Drive system for a patient lift

Abstract

A drive system (100) for a patient lift. The drive system comprises: a cylinder (321) configured to control vertical movement of a patient support mounting device (11) of the patient lift via a load bearing member (12); at least one motor (270) adapted to drive the cylinder (321), each motor (270) being connected to a motor shaft gear (227); and a transmission (228) connecting the motor (270) to the cylinder (321), the transmission (228) being adapted to transfer torque from the motor (270) to the cylinder (321).

Description

Technical Field

[0001] The present invention relates to a drive system for a patient lift. The present invention also relates to a patient lift comprising such a drive system. Furthermore, the present invention relates to a method for controlling the torque applied by each of at least two motors comprised in the drive system. Background Art

[0002] Patient lifts (also known as patient hoists) are commonly used to raise, lower, and transfer disabled or otherwise mobility-impaired patients. Two common types of patient lifts are strut-mounted lifts (also known as floor lifts) and ceiling lifts. Floor lifts typically have a lifting assembly that can be disposed at the upper end of a strut. The strut has a wheeled base, which allows the lift to be moved along the floor to different positions.

[0003] The lifting member can be in the form of a strut, such as a two-point attachment strut, a three-point attachment strut, a four-point attachment strut, a five-point attachment strut, or a powered strut for adjusting the angle of the strut, to support a patient harness or sling descending from the lifting assembly on a belt or cable. The belt or cable is wound around a powered cylinder to raise and lower the patient harness or sling.

[0004] For example, the lift can be pushed to position the hoist assembly and the lifting member above or adjacent to the patient. The lifting member can then be lowered to receive the patient, and subsequently the lifting member and the patient can be raised so that they can be pushed elsewhere to be lowered and placed. Ceiling lifts can be used in a similar manner, but the lifting assembly is movably engaged to a ceiling-mounted track such that the lifting assembly can be moved along the track from one position to another.

[0005] A ceiling lift can be described as a motor unit capable of moving along a track, with a flexible member attached to a strut. The motor unit typically includes a transmission, a battery, and a control module.

[0006] Transmissions are subject to many challenges. For example, a transmission needs to be able to lift and lower a patient, hold the patient at a prescribed height for a certain period of time, and lower the patient. In addition, the transmission needs to be able to lift and support a weight of approximately 450 Kg.

[0007] To support such a large weight, large motors capable of providing a high amount of torque are often used. Such motors can even handle very heavy loads. However, large motors are typically expensive and consume a large amount of electricity.

[0008] To save costs and electricity, some manufacturers use small motors capable of delivering high RPMs. To enable a small motor to support and lift a higher load, the RPM is typically reduced and the torque is increased through different types of transmissions.

[0009] Such transmission systems are typically complex and space-consuming. Additionally, due to the reliance on a fixed transmission system, the motor unit may lack flexibility in adapting to different applications (i.e., different types of patient lifts). In view of the above, there is a need for a transmission system associated with low cost, high efficiency, and flexibility. Summary of the Invention

[0010] According to one aspect, a drive system is provided. The drive system is for a patient lift. The drive system includes a cylinder configured to control vertical movement of a patient support mounting device of the patient lift via a load-bearing member. The drive system further includes at least one motor adapted to drive the cylinder, and each motor is connected to a motor shaft gear via an output motor shaft.

[0011] Furthermore, the drive system includes a transmission connecting the motor and the cylinder. The transmission is adapted to transfer torque from the motor to the cylinder.

[0012] The transmission includes a transmission interface adapted to interact with the motor shaft gear. The transmission interface is configured to receive the motor shaft gear in at least two configurations. Each configuration is associated with the orientation of the output motor shaft relative to the transmission interface.

[0013] According to one aspect, a patient lift is provided. The patient lift includes a drive system, a patient support mounting device, and a load-bearing member. The patient support mounting device is connected to the drive system via the load-bearing member.

[0014] According to one aspect, a method is provided. The method is for controlling the torque applied by each of at least two motors included in a drive system. The drive system is configured to control vertical movement of a patient support mounting device.

[0015] The method includes obtaining the torque applied by each of the motors; determining at least one torque deviation value, which is the difference between the torques applied by each of the motors; and adjusting the torque applied by at least one of the motors to compensate for the determined at least one torque deviation value.

