CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application Serial No.

62/552,732 entitled "WIRELESS CHARGING METHOD FOR ASSEMBLY LINE" by Shi et al., filed August 31 , 2017, the disclosure of which is hereby incorporated herein by reference in its entirety.

TECHNICAL FIELD

[0002] The disclosure relates generally to wireless charging systems, and, in particular, to wireless charging systems for assembly lines.

BACKGROUND

[0003] Assembly lines typically have a conveyor system which is configured to transport pallets along a fixed path by one or more work stations. The pallets support objects, such as parts, components, devices, and the like. The work stations include automated machines, e.g., robots, which are configured to perform tasks on the objects supported on the pallets as the pallets are moved along the conveyor path.

[0004] Sensors and other electronic devices are often incorporated onto the pallets for various reasons. For example, sensors may be used to detect environmental parameters pertaining to the objects on the pallets, such as temperature, pressure, humidity, etc. Position sensors may be used to indicate the position of the objects and/or the pallets. Electronic devices, such as communication equipment, may also be incorporated onto the pallet to enable wireless data transfer.

[0005] The sensors and electronic devices incorporated into the pallets may be powered by batteries. However, the batteries must be periodically replaced and/or recharged which can be time consuming, especially when considering that hundreds to thousands of sensors and electronic devices may be used on an assembly line. What is needed is an automated method of maintaining power and/or charge to the sensors and other electronic devices utilized on the pallets of an assembly line.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1A is a schematic illustration of an assembly line and wireless charging system arrangement according to one embodiment of the present disclosure.

[0007] FIG. 1 B is a schematic illustration of an assembly line and wireless charging system arrangement according to another embodiment of the present disclosure.

[0008] FIG. 1 C is a schematic illustration of a side view of a portion of the assembly line showing a charging station of the wireless charging system of FIG. 1 or FIG. 2.

[0009] FIG. 2 is a block diagram of the wireless charging system of FIGS. 1 and 2.

[0010] FIG. 3 is a diagram of one type of impedance matching circuit for use with the wireless charging system of FIG. 2.

[0011] FIG. 4A is a schematic illustration of a charging station of the wireless charging system of FIG. 1 or 2 shown fixed to the assembly line.

[0012] FIG. 4B is a schematic illustration of a charging station of the wireless charging system of FIG. 1 or 2 shown supported by a stand. [0013] FIG. 5 is a schematic illustration of a charging station showing feedback to the transmitter.

[0014] FIG. 6 is a flowchart of a charging algorithm for the wireless charging system of FIGS. 1 -2.

[0015] FIG. 7A is a schematic illustration showing the charging region of a transmitter coil divided into a plurality of zones with a single receiver coil in the charging region.

[0016] FIG. 7B is a schematic illustration showing the charging region of a transmitter coil divided into a plurality of zones with two receiver coils in the charging region.

[0017] FIG. 8 is a flowchart of a method of determining impedance matching values for each zone and coil arrangement of FIGS. 7A and 7B.

DETAILED DESCRIPTION

[0018] For the purposes of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the disclosure is thereby intended. It is further understood that the present disclosure includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the disclosure as would normally occur to a person of ordinary skill in the art to which this disclosure pertains.

[0019] The present disclosure is directed to an automatic wireless charging system for an assembly line that enables sensors and other electronic devices being

transported on the pallets along the assembly line to be powered and/or charged without the having to manually replace batteries and/or recharge rechargeable batteries. The system is also directed to controlling the voltages of the charging system to minimize the charge on energy storage components in order to increase the life time of the components.

[0020] Referring to FIG. 1A, an assembly line and wireless charging system 10 according to one embodiment of the present disclosure is depicted. The assembly line includes a conveyor system 12 having one or more conveyor belts, or the like, which are arranged to form a continuous, fixed path. The conveyor system 12 is configured to transport a plurality of pallets 14 along the path. Work stations 16 are arranged along the conveyor path. The pallets 14 are configured to support one or more objects (not shown), such as parts, devices, components, and the like, in order to transport the objects by each of the work stations. The work stations 16 include machines and factory equipment which are configured to perform one or more tasks in relation to the objects on the pallets 14 as the pallets 14 pass by the work station 16.

