GB2640418A - Method of condition monitoring of a component in a circuit - Google Patents

Abstract

A method is provided for condition monitoring of a component in a circuit, comprising the steps of: i) determining a voltage drop across the component; ii) integrating the voltage drop over a given period of time to calculate an energy metric representative of the energy dissipated by the resistance of the component over the period of time; iii) comparing the energy metric to a predetermined threshold energy metric; and iv) if the energy metric is greater than the predetermined threshold energy metric, deeming that the component has overheated. The method can be applied to a battery charger in a battery charge station, for example in a cubic storage and retrieval system.

Description

Method of condition monitoring of a component in a circuit

Technical Field

The present disclosure relates to a method of condition monitoring of a component in a circuit, in particular to condition monitoring of a contactor in a charger for a rechargeable power source.

Background

Faults in electrical components can cause thermal overload. For example, wear and tear or other mechanical faults can cause the resistance of the component to increase. A current passing through the component will therefore cause energy to be lost through heat. As well as reducing efficiency, the resultant heat can contribute to the mechanical fault and cause a further increase in resistance, which in turn causes further heating, resulting in thermal runaway and eventual damage to the component. In the worst case scenario, the damage can render the component inoperative or even unsafe.

Overheating due to wear and tear or mechanical faults is a particular problem for electrical contactors. A contactor is an electrically controlled heavy-duty relay with a high current rating, designed for repeatedly opening and closing a circuit. The contactor comprises a coil, which generates a magnetic field when a current is passed through it. This magnetic field causes the contacts to close, in order to complete a circuit and allow power to flow. Contactors tend to be used for higher current-carrying applications than standard relays, since contactors are able to allow low voltages and currents to switch a far higher voltage/current circuit on and off. The higher currents and the repeated switching cycles means that contactors are particularly susceptible to mechanical damage and overheating.

Overload relays are one means of protecting a circuit from overheating. In electric motors, one of the main causes of failure is electrical overload (overcurrent), where a motor draws a current above its rated current for a prolonged period of time. To protect the motor windings and circuit, overload relays can be used. The most common kind of overload relay is a thermal overload relay, which uses a bi-metallic strip, comprising two different metals. The two metals of the bi-metallic strip have different coefficients of thermal expansion so expand at different rates when heated, which causes the bi-metallic strip to bend, open the relay, and break the circuit. Another option is electronic relays, which measure the current electronically, for example with a temperature sensor or current transformer or Hall effect sensor.

However, thermal overload relays are not suitable for electrical contactors. The bi-metallic strip of a thermal overload relay can take several seconds to activate, commonly 10 or 20 seconds, since enough thermal energy needs to be absorbed to bend the strip.

One method of protecting electric motors from high temperatures is known as "i2t", i.e. the square of electrical current integrated over a period of time. 12t is a measure of thermal energy resulting from current flow. Electrical power is voitage x current, and voltage is resistance x current, so electrical power is proportional to current squared in circuits with a constant voitage. Integrating electrical power over time t gives a measure of electrical energy. Assuming that a constant proportion of the electrical energy is converted to thermal energy (i.e. the component has a constant efficiency), thermal energy is proportional to current squared x time, hence the name i2t.

This method of estimating thermal energy is appropriate for components such as electric motor windings, which can be assumed to have a constant voltage, constant resistance, and variable current through the component. The i2t method, however, does require measurements of the current flowing through the component of interest. In a circuit that is not already set up for taking, current measurements, additional components will be needed to take and record these measurements, leading to increased cost and complexity.

Condition monitoring of electrical components is therefore needed, particularly for components that experience high electric currents such as electrical contactors. This disclosure presents an alternative method, which utilises components already in the circuit to provide a more direct measurement of the energy going into the component.

Summary

A method for condition monitoring of a component in a circuit is provided, the method comprising the steps of: i) determining a voltage drop across the component; ii) integrating the voltage drop over a given period of time to calculate an energy metric representative of the energy dissipated by the resistance of the component over the period of time; iii) comparing the energy metric to a predetermined threshold energy metric; and iv) if the energy metric is greater than the predetermined threshold energy metric, deeming that the component has overheated.

The energy metric is representative of the energy dissipated by the component over the period of time, but is not necessarily an actual energy value.

Step i) may comprise measuring the voltage drop across the component directly. Step i) may comprise measuring the voltage either side of the component, and calculating the voltage drop based on the difference. For example, a first voltage may be measured at one side of the component, and a second voltage may be measured at the other side of the component. The voltage drop may be calculated by subtracting the first voltage from the second voltage.

The method may further comprise the step of: v) if the component is deemed to have overheated, switching off the power supply to the component. The method may further comprise the step of: vi) if the component is deemed to have overheated, indicating that an error has occurred. Other appropriate actions may also be taken in response to the component being deemed to have overheated.

