interface for receiving external instructions; andthe control system is responsive to a remote halt message received over the communication interface to control the one or more valves to block the passage of steam to the head unit via the steam provision path and to allow steam to escape the steam generating apparatus via the drainage path and / or to deactivate at least one of the heater and a pump.

17. A method of operating a steam generating apparatus for a receptacle cleaning device, the method comprising:heating water to generate steam;selectively supplying steam to a head unit of the receptacle cleaning device via a steam provision path and allowing the steam to escape the steam generating apparatus via a drainage path without passing through the head unit; andin the event of a loss of power to a safety control circuit of the steam generating apparatus, adopting a default steam drainage configuration by:blocking the passage of steam to the head unit via the steam provision path; andallowing steam to escape the steam generating apparatus via the drainage path.

18. A system comprising a cleaning fluid heating apparatus for a receptacle cleaning device, the cleaning fluid heating apparatus comprising:a heater to heat cleaning fluid;a cleaning fluid provision path for supplying cleaning fluid to a head unit of the receptacle cleaning device;a drainage path, separate from the cleaning fluid provision path, to allow cleaning fluid to escape the cleaning fluid heating apparatus without passing through the head unit;one or more valves arranged to control the flow of cleaning fluid along the cleaning fluid provision path and the drainage path; anda safety control circuit coupled to the one or more valves, wherein in the event of a loss of power to the safety control circuit, the one or more valves are arranged to adopt a default drainage configuration in which the passage of cleaning fluid to the head unit via the cleaning fluid provision path is blocked and cleaning fluid is allowed to escape the cleaning fluid heating apparatus via the drainage path.

19. A method of operating a cleaning fluid heating apparatus for a receptacle cleaning device, the method comprising:heating cleaning fluid;selectively supplying heated cleaning fluid to a head unit of the receptacle cleaning device via a cleaning fluid provision path and allowing the cleaning fluid to escape the cleaning fluid heating apparatus via a drainage path without passing through the head unit; andin the event of a loss of power to a safety control circuit of the cleaning fluid heating apparatus, adopting a default drainage configuration by:blocking the passage of cleaning fluid to the head unit via the cleaning fluid provision path; andallowing cleaning fluid to escape the cleaning fluid heating apparatus via the drainage path.23

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