[0021] Sensors and other electronic devices (See, e.g., FIG. 2, 20) may be incorporated onto the pallets for various reasons. For example, sensors 20 may be used to detect environmental parameters pertaining to the objects on the pallets, such as temperature, pressure, humidity, etc. Position sensors may be used to indicate the position of the objects and/or the pallets. Electronic devices, such as communication equipment, may also be incorporated onto the pallet to enable wireless data transfer.

[0022] The wireless charging system is configured to wirelessly power and/or charge any sensors and electronic devices located on the pallets. The wireless charging system is configured to use near-field magnetic resonance to wirelessly transfer power and/or to charge the electronic devices on the pallets. Near-field magnetic resonance is used because it has high efficiency, low EM radiation, and moderate flexible. A simplified block diagram of a near-field magnetic resonance charging system is depicted in FIG. 2.

[0023] The charging system of FIG. 2 includes a resonator structure comprising a transmitter (TX) resonator 28, also referred to herein as a TX coil, and a receiver (RX) resonator 30, also referred to herein as a RX coil. The TX coil 28 is the primary coil in the magnetic resonance charging scheme and is used to generate an alternating electromagnetic field. To generate the electromagnetic field, a signal generator 22 outputs an alternating signal which is amplified by an amplifier 24 before being fed to the TX coil 28.

[0024] The RX coil 30 is the secondary coil in the magnetic resonance charging scheme. The alternating electromagnetic field generated by the TX coil 28 induces an alternating current in the RX coil 30. This current is used to power and/or charge the electronics 20, e.g., sensors and devices, incorporated into the pallets. A rectifier 34 may be used to rectify the received current before it is supplied to an energy storage device 36. The energy storage device 36 provides power/charge to the sensor 20.

[0025] Impedance matching is a key factor in efficiency for magnetic resonant near- field wireless power transfer. To this end, transmit and/or receive sides of the resonance charging system may include impedance matching networks 26, 32. As is known in the art, impedance matching networks may be used to match the impedances of the transmit and receive coils to improve the efficiency of power transfer. In one

embodiment, a ττ-match network is used for impedance matching. An example of a π- matching network is depicted in FIG. 3. [0026] Referring again to FIG. 2, the current induced in the RX coil 30 is supplied to at least one energy storage device 36. The energy storage device 36 in turn is configured to supply energy to one or more electronic device(s) 20 associated therewith. The energy from the energy storage device 36 may be used to power or charge the associated electronics. Any suitable type of energy storage device 36 may be used, such as capacitors, supercapacitors, ultracapacitors, batteries and the like. In the embodiments described below, the energy storage device 36 is described as a supercapacitor which are known for having a long life and high charging current capability. It is to be understood that other types of energy storage devices may be used as an alternative to or in addition to supercapacitors.

[0027] To implement the resonance charging system, the TX coil 28 is provided at a charging station 18 which is located at a fixed position along the conveyor path, and at least one RX coil 30 is incorporated onto each pallet 14. Although a single charging station with a single TX coil may be used to charge the electronics on the pallets, a plurality of charging stations each having at least one TX coil 30 may be used as depicted in FIGS. 1A-1 C. FIG. 1A shows an embodiment in which a plurality of charging stations 18 are arranged in succession at a single location along the conveyor path. FIG. 1 B shows another embodiment in which a plurality of charging stations 18 are provided at different locations along the conveyor path.

[0028] As can be seen in FIG. 1 C, the TX coils 28 and the RX coils 30 are arranged so that the RX coils 30 pass through the electromagnetic fields generated by the TX coils 28 in the charging stations. Any suitable number and positioning of charging stations and/or TX coils may be used. The charging stations may be fixed on the assembly line with both horizontal and vertical movement freedom to optimize power transfer. The horizontal and vertical adjustments may be made manually by a user of the system or may be made automatically with the appropriate equipment as is known in the art.

[0029] The charging stations 18 with the TX coils 28 can be provided on a support structure 38 attached to the assembly line rails 40 as depicted in FIG. 4A or to a stand 42 that is separate from the assembly line as shown in FIG. 4B. Horizontal and vertical adjustment mechanisms may be incorporated into the support structure or stand. The TX coil 28 can get an implicit feedback using in-band load modulation communication (similar to NFC). Further, the TX side be equipped with wireless radio to receive feedback about charging efficiency directly from the receivers or via the control system 44 as shown in FIG. 5.