The predetermined threshold energy metric may be calculated based on an expected energy metric representative of the cumulative energy dissipated by the nominal resistance of the component over the period of time.

The expected energy metric may be calculated by: i) determining a nominal voltage drop across the component; and ii) integrating the nominal voltage drop over the given period of time.

The nominal voltage may be very small (for example, in the order of my). In some examples, the ideal nominal voltage of the component may be zero, but in practise the nominal voltage is a very small but non-zero voltage.

Step i) may comprise multiplying the nominal resistance of the component by the nominal current to calculate a nominal voltage drop across the component. Alternatively or additionally, the nominal voltage drop across the component can be measured directly, or calculated by measuring the voltage either side of the component and subtracting one from the other.

The predetermined threshold energy metric is calculated by multiplying the expected energy metric by a factor. The factor may be in the range 3 -10. The factor may depend on the component, i.e. a given component or type of component will always have the same factor, but different components may have different factors.

The predetermined threshold energy metric may be calculated based on a permitted temperature increase of the component. The predetermined threshold energy metric may be calculated by multiplying the permitted temperature increase of the component by the heat capacity of the component.

For example, a larger component or a component with a larger surface area may be more easily able to dissipate heat, so may have a larger factor. In cases where the component is a contactor, a larger contactor may have a lower expected resistance so could have a lower factor. Many different attributes such as the size, shape, rating, type, and specification of the component may affect the factor. In some cases the factor can be determined empirically.

A computer program is provided comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method described herein.

A charger is provided for charging a rechargeable power source, comprising: a circuit comprising a power supply and a contactor for switching power to the rechargeable power source; and a controller configured to carry out the method described herein. The controller may comprise a logic circuit or a computer program.

Advantageously, the controller is continually monitoring the contactor of the charger during a charging operation, so a fault will be detected very quickly. The rechargeable power source may be a rechargeable battery. The charger may be configured to charge the rechargeable power source in constant current mode.

A charge station is provided for charging a rechargeable power source in a load handling device, the charge station comprising: one or more chargers as described herein; and one or more charging bays configured to removably receive the rechargeable power source, each of the one or more charging bays being configured to electrically couple the rechargeable power source to a respective charger.

The charge station may further comprise a transfer mechanism configured to move the rechargeable power source between the load handling device and the charging bays.

A storage and retrieval system is provided, comprising: a) a grid framework structure comprising: i) a track system comprising a plurality of tracks arranged in a grid pattern; ii) a supporting framework structure supporting the track system; and iii) a plurality of stacks of storage containers arranged in stacks a plurality of storage columns located below the track system; b) one or more load handling devices for lifting and moving the storage containers, each load handling device comprising: i) a driving assembly configured to move the load handling device on the track system; ii) an exchangeable rechargeable power source configured to power the driving assembly; iii) a container-holding assembly configured to releasably hold a storage container from above; and iv) a lifting mechanism configured to raise and lower the a container-holding assembly; c) one or more charge stations as described herein.

Brief Description of Figures

Figure 1 illustrates a method of calculating an energy metric representative of the energy dissipated by the resistance of a component over the period of time: (a) voltage measurement (b) area under the curve (c) representative energy metric (d) expected energy metric.

Figure 2 is a schematic flow diagram illustrating the steps of a condition monitoring method. Figure 3 is a circuit diagram illustrating a contactor in a battery charger circuit.

Figure 4 is a schematic perspective view of a storage and retrieval system with grid framework structure, containers, and load handling devices.

Figure 5 is a schematic perspective view of a load handling device with a container-holding device in a position below the bottom of the load handling device.

Figure 6 is a schematic view of the load handling device with a battery received in a battery compartment, in (a) perspective view, and (b) cross-section view.

Figure 7 is a schematic illustration of a battery charge station, in (a) perspective view, and (b) top view. Figure 8 is a schematic illustration of a battery with battery electrical connector.

Figure 9 is a schematic view of the battery electrical connector, in (a) perspective view, (b) side view, and (c) top view.

Figure 10 is a schematic illustration of a battery charging bay with charging connector.

Figure 11 is a schematic view of the charging bay electrical connector, in (a) perspective view, (b) side view, and (c) top view.

Figure 12 is a schematic view of a charger rack of the battery charger station with contactors. Figure 13 is a more detailed view of the contactors in Figure 12.

Detailed Description

Method of calculating representative energy metric Figure 1 illustrates a method of calculating an energy metric representative of the energy dissipated by the resistance of a component over the period of time. In Figure 1(a), the voltage drop across a component is measured and plotted as a function of time. The dashed horizontal line represents the nominal or usual operational voltage of the component.