[0016] According to one aspect, a computer program product is provided. The computer program product is configured to, when executed by a control module, perform a method for controlling the torque applied by each of at least two motors.

[0017] Other objects and features of the present invention will become apparent from the following detailed description of embodiments of the present invention. Brief Description of the Drawings

[0018] The present invention will be described with reference to the accompanying drawings, in which:

[0019] Figure 1a is a perspective view of an element of a patient lift system.

[0020] Figure 1b is a perspective view of an element of a patient lift system.

[0021] Figure 2 A drive system according to an embodiment implemented in a patient lift system is depicted.

[0022] Figure 3 is a partial longitudinal sectional view of a drive system according to an embodiment.

[0023] Figure 4 is an exploded view of a drive system according to an embodiment.

[0024] Figure 5a is a perspective view of a drive system according to an embodiment.

[0025] Figure 5b is a perspective view of a drive system according to an embodiment.

[0026] Figure 5c is a perspective view of a drive system according to an embodiment.

[0027] Figure 6a is a perspective view of a drive system according to an embodiment.

[0028] Figure 6b is a perspective view of a drive system according to an embodiment.

[0029] Figure 6c is a perspective view of a drive system according to an embodiment.

[0030] Figure 7 is a schematic view of a drive system according to an embodiment.

[0031] Figure 8 is a perspective view of a locking arrangement and a motor of a drive system according to an embodiment.

[0032] Figure 9 is a block diagram of a drive system according to an embodiment of the present invention.

[0033] Figure 10 is a schematic flow chart of a method for controlling the torque applied by each of at least two motors according to an embodiment of the present invention.

[0034] Figure 11a is a time diagram of a pulse width modulation supplied to a motor according to an embodiment of the present invention.

[0035] Figure 11b is a time diagram of the torque applied by two motors according to an embodiment of the present invention. DETAILED DESCRIPTION

[0036] Figures 1a and 1b illustrate non - limiting examples of elements of a patient handling system with a patient lift. The patient lift can be in the form of a patient ceiling lift. In Figure 1a, the patient support mounting device 11 is connected to the lifting device 13 via a load - bearing member 12. The lifting device 13 can be arranged to be movable along a track 14. Thus, the lifting device 13 can engage with the track 14, for example, be movably connected to the track 14. The lifting device 13 can move along the track 14, preferably in two directions. The lifting device 13 can be in the form of a trolley that is capable of moving along the said track 14.

[0037] The patient lift can include a drive system, which will be described further with reference to Figures 2 to 7 The lifting device can include a drum for winding the load - bearing member 12 and a motor and a transmission for driving the drum. The load - bearing member 12 can be wound around the drum to lower and raise the patient support mounting device 11. The drive system can be included in the lifting device.

[0038] In one embodiment, the lifting device 13 includes wheels for interfacing with the track 14. In one embodiment, the lifting device 13 is slidably connected to the track 14.

[0039] The patient support mounting device 11 can be a strut or a boom. The load - bearing member 12 can be a flexible member, such as a belt. As shown in Figure 1b, the patient support 15 can be a sling. The patient support mounting device 11 can be connected to the load - bearing member 12 via a connection unit 26. The connection unit 26 can be a quick - connector, i.e., the connection unit 26 is adapted to receive the load - bearing member 12 in a releasable manner.

[0040] The patient support mounting device 11 can include an attachment element 19 for attaching the patient support 15 to the patient support mounting device 11. The attachment element can include a hook with a latch.

[0041] The lifting device 13 is configured to move the patient support mounting device 11 between a raised position closer to the lifting device 13 and a lowered position farther from the lifting device 13. Thus, the lifting device 13 can be configured to vertically move the patient support mounting device 11 between the raised position and the lowered position.

[0042] Although Figures 1a to 1b the patient lift in

[0043] Figures 2 to 7Aspects of an embodiment of a drive system implemented in the patient lift depicted in FIG. 1 are disclosed.

[0044] Figures 2 to 4 A drive system according to an embodiment is depicted. The drive system 100 includes a cylinder and a transmission, which may be included within a housing 213'. Accordingly, the drive system 100 includes the housing 213'. The drive system 100 also includes at least one motor 270. Figure 3 A portion of the drive system 100 without the housing 213' is disclosed. A portion of the transmission and the output motor shaft 274 are disposed within the housing 213'. The drive system includes a locking arrangement 200 to be further described with reference Figure 8 to below.