[0030] A charging algorithm for the wireless charging system will now be described. The charging algorithm is directed to controlling the voltage across the supercapacitor and the charging current that contributes to the self-heat temperature. Because the life of the supercapacitor may be maximized when less charge is stored, the charging algorithm is configured to minimize the charge on the supercapacitor. Based on the amount of energy on the supercapacitor and the time until the next charging event, the algorithm enables a decision to made as to whether or not to charge the supercapacitor, the amount of energy used to charge the supercapacitor, the time duration to charge, the charging current, with an eye toward prolonging life cycles and minimizing system cost. The values used in the algorithm are computed based on given factory parameters and requirements in the design phase. Then in the operation phase, the algorithm enables real-time charging decisions using the computed values from the design phase.

[0031] Input parameters for the charging algorithm include (i) factory parameters, such as speed of the conveyor belt (Vbeit), time duration between each charging event (tperiod), length of the conveyor belt (L), and minimum separation between objects to be charged (d _spa ce), (ii) sensor parameters, such as operating voltage (V _op ) and operator power (Pioad), (iii) energy storage parameters, such as capacitance (C), leakage resistance (Rieak), maximum current (l _C harge_max), and capacitor voltage (V _cap ), and (iv) transmitter coil parameters, such as diameter of the TX coil (DTX). In addition, the charging algorithm may be configured to utilize a reduced power mode, which gives the option for lowering charging power by increasing the number of transmitters if desired by the end user. A scalar value (a _p0 wer) indicating the amount of power reduction in the reduced power mode is also an input parameter for the charging algorithm.

[0032] The output parameters of the charging algorithm include V _min , lcharge, and arge, as well as #TX. V _m i _n , lcharge, and arge are parameters used to control the operation of the energy storage device. #TX is the number of TX resonators needed to generate the required power. V _m i _n is the minimum voltage of the capacitor that can provide enough energy to the electronic device before the next charging event happen.

Vmin is calculated based on the following equation:

i , ~ ·..., solving for V _min , where

results in the following equation:

[0033] Charge is the current to charge the energy storage device. To reduce the wireless transmit power, the reduced power transfer mode may be enabled, which reduces Uarge while the other parameters (eg. t _C harge) are changed accordingly to achieve the V _m i _n requirement. If the reduced power transfer mode is disabled, arge - Uarge_max. When the reduced power transfer mode is enabled, arge = argejnax / a _powe If the spacing between objects (d _spa ce) is less than the diameter of the TX coil (DTX), then more than one receiver coil may pass under the transmitter coil at the same time. As a result, transmitter power (Uarge) must be increased accordingly.

[0034] The parameter arge is the time needed to charge the energy storage device to an expected voltage which may calculated based on the following equation:

The following equation may be used to calculate #TX.

[0035] A flowchart depicting the logic of the charging algorithm is depicted in FIG. 6. During operation, V _cap is measured in real time. V _m i _n is calculated during the design phase according to the equations described above. According to the flowchart, once a pallet reaches a charging station (step 600), a determination is made as to whether the voltage across the energy storage device (V _cap ), e.g., supercapacitor, is greater than Vmin (step 602). If Vcap is greater than V _m i _n , no charging takes place (step 604). If V _cap is not greater than V _m i _n , the TX coil is activated resulting in charging of the energy storage device (step 606). The position of a pallet and/or RX coil on a pallet may be determined in any suitable manner.

[0036] When it is time to charge, the charge current is based on the computation result in the design section. Because there is efficiency loss during wireless power transfer, the power output of the TX coil can be increased to compensate for the loss so it can deliver the expected current. The efficiency is based on the transmitter design and the distance limit between the transmitter and receiver. The transmitter will not charge the unless the energy storage device cannot provide enough energy to the load before the next charging event. The charging operation is controlled in accordance with the charging current (I charge) and the charging time (t _C harge) computed in the design phase.