In this example the component has developed a mechanical fault, which increases its resistance. The increased resistance leads to an increased voltage drop across the component. It can be seen from Figure 1(a) that the measured voltage across the component begins at the nominal voltage and increases over time, initially only by a little, but then more significantly.

The heat generated by the component is related to the electrical energy applied. The component loses energy through its resistance, and the electrical energy lost is dissipated as heat. The power dissipated from the component is the product of its voltage drop and the current flowing through the circuit. The current is assumed to be constant, so integrating or summing the voltage drop over a period of time gives a measure of the energy dissipated as heat.

Figure 1(b) illustrates summing the voltage over a period of time. As power is proportional to voltage drop, a representation of the energy applied can be calculated by regularly sampling the voltage drop and summing the samples. The voltage is measured at a sampling rate (represented by the regularly spaced vertical lines representing the sampling times at regular intervals). The area under the curve is calculated by summing the areas between every two consecutive sampling times.

The total area under the curve is a representative energy metric, illustrated in Figure 1(c). This value is a measure of the energy dissipated by the resistance of the component over the period of time.

The representative energy metric can be compared against a predetermined threshold energy metric to determine whether too much energy has been dissipated. Excessive energy dissipation can lead to the temperature of the component rising and causing a further increase in resistance and potentially damaging the component. If the representative energy metric is greater than the predetermined threshold energy metric, the component is deemed to have overheated. Appropriate actions can then be taken, for example turning off the power supply and/or indicating that an error has occurred.

One method of determining a predetermined threshold energy metric is to first calculate an expected energy metric or nominal representative energy metric, i.e. the representative energy metric that would have resulted from the energy dissipated by the component at its nominal voltage over the same period of time. The area under the nominal voltage line as illustrated in Figure 1(d) is the expected energy metric, a measure of the cumulative energy dissipated by the nominal resistance of the component over the same period of time. The nominal voltage can be measured, or can be calculated from a known nominal resistance of the component and the current passing through it.

The predetermined threshold energy metric can be defined as a multiple of the expected energy metric. For example, the predetermined threshold energy metric can be defined as five times the expected energy metric. If the representative energy metric exceeds this threshold (in this example, if the representative energy metric is more than five times the expected energy metric), the component is deemed to have overheated. In this example, the component has dissipated five times the thermal energy over the given period of time that would be expected if the component's resistance had remained at its nominal value. A different multiple can be used, for example two or three or ten times the expected energy metric.

An example of the calculation method is provided below for a battery charger with a contactor. A battery is charged for 12 minutes at a current of 30 amps. The contactor has a contact resistance of 1.7 mO. The predetermined threshold energy metric is defined as four times the expected energy metric.

Voltage drop across contactor (V) = resistance (0) x current (A) Voltage drop across contactor = 1.7 mfg x 30A = 51 mV Power (W) dissipated by the contactor while charging = voltage across the contactor (V) * current (A) Power (W) dissipated by the contactor while charging = 51 mV x 30A = 1.53 W Expected energy metric (J) = power (W) * time (seconds) Expected energy metric (J) = 1.53 W * 12 * 60 = 1101.6 J Predetermined threshold energy metric = 4 x expected energy metric Predetermined threshold energy metric = 4 x 1101.6 J = 4406.4 J In this example the contactor will be considered to have overheated if the representative energy metric exceeds 4406.4 J. The representative energy metric here is an actual energy value measured in Joules.

In another example, the voltage drop across a new contactor for a battery charger is measured as 60 my, so 60 mV is taken as the nominal voltage. A battery is charged for 10 minutes. The predetermined threshold energy metric is defined as six times the expected energy metric.

Nominal voltage drop across contactor (V) = 60 mV Expected energy metric (Vs) = nominal voltage across contactor (W) * time (seconds) Expected energy metric (Vs) = 60 mV x 60 * 10 s = 36 Vs Predetermined threshold energy metric = 6 x expected energy metric Predetermined threshold energy metric (Vs) = 6 x 36 Vs = 216 Vs In the above example the contactor will be considered to have overheated if the representative energy metric exceeds 216 Vs. The representative energy metric here is measured in Vs, so is not an actual energy value (which would be measured in J), as in the previous example.

Another method of determining a predetermined threshold energy metric is to first calculate a permitted temperature increase, i.e. a temperature above which the component will be deemed to have overheated. The mass and specific heat capacity can be assumed to be constant for a given component. The predetermined threshold energy metric can therefore be calculated from the mass and specific heat capacity.