[0045] Figure 4 An exploded view of the drive system is disclosed. The drive system includes a cylinder 321. The cylinder is configured to control the vertical movement of the patient support mounting device 11 via a load-bearing member 12. The patient support mounting device 11 is connected to the lifting device 13, 213 via the load-bearing member 12. As previously described, the cylinder 321 is adapted to wind and unwind the load-bearing member 12. Accordingly, the cylinder is adapted to be connected to the load-bearing member 12. The load-bearing member may be a flexible member, such as a wire, cable, or rope.

[0046] The drive system 100 also includes at least one motor 270. The at least one motor 270 is adapted to drive the cylinder 321. As depicted, the motor may be disposed orthogonally to the cylinder 321. Each of the at least one motor 270 is connected to a motor shaft gear 227 via an output motor shaft 274.

[0047] The output motor shaft 274 is disposed between the motor shaft gear 227 and the motor 270. In one embodiment, the motor shaft gear 227 is connected to the motor 270 via an additional gear. In one embodiment, the motor shaft gear 227 may be directly connected to the motor 270. Accordingly, the motor 270 may be directly connected to an input motor shaft that includes a gear, thus forming the motor shaft gear 227. In one embodiment, the motor shaft gear 227 may be connected to an input shaft directly connected to the motor.

[0048] The drive system includes a transmission 228. The transmission 228 connects the motor 270 and the cylinder 321. Accordingly, the motor 270 and the cylinder 321 are connected via the transmission 228. The transmission 228 is adapted to transfer torque from the motor 270 to the cylinder 321.

[0049] The transmission 228 includes a transmission interface 220. The transmission interface 220 is adapted to interact with the motor shaft gear 227. In other words, the transmission interface is adapted to interact with the motor shaft gear 227 such that the cylinder 321 is driven by the motor 270.

[0050] The transmission 228 includes a transmission interface 220. The transmission interface 220 is adapted to interact with the motor shaft gear 227. The transmission interface 220 is configured to receive the motor shaft gear 227 in at least two configurations. Each configuration is associated with the orientation of the output motor shaft 274 relative to the transmission interface 220.

[0051] In the field of patient lifts, depending on the application of the patient lift and the weight and mobility of the patient to be carried by the patient lift, the requirements for the drive system can vary greatly. The transmission potentially can receive torque from at least one motor in more than one way, i.e., the configurations enable a modular solution in which more than one motor can be utilized or the positioning of the motor can be changed according to the available space. Thus, a drive system is achieved that allows increased flexibility in use.

[0052] In this document, a configuration is defined as the position where the motor shaft gear 227 interfaces with the transmission interface 220. Thus, the position of the motor shaft gear 227 relative to the transmission interface 220 is provided by the corresponding orientation (i.e., direction and position) of the output motor shaft 274 relative to the transmission interface 220.

[0053] Thus, the transmission interface 220 is adapted to directly engage with the motor shaft gear 227, i.e., is adapted to be directly connected to the motor shaft gear 227.

[0054] The transmission interface 220 can be in the form of one or more gears or pulley wheels, etc.

[0055] In one embodiment, the transmission interface 220 includes an input transmission gear. The input transmission gear 323 is adapted to interact with the motor shaft gear 227.

[0056] In one embodiment in which the drive system 100 includes more than one motor 270, the input transmission gear 323 is adapted to interact with a first motor shaft gear 227 connected to a first motor and a second motor shaft gear 227 connected to a second motor. This allows for a simple installation of the drive system and is space-saving and less complex compared to other modular drive systems for patient lifts.

[0057] In another embodiment, the transmission interface 220 can include a plurality of input transmission gears 323. Thus, a first input transmission gear 323 can be adapted to interact with a first motor shaft gear 227 connected to a first motor 270. A second input transmission gear 323 can be adapted to interact with a second motor shaft gear 227 connected to a second motor 270.