[0037] When the target to be charged is moving, the relative impedance changes based on the target position with respect to the TX coil. When impedance is not matched, the wireless power transfer efficiency suffers. Dynamic impedance tuning, used in other work, is not time efficient. An impedance tuning method is proposed herein for improving the power transfer efficiency particularly for moving objects.

[0038] To optimize the impedance tuning, the area under and near the transmitter coil 28, referred to herein as a charging region, is divided into several zones and optimal impedance matching values are computed separately for each zone. FIGS. 7A and 7B illustrate examples of how the charging region under a TX coil may be divided. The charging region is divided into seven zones (n = 7) in FIGS. 7A and 7B. FIG. 7A depicts an example in which one RX coil 30 is passing through the charging region, and FIG. 7B depicts an example in which two RX coils 30 passing through the charging region. [0039] The design phase of the resonance charging system results in a set of impedance values which are used to set the impedance of one or both of the TX coil 28 and RX coil 30 based on the position of the RX coil under the TX coil. The parameters used to calculate the impedance values include (i) the distance between transmitter and receiver (minimum clearance of equipment installation hanging on top of the conveyor belt specified by the factory, d _c i _ea r), (ii) the sizes of transmitter and receiver coils (how to choose the sizes are not in the scope of this work), and (iii) the minimum separation distance between objects to be charged (d _sp ace).

[0040] A flowchart of a method of generating impedance matching values for power transfer based on relative positioning of the TX coil and RX coil is depicted in FIG. 8. First, the charging region is divided into a number of zones, n (step 800). The size of each zone may correspond to the size of the RX coil although not necessarily. Each zone may share some overlapping area with a neighboring zone. Depending on the size of the minimum spacing between RX coils (d _spa ce) relative to the diameter of the TX coil (Djx), single coil arrangements or dual coil arrangements are utilized (step 802).

[0041 ] Impedance matching values are determined for situations in which a single RX coil is located in the charging region (step 804). To determine the impedance matching values under single RX coil conditions, a receiver coil is positioned in parallel to the transmitter coil in a first one of the zones at the fixed vertical separation distance (d _c iear) that will be implemented during operations, and impedance matching values are determined for that zone for the single coil condition. The process is repeated for each zone so that impedance matching values are determined for each zone under single RX coil conditions (step 808). [0042] Impedance matching values are also determined for other RX coil conditions, such as two RX coils being in the charging region (step 806). A similar process is used to determine the impedance matching values for multiple receiver coils. In the case of two receiver coils, the two receiver coils are positioned at the fixed vertical separation distance d _c iear with the two receiver coils being arranged parallel to the transmitter coil and in separate zones which are spaced apart by at least the minimum distance dspace. Impedance matching values are determined for that arrangement of receiver coils. The receiver coils are moved to a different arrangement and impedance matching values are determined for that arrangement and so on (step 808). The impedance matching values may be stored in a memory which is accessible by a controller for the system for use during operations.

[0043] The distance between the centers of each zone is predetermined. However, extremely high resolutions are not necessary as the impedance change is subtle with subtle location change. In the example of FIG. 7A and 7B where the number of zones n = 7, the size of each zone is the size of a receiver coil, and the resolution of the zone is one zone spacing.

[0044] For each transmitter and receiver location described above, impedance matching values may be determined for (i) only the impedance matching network on the TX side, (ii) only the impedance matching network on the RX side, and (iii) the impedance matching networks on both the TX side and the RX side in conjunction. The impedance matching values for each location and condition may be determined in any suitable manner. [0045] During operation, the location and number of RX coil(s) in the charging zone is detected in real time using, for example, sensors, cameras, and the like. Impedance matching values are selected for at least one of the TX side, the RX side, and both the TX side and RX side, based on the location(s) of the RX coil(s) (e.g., which zone(s)) and number of RX coils in the charging region. The appropriate impedance matching network(s) are then adjusted, e.g., switched, so that the selected impedance values are generated. The impedance matching values may be updated as needed as the RX coils move from zone to zone through the charging region so that optimum power transfer efficiency may be achieved regardless of the position of the RX coils under the TX coil. Any suitable type of controller and/or processor may be used to select the impedance matching values and to control the impedance matching networks.

[0046] While the disclosure has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the disclosure are desired to be protected.