Predetermined threshold energy metric (J) = temperature delta (°C) x mass (kg) x specific heat capacity (J kg-1 °C1) Figure 2 is a flowchart illustrating an example of a method of condition monitoring a component in a circuit. In a step 101, the voltage drop across the component is measured. In a step 102, a representative energy metric is calculated. This value is a measure of the energy dissipated by the resistance of the component over a given period of time. In a step 103, the representative energy metric is compared to a threshold, for example the predetermined threshold energy metric as discussed above. If the representative energy metric is not above the threshold, monitoring continues (see arrow labelled "no" looping back to step 101). If the representative energy metric is above the threshold, in a step 104 the component is deemed to have overheated. As a result, actions can be taken to mitigate the effects. For example, in a step 105 the power supply to the component can be switched off, and/or in a step 106, there may be an indication that an error has occurred (for example, an error message or a visual indicator or an alarm).

In examples where voltage measurements are sampled regularly, the comparison in step 103 can be carried out at every sampling timestep. The representative energy metric can be calculated at each timestep for the time elapsed during the period from the time at which charging started to the time at which that sample voltage was measured. Similarly, the predetermined threshold energy metric will be calculated over the time period between the time at which charging started and the time at which that sample voltage was measured. The arrow labelled "no" from step 103 looping back to step 101 represents the repetition of this process at every timestep. In other examples, the sampling rate for summing the representative energy metric may be different from the rate at which the comparison in step 103 is carried out.

Application to a battery charger Figure 3 is a circuit diagram for a battery charger. The voltmeter symbols in solid circles represent places in the circuit where direct measurements of voltage can be taken, and the voltmeter symbols in dotted circles represent the places in the circuit where the voltage can be derived from other voltage measurements. In this battery charger there is a pair of contactors, one contactor on the charger side and another contactor on the battery side. The two switches K1 and K2 in Figure 3 represent the contactors on the charger and on the battery respectively, i.e. K1 is the charger side contactor and K2 is the battery side contactor.

The charger voltage Vchargen the battery voltage Vbatm,y, and the voltage Vmid at the point where the battery contactor touches the charger side contactor (i.e. the charger output voltage) are all measured directly. These voltages can be used to determine the voltage drop VI_ across the charger side contactor, and the voltage drop V2 across the battery side contactor: Vl = Vcharger Vmid V2 = Vmid VbaLtery Deriving the voltage drop across the contactors using this method rather than measuring directly is advantageous, because direct measurement needs specialized electronics. The common-mode voltages (Vcbarger -Verna)/2 and (Vmid -Vbattery)/2 are relatively large compared to the voltages to be measured Vi and V2, so a direct measurement of Vi and V2 would require some means of eliminating the common-mode voltages, e.g. a differential amplifier. Deriving the voltage drop from the difference between the voltages either side of the component is easier and does not require any additional instrumentation to be added to the circuit.

During a charging operation, the charger voltage Vtharge" the charger output voltage Vmid, and the battery voltage Vbattery are measured at a given sampling rate. The contactor voltage drop and the representative energy sum for the charger contactor and/or the battery contactor can be calculated from these voltage measurements, as described in more detail above. If the representative energy sum exceeds the predetermined threshold energy metric, the contactor is deemed to have overheated, so charging should be stopped. The method can be applied to the charger side contactor, the battery side contactor, or both.

Appropriate mitigation actions can be taken once the contactor is deemed to have overheated. Firstly, the power supply must be turned off. Both the charger side contactor and the battery side contactor can be de-energised, thus disconnecting the battery from the charger. The charger system can indicate that an error has occurred. Information about the error can be sent to a control system, which can then take appropriate actions. The error indication can take any suitable form, for example an error message displayed on a screen, or a visual indicator such as an LED, or an auditory signal such as an alarm. In some examples information about the error can be sent wirelessly to a mobile device, so that a worker remote from the charger will be alerted to the problem. The charger can be taken out of operation, i.e. no further charging will take place until the charger has been inspected and any required maintenance performed.

In some examples, more than one predetermined threshold energy metric can be defined, with a different error indication and/or set of mitigation actions for each. For example, if the representative energy sum exceeds a lower predetermined threshold energy metric, the charger could pause charging for a period of time to allow the components to cool down, and if the representative energy sum exceeds an upper predetermined threshold energy metric, the charger could stop charging immediately and send an error indication requesting attention from a technician or engineer.

Although the example circuit described above is for a battery charger, the same method can be used in other high-power applications.

Storage and retrieval system Cubic storage and retrieval systems are well known. For example, W02015185628 describes a storage and retrieval system in which stacks of storage containers are arranged within a grid framework structure. The storage containers are accessed from above by load handling devices operative on rails or tracks located on the top of the grid framework structure.