[0058] In one embodiment, the input transmission gear 227 may be arranged orthogonally to the cylinder 321. Accordingly, the engaging portion of the input transmission gear 227 may extend orthogonally to the cylinder 321. As Figure 4 depicted, the input transmission gear may be a sun gear. Accordingly, the outer circumference of the sun gear may extend orthogonally to the cylinder 321.

[0059] Further referring to Figure 4 , the motor shaft gear 227 and the input transmission gear may form a worm drive. As is well known to those skilled in the art, a worm drive is formed by a worm gear and a worm wheel. The worm wheel is arranged orthogonally to the worm gear.

[0060] In one embodiment, the motor shaft gear 227 may be a worm gear. Accordingly, the input transmission gear 323 may be a worm wheel. In one embodiment, the motor shaft gear 227 may be arranged orthogonally to the input transmission gear 323. This allows the input transmission gear 323 to receive the motor shaft gear 227 in different configurations in a space-saving and uncomplicated manner.

[0061] In an alternative embodiment, the motor shaft gear 227 may be a worm wheel, and accordingly the input transmission gear 323 may be a worm gear.

[0062] The transmission 228 may further include an output gear 322. The output gear 322 is fixed to the cylinder 321. The output gear 322 is connected to the transmission interface 220 to receive torque from the motor shaft gear 227. Accordingly, the output gear is arranged between the transmission interface 220 and the cylinder 321 to transfer torque between the transmission interface 220 and the cylinder 321.

[0063] The output gear 322 may include an annular wheel. The annular wheel is fixed to the cylinder 321. Accordingly, a more compact drive system is achieved.

[0064] The output gear 322 may be coaxial with the cylinder 321.

[0065] In one embodiment, the annular wheel may be an integral part of the cylinder 321.

[0066] In one embodiment, the transmission 228 may include a planetary gear 326. The planetary gear 326 meshes with the annular wheel 322. The planetary gear 326 is arranged between the transmission interface 220 and the annular wheel 322.

[0067] Figures 5a to 5c Various embodiments of the drive system are depicted. As can be seen in the drawings, the transmission interface 220 is configured to receive the motor shaft gear 227 in at least two configurations. Each configuration is associated with the orientation of the output motor shaft 274 relative to the transmission interface 220.

[0068] Figure 5a depicts a drive system in which a transmission interface 220 receives a motor shaft gear in one of at least two configurations. The output motor shaft 274 can have an orientation orthogonal to the cylinder 321 in the at least two configurations. As described Figure 5a as visible, the orientation of the output motor shaft 274 associated with the depicted configuration of the transmission interface and the motor shaft gear is substantially orthogonal to the cylinder.

[0069] In an alternative embodiment, the orientation of the output motor shaft 274 can have any other orientation relative to the transmission interface 220, however such a solution requires additional gears and has less benefit.

[0070] Figure 5b depicts a drive system in which a transmission interface 220 receives a motor shaft gear in another of at least two configurations. As described Figure 5b as visible, the output motor shaft 274 in one configuration is oriented orthogonally relative to the output motor shaft 274 in another configuration. Thus, Figure 5a the first configuration depicted is associated with an orientation of the output motor shaft orthogonal to the orientation of the output motor shaft, and the second configuration is associated with the orientation of the output motor shaft.

[0071] Figure 5c depicts a drive system including two motors. The input motor gear shaft 227 of the first motor has a first orientation, and the input motor gear shaft 227 of the second motor has a second orientation. The orientations of the input motor gear shafts are substantially parallel. Thus, the output motor shaft 274 in one configuration is oriented parallel to the output motor shaft 274 in another configuration. Thus, the transmission interface 220 is configured to receive the motor shaft gear 227 in at least two configurations. One of the at least two configurations is associated with the orientation of the output motor shaft 274. Another of the at least two configurations is associated with the orientation of the output motor shaft 274 that is parallel to the orientation of the output motor shaft in the first output motor shaft 274. Although Figure 5c the drive system is shown as including two locking arrangements 200, it should be mentioned that this is merely one embodiment, and a drive system including two motors 270 can well be formed without any locking arrangements 200, or with only one locking arrangement 200. For example, only one motor 270 can be provided with a locking arrangement 200. The second motor 270 can alternatively be provided with a spacer to replace the locking arrangement 200. Thus, a single locking arrangement 200 provided on one of the motors can be used to brake a drive system including multiple motors by locking the motor shaft gear connected to the one motor.