Figure 4 illustrates a storage structure 1 of a storage and retrieval system. The storage structure 1 comprises a grid framework structure comprising upright members 3 and horizontal members 5, 7 which are supported by the upright members 3. The horizontal members 5 extend parallel to one another and the illustrated x-axis. The horizontal members 7 extend parallel to one another and the illustrated y-axis, and transversely to the horizontal members 5. The upright members 3 extend parallel to one another and the illustrated z-axis, and transversely to the horizontal members 5, 7. The horizontal members 5, 7 form a grid pattern defining a plurality of grid cells 14. In the illustrated example, storage containers 9 are arranged in stacks 11 beneath the grid cells 14 defined by the grid pattern, one stack 11 of containers 9 per grid cell 14. In other examples, rather than upright members 3, the horizontal members can be supported by other kinds of supporting framework structure.

Load handling devices 25 (also known as bots 25) operate on a track system 13 on top of the grid framework structure. The track structure 13 may be provided by the horizontal members 5, 7 themselves (e.g. formed in or on the surfaces of the horizontal members 5, 7) or by one or more additional components mounted on top of the horizontal members 5, 7. The illustrated track system 13 comprises x-direction tracks 17 and y-direction tracks 19, i.e. a first set of tracks 17 which extend in the x-direction and a second set of tracks 19 which extend in the y-direction, transverse to the tracks 17 in the first set of tracks 17. The tracks 17, 19 define apertures at the centres of the grid cells 14.

The apertures are sized to allow containers 9 located beneath the grid cells 14 to be lifted and lowered through the apertures.

Figure 4 shows a plurality of load handling devices 25 moving on top of the storage structure 1. The load handling devices 25 are provided with sets of wheels to engage with corresponding x-or y-direction tracks 17, 19 to enable the load handling devices 25 to travel across the track structure 13 and reach specific grid cells 14. The tracks 17, 19 may be pairs of tracks to allow load handling devices to occupy (or pass one another on) neighbouring grid cells 14 without colliding with one another.

As illustrated in Figure 5, a bot 25 comprises an external body 27 in or on which are mounted one or more components which enable the bot 25 to perform its intended functions. These functions may include moving across the storage structure 1 on the track structure 13 and raising or lowering storage containers 9 (e.g. from or to stacks 11) so that the bot 25 can retrieve or deposit storage containers 9 in specific locations defined by the grid pattern.

The illustrated bot 25 comprises a driving assembly comprising first and second sets of wheels 29, 31 which are mounted on the external body 27 of the bot 25 and enable the bot 25 to move in the x-and y-directions along the tracks 17 and 19, respectively. In particular, two wheels 29 are provided on the shorter side of the bot 25 visible in Figure 5, and a further two wheels 29 are provided on the opposite shorter side of the bot 25. The wheels 29 engage with tracks 17 and are rotatably mounted on the external body 27 of the bot 25 to allow the bot 25 to move along the tracks 17. Analogously, two wheels 31 are provided on the longer side of the bot 25 visible in Figure 5, and a further two wheels 31 are provided on the opposite longer side of the bot 25. The wheels 31 engage with tracks 19 and are rotatably mounted on the external body 27 of the bot 25 to allow the bot 25 to move along the tracks 19.

To enable the bot 25 to move on the different wheels 29, 31 in the first and second directions, the driving assembly further comprises a wheel-positioning mechanism (not shown) for selectively engaging either the first set of wheels 29 with the first set of tracks 17 or the second set of wheels 31 with the second set of tracks 19. The wheel-positioning mechanism is configured to raise and lower the first set of wheels 29 and/or the second set of wheels 31 relative to the external body 27, thereby enabling the load handling device 25 to selectively move in either the first direction or the second direction across the tracks 17, 19 of the storage structure 1.

The bot 25 also comprises a lifting assembly 33 and a container-holding assembly 37 configured to raise and lower storage containers 9. The illustrated lifting assembly 33 comprises four tethers 35 which are connected at their lower ends to the container-holding assembly 37. The tethers 35 may be in the form of cables, ropes, tapes, or any other form of tether with the necessary physical properties to lift the storage containers 9. The container-holding assembly 37 comprises a gripping mechanism 39 configured to engage with features of the storage containers 9 to releasably hold the containers 9 from above. In the illustrated example, the gripping mechanism 39 comprises legs that can be received in corresponding apertures 10 in the rim of the storage container 9 and then moved outwards to engage with the underside of the rim of the storage container 9. The tethers 35 can be wound up or down to raise or lower the container-holding assembly 37 as required. One or more motors and winches or other means may be provided to effect or control the winding up or down of the tethers 35.

The bot 25 is externally open at the bottom and defines a container-receiving space for accommodating at least part of a storage container 9 that has been raised into the container-receiving space 45 by the lifting assembly 33. The container-receiving space is sized such that enough of a storage container 9 can fit inside the space to enable the bot 25 to move across the track structure 13 on top of storage structure 1 without the underside of the storage container 9 catching on the track structure 13 or another part of the storage structure 1. When the bot 25 has reached its intended destination, the lifting assembly 33 controls the tethers 35 to lower the container-holding assembly 37 and the corresponding storage container 9 out of the space 45 and into the intended position. The intended position may be a stack 11 of storage containers 9 or an egress point of the storage structure 1 (or an ingress point of the storage structure 1 if the bot 25 has moved to collect a storage container 9 for storage in the storage structure 1). The upper and lower configuration of the bot 25 allows the bot 25 to occupy only a single grid cell 14 on the track structure 13 of the storage system 1. In an alternative example, the container-receiving space may instead be adjacent to the external body 27 of the bot 25, e.g. in a cantilever arrangement with the weight of the external body 27 of the bot 25 counterbalancing the weight of the container 9 to be lifted.

Each load handling device is operated by a rechargeable power source. The rechargeable power source may be charged in situ by driving a load handling device to a charging station located at the edge of the track structure. The load handling device remains stationary at the charging station while the battery is recharged. The charging period may be a significant source of downtime for the load handling device.

To alleviate the problem of charging downtime, the load handling device may be powered by an exchangeable battery. When the battery in the load handling device is depleted, the depleted battery is exchanged for a fully charged battery and therefore the charging downtime is reduced to the time it takes to exchange the battery, rather than the time to charge the battery.

Figure 6(a) shows a rechargeable battery 80 received within a battery compartment 70 of the bot 25.

The lifting assembly 33 and the container-holding assembly 37 have been omitted from view for clarity.

The battery 80 provides electrical power to one or more components of the bot 25, such as the lifting assembly 33, the container-holding assembly 37, and the driving assembly. The battery 80 may be of any suitable rechargeable battery chemistry such as lithium-ion, lithium iron phosphate, nickel metal hydride, nickel-cadmium, etc. The battery 80 comprises an outer casing which houses the cells of the battery 80. To facilitate handling of the battery 80, the outer casing comprises one or more engagement features 81 for being engaged by the end effector of a robotic arm to allow the robotic arm to move the battery 80 into and out of the battery compartment 70. The engagement feature 81 may be a simple protruding feature such as a handle that can be gripped by an end effector comprising a gripping assembly, or may be part of a more complex battery retention mechanism for releasably locking the battery 80 in the battery compartment 70.

The battery compartment 70 is externally exposed at the top of the bot 25 such that the battery 80 can be received in a downwards direction from a location above the external body 27 of the bot 25. In this illustrated example, the battery compartment 70 is located within the external body 27 of the bot 25 and comprises an opening in a top surface of the external body 27 to allow the battery 80 to be moved into and out of the battery compartment 70. In alternative examples, the battery compartment may be located partially within the external body 27 of the bot 25 (i.e. the battery compartment extends past the top surface of the external body 27) or located outside the external body 27 of the bot 25 (e.g. on top of the top surface of the external body 27 of the bot 25).

Figure 6(b) shows a schematic cross-section view of the battery 80 within the battery compartment 70. The battery 80 comprises one or more electrical connectors 82 and the battery compartment 70 comprises one or more corresponding electrical connectors 72 which are electrically coupled (directly or indirectly) to the components of the bot 25 that are to be powered by the battery 80. The electrical connectors 82, 72 are configured to electrically couple to each other when the battery 80 is inserted into the battery compartment 70. The electrical connectors 82, 72 can be any suitable electrical connector for delivering power once connected. The electrical connectors 82, 72 may be blind mate connectors, which physically connect via the action of moving the battery 80 into the battery compartment 70.

Application in a battery charge station Figure 7 illustrates a charge station 50 for charging and exchanging rechargeable batteries in load handling devices, in (a) perspective view, and (b) plan view. The charge station 50 comprises a cabinet 52, illustrated with some side panels removed for visibility of the components within. Charging bays 54 are located in the cabinet, each with a top-facing opening configured to receive a battery. Charger racks 56 are located inside the cabinet 52, and chargers in the charger racks 56 are connected to the charging bays 54 in order to charge batteries inside the charging bays. Each charging bay 54 has a connector 66 to establish an electrical connection to a corresponding connector on a battery received within the charging bay. A fan 64 is provided for cooling of the chargers in the charger racks 56.

A robot arm 58 is mounted on top of the cabinet 5. The robot arm 58 can to remove a battery from a load handling device, insert a battery into a load handling device, and move a battery between a load handling device and the charging bays.

The charge station 50 is provided with a control unit 60, through which a user can see information relating to the charge station and the batteries (for example, the state of charge of batteries in the charging bay), and issue commands (for example, to instruct the robot arm to move a battery from a charging bay into a load handling device). The control unit 60 may comprise a processor, display unit, and input device, for example a touchscreen.

In addition to the charging bays 54, the charge station is provided with a non-charging buffer bay 62 for temporary storage of a battery.