[0072] The drive system may include a first motor and a second motor 270. Accordingly, the transmission interface 220 is adapted to interact with a first motor shaft gear 227 connected to the first motor 270 and a second motor shaft gear 227 connected to the second motor 270. The first motor shaft gear 227 is connected to the first motor 270 via a first output motor shaft 274. The second motor shaft gear 227 is connected to the second motor 270 via a second output motor shaft 274. The transmission interface 220 is adapted to interact with the first motor shaft gear 227 connected to the first motor 270. The transmission interface 220 is also adapted to interact with the second motor shaft gear 227 connected to the second motor 270.

[0073] Having two motors to drive and control the cylinder has many advantages. This allows the use of smaller motors rather than larger motors to provide high torque to the cylinder. Additionally, having smaller motors allows for the use of less expensive motors. Moreover, having two motors allows for a modular system where smaller electronic components (such as circuit boards) can be used for a variety of applications. Having a single large electric motor requires larger electronic components, which may not be suitable for every implementation.

[0074] In one embodiment, the first motor shaft gear 227 and the second motor shaft gear 227 are parallel. Accordingly, the transmission interface 220 receives the first and second motor shaft gears 227 in configurations associated with first and second orientations of the first and second output motor shafts 274, respectively. The first orientation is parallel to the second orientation. This allows for the implementation of two motors in a space-saving manner.

[0075] In one embodiment, the first orientation and the second orientation may be parallel and opposite. Accordingly, the first output motor shaft may extend in a direction opposite to the second output motor shaft.

[0076] In one embodiment, the first orientation and the second orientation may be parallel and in the same direction. Accordingly, the first output motor shaft may extend in a direction parallel and the same as the second output motor shaft.

[0077] The first motor 270 may be arranged on a first side relative to the transmission interface 220, and the second motor 270 may be arranged on a second side relative to the transmission interface 220. The second side may be opposite to the first side.

[0078] Reference Figures 6a to 6c , the motors 270 may have different sizes and capacities. Accordingly, the transmission interface 220 may be adapted to interchangeably receive the input motor gear shafts 227 connected to the motors 270. This allows the drive system to be implemented in a wide range of patient lifts due to the flexibility of the system. Accordingly, the motors 270, the output motor shafts 274, and the motor shaft gears 227 may be arranged to form a motor module. The transmission interface 220 may be adapted to interchangeably receive the motor module.

[0079] Figure 7 More particularly, a drive system according to an embodiment is schematically depicted.

[0080] The motor shaft gear 227 interfaces with the transmission interface. The transmission interface 220 includes an input transmission gear 323.

[0081] The transmission 228 may include a first gear 325 connected to the input transmission gear 323. The first gear 325 may be coaxial with the input transmission gear. In one embodiment, the first gear 325 may be coaxial with the annular wheel 322. In one embodiment, the first gear 325, the input transmission gear 323, and the annular wheel 322 may be coaxial. The coaxial design of the transmission allows for a more compact transmission capable of transferring sufficient torque to the cylinder.

[0082] The transmission 228 may include an input transmission shaft 431. The input transmission shaft 431 is arranged to transfer torque from the input transmission gear 323 to the first gear 325. Both the first gear 325 and the input transmission gear 323 may be mounted to the input transmission shaft 431.

[0083] The first gear 325 may be connected to the annular wheel 322 via an intermediate gear arrangement. The intermediate gear arrangement is adapted to transfer torque from the first gear 325 to the annular wheel 322.

[0084] In one embodiment, the intermediate gear arrangement includes a first intermediate gear 324. The first intermediate gear 324 interfaces with the first gear 325.

[0085] The intermediate gear arrangement may further include a second intermediate gear 326. The second intermediate gear 326 may be connected to the first intermediate gear 324. The second intermediate gear 326 may be adapted to transfer torque from the first intermediate gear 324 to the annular wheel 322. In one embodiment, the first intermediate gear and the second intermediate gear may be coaxial. In one embodiment, the second intermediate gear 326 may interface with the annular wheel 322.

[0086] In one embodiment, the intermediate gear arrangement includes an intermediate shaft 432. The intermediate shaft 432 may be adapted to transfer torque from the first intermediate gear 324 to the second intermediate gear 326. The first intermediate gear and the second intermediate gear may be mounted to the intermediate shaft 432.