Figure 8 illustrates a battery 80 in two different perspective views. The battery is provided with four corner guides 78 to help guide the battery into a charging bay 54 or into the battery compartment 70. In Figure 8(a) the engagement feature 81 can be seen on the top of the battery 80. In Figure 8 (b) the underside of the battery 80 can be seen, with the connector 82. The connector 82 in the battery 80 is able to connect to a corresponding connector 66 in a charging bay 54 in order to establish an electrical connection and charge the battery. The connector 82 in the battery can also connect to the corresponding electrical connector 72 in the battery compartment 70 in a load handling device 25 in order to establish an electrical connection and provide power to the load handling device 25.

Figure 9 is a more detailed view of the electrical connector 82, in (a) perspective view, (b) side view, and (c) top view. The electrical connector comprises a plate 83, upon which is mounted a pair of alignment pins 84. In the centre of the plate 83 are arranged a data connector 85 and a power connector 86. On either side of the data connector 85 and power connector 86 are a pair of LMFB (last mate first break) connectors 87, which give a positive indication of when the electrical connector 82 of the battery 80 is connected to the corresponding electrical connector 66 in a charging bay. The LMFB connectors 87 monitor the connection status of the electrical connector 82 of the battery 80 and the corresponding electrical connector 66 in the charging bay. Recesses 88 are provided to receive corresponding protrusions in the electrical connector 66, to further ensure that the connection is maintained.

Figure 10 illustrates a charging bay 54 showing the electrical connector 66. Two of the side walls of the charging bay 54 have been removed for visibility. Along the four vertical edges of the charging bay, connecting the side walls, are corner guides 79. These corner guides engage with the corner guide s78 on the battery to help guide the battery into the charging bay. The electrical connector 66 comprises an alignment plinth 91, which supports and locates the electrical connections. Within the plinth are two recesses 94 for locating the alignment pins 84 of the battery electrical connector 82.

Figure 11 is a more detailed view of the charging bay electrical connector 66, in (a) perspective view, (b) side view, and (c) top view. The alignment plinth 91 supports and locates the electrical connections. Two recesses 94 are located in the alignment plinth 91. In the centre of the alignment plinth 91 are a data connector 95 and power connector 96. On either side of the data connector 95 and power connector 96 are a pair of LMFB connectors 97. A pair of protrusions 98 are provided, to be received in the corresponding recesses 89 in the battery electrical connector 82.

In use, as the battery 80 is lowered into the charging bay 54, the alignment pins 84 of the battery electrical connector 82 are received within the recesses 94 in the alignment plinth 91 of the charging bay electrical connector 66. This helps to align the positions of the battery electrical connector 82 and the charging bay electrical connector 66 to allow the two connectors to engage. Once the ends of the alignment pins 84 are received in the recesses 94, as the pins 84 move further into the recesses 94 the protrusions 98 on the charging bay electrical connector 66 enter into the recesses 88 in the battery electrical connector 82. This helps to further align the connectors and ensure that the connection is stable. Next the power connector 96 (pins) of the charging bay electrical connector 66 engages with the power connector 86 (sockets) of the battery electrical connector 82, to enable transfer of power from the charging bay 54 to the battery 80. The data connector 96 (pins) of the charging bay electrical connector 66 engages with the data connector 86 (sockets) of the battery electrical connector 82, to enable transfer of data (for example, data from the BMS of the battery 80 to the charging bay 54).

Finally, the LMFB connectors 84, 94 connect in order to monitor the status of the electrical connection and confirm that the electrical connection is active.

Figure 12 illustrates one of the charger racks 56 illustrated in Figure 7, with chargers 110, contactors 120, and a control module 112. The contactors 120 are mounted on top of the charging rack 56 and arranged in pairs, with one of each pair of contactors connected to a charger 110 and the other of the pair connected to a charging bay. Each pair of contactors is connected with a bus bar 126. The charger rack 56 contains two chargers 110, which provide power via the contactors 120 to two charging bay electrical connectors 66 in two charging bays (not shown). Both charging bays are served by the same control module 112. The battery charge station 50 illustrated in Figure 7 has ten charging bays 54, so five charger racks 56 are provided in total, each charger rack 56 having a pair of chargers 110 providing power to a pair of charging bays 54.

The contactors 120 are connected to the charging bay electrical connectors 66 via charging bay power cables 114, and to the chargers 110 by charger power cables 118. The data connectors of the charging bay electrical connectors 66 are connected to the control module 112 via charging bay data cables 116. The contactors 120 are provided with coil connection tabs 122, which are connected to the control module 112. Auxiliary switch connectors 124 are provided on top of the contactors 120 between the two main power contacts, and also connected to the control module 112.

The contactors are normally open (NO) contactors, i.e. the switch is open in the absence of a signal to close the switch from the control module 112. To energise the contactors, a signal from the control module 112 is sent to the contactors 120 via the coil connection tabs 122. On receiving the signal, the contactors 120 complete the circuit by providing an electrical connection between the charging bay power cables 114 and the charger power cables 118. The chargers 110 can then provide power to the charging bay connectors 66, which provide power to the batteries received within the charging bays.

Figure 13 is a detailed view of the contactors 120, with the cables connecting to the control module not shown for ease of visualisation. In each pair of contactors 120 there is a charger side contactor 120a and a battery side contactor 120b. The charger side contactor 120a has two main power contacts 128a, 128b, and the battery side contactor 120b has two main power contacts 130a, 130b.

The charger power cable 118 ends in a tab that connects to the main power contact 128a on the charger side contactor 120a. The other main power contact 128b on the charger side contactor 120a is connected to the main power contact 13013 on the battery side contactor 120b via a busbar 126. The other main power contact 130a is connected to a tab on the end of the charging bay power cable 114.

Coil connection tabs 122 are connected to the control module via cables (not shown). Auxiliary switch connectors 124 are provided between the two main power contacts on the contactors 120, and connected via cables (not shown) to the control module for the purpose of monitoring the switch status.

The coils of the contactors 120 are enclosed with in a top cover 132 and mounting frame 134. The contactors 120 are mounted onto the top surface of the charger rack 56 via mounting holes on the underside of the mounting frame 134.

When the coil connection tabs 122 on both the charger side contactor 120a and the battery side contactor 120b receive a signal from the control module (cables not shown), the coils inside both contactors 120a, 120b are energised, the contacts are closed, and the circuit is completed. Power can then flow from the charger via the charger cable 118, charger side contactor 120a, busbar 126, battery side contactor 120b, and charging bay power cable 114 to provide power to a battery received within the charging bay.

Claims (15)

1. Claims 1. A method for condition monitoring of a component in a circuit, the method comprising the steps of: i) determining a voltage drop across the component; ii) integrating the voltage drop over a given period of time to calculate an energy metric representative of the energy dissipated by the resistance of the component over the period of time; iii) comparing the energy metric to a predetermined threshold energy metric; and iv) if the energy metric is greater than the predetermined threshold energy metric, deeming that the component has overheated.
2. 2. The method of claim 1, further comprising the step of: v) if the component is deemed to have overheated, switching off the power supply to the component
3. 3. The method of claim 2, further comprising the step of: vi) if the component is deemed to have overheated, indicating that an error has occurred.
4. 4. The method of any one of the preceding claims, wherein the predetermined threshold energy metric is calculated based on an expected energy metric representative of the cumulative energy dissipated by the nominal resistance of the component over the period of time.
5. 5. The method of claim 4, wherein the expected energy metric is calculated by: i) determining a nominal voltage drop across the component; and ii) integrating the nominal voltage drop over the given period of time.
6. 6. The method of any one of claims 1 to 3, wherein the predetermined threshold energy metric is calculated by multiplying the expected energy metric by a factor.
7. 7. The method of claim 6, wherein the factor is in the range 3 to 10.
8. 8. The method of any one of claims 1 to 3, wherein the predetermined threshold energy metric is calculated based on a permitted temperature increase of the component.
9. 9. The method of claim 8, wherein the predetermined threshold energy metric is calculated by multiplying the permitted temperature increase of the component by the heat capacity of the component.
10. 10. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to any preceding claim.
11. 11. A charger for charging a rechargeable power source, comprising: a circuit comprising a power supply and a contactor for switching power to the rechargeable power source; and a controller configured to carry out the method of any of claims 1 to 9.
12. 12. The charger of claim 11, wherein the charger is configured to charge the rechargeable power source in constant current mode.
13. 13. A charge station for charging a rechargeable power source in a load handling device, the charge station comprising: one or more chargers as defined in claim 11 or claim 12; and one or more charging bays configured to removably receive the rechargeable power source, each of the one or more charging bays being configured to electrically couple the rechargeable power source to a respective charger.
14. 14. The charge station of claim 13, further comprising a transfer mechanism configured to move the rechargeable power source between the load handling device and the charging bays.
15. 15. A storage and retrieval system comprising: a) a grid framework structure comprising: i) a track system comprising a plurality of tracks arranged in a grid pattern; ii) a supporting framework structure supporting the track system; and iii) a plurality of stacks of storage containers arranged in stacks a plurality of storage columns located below the track system; b) one or more load handling devices for lifting and moving the storage containers, each load handling device comprising: i) a driving assembly configured to move the load handling device on the track system; ii) an exchangeable rechargeable power source configured to power the driving assembly; Hi) a container-holding assembly configured to releasably hold a storage container from above; and iv) a lifting mechanism configured to raise and lower the a container-holding assembly; c) one or more charge stations as defined in claim 14.