[0087] Further referring Figure 7 , the brake element 329 may be fixedly mounted to the annular wheel 322 and / or the cylinder 321. The brake element 329 may be coaxial with the annular wheel 322. In one embodiment, the brake element 329 may be coaxial with any one or all of the input transmission gear 323, the first gear 325, and the intermediate shaft 431.

[0088] In one embodiment, the transmission 228 may include a planetary gear arrangement. Accordingly, the first gear 325 may be the sun gear of the planetary gear arrangement. Additionally, the intermediate gear arrangement may include a planetary gear. In one embodiment, the first intermediate gear 324 is a planetary gear that meshes with the sun gear (i.e., the first gear 325).

[0089] In one embodiment, at least one of the at least one motors 270 is provided with a locking arrangement 200. The locking arrangement 200 is configured to selectively lock the motor shaft gear 227.

[0090] In one embodiment, each of the at least one motors 270 may be provided with a locking arrangement 200. The locking arrangement 200 is configured to selectively lock the motor shaft gear 227.

[0091] Figure 8 The locking arrangement is described in more detail. The locking arrangement 200 may be configured to switch from a disengaged mode in which the locking arrangement 200 does not lock the motor shaft gear 227 to an engaged mode in which the locking arrangement 200 locks the motor shaft gear 227. This may occur in response to the motor 270 switching from an operating state to a power-off state.

[0092] In one embodiment, the locking arrangement 200 may be configured to switch from the engaged mode to the disengaged mode in response to the motor 270 switching from the power-off state to the operating state.

[0093] In one embodiment, the locking arrangement may include a shape memory alloy element 251 and a locking device 250. The shape memory alloy element is connected to the locking device 250 and is arranged to selectively actuate the locking device 250 to control the locking force on the engagement member 273. The engagement member 273 is mechanically connected to the motor 270 of the patient lift and the load-bearing member 12, i.e., the motor 270 of the patient lift and the load-bearing member 12 of the patient lift. The motor 270 is arranged to raise and lower the patient support mounting device 11.

[0094] In the engaged mode, the shape memory alloy element 251 is in a first configuration, and the locking device 250 is in an engaged position that applies a locking force to the engagement member 273, thereby preventing vertical movement of the patient support mounting device 11.

[0095] In the disengaged mode, the shape memory alloy element 251 is in a second configuration that actuates the locking device 250 to a disengaged position relative to the engagement member 273, thereby enabling the patient support mounting device 11 to move vertically.

[0096] Compared with known patient lifts that implement a locking worm wheel transmission, this allows locking even when a large load is suspended by the patient support mounting device 11 without slow movement. In addition, compared with solenoid-activated mechanical brakes, shape memory alloys allow a more cost-effective and lower power consumption solution. In addition, this allows the locking device and the motor to form a single module. Therefore, since both the motor and the locking function are provided in the form of modules, the adaptability of the drive system is further enhanced.

[0097] As is known in the prior art, a shape memory alloy is an alloy that can be deformed in a cold state but returns to its pre-deformed shape when heated. Shape memory alloys are also known as memory metals, memory alloys, smart metals, smart alloys, or muscle wire in the prior art.

[0098] The shape memory alloy elements 151, 251 can be one of the following: Ag-Cd, Au-Cd, Co-Ni-Al, Co-Ni-Ga, Cu-Al-Ni, Cu-Al-Ni, Cu-Al-Ni-Hf, Cu-Sn, Cu-Zn, Cu-Zn-Si, Cu-Zn-Al, Cu-Zn-Sn, Fe-Mn-Si, Fe-Pt, Mn-Cu, Ni-Fe-Ga, Ni-Ti, Ni-Ti-Hf, Ni-Ti-Pd, Ni-Mn-Ga, Ti-Nb alloys.

[0099] The shape memory alloy element 251 can be a two-way memory effect element. In a first configuration, the shape memory element 251 forms a shape that allows the locking device 250 to be in an engaged position relative to the engagement member 273. In a second configuration, 251 forms a shape that is arranged to force the locking device into a disengaged position relative to the engagement member 273.

[0100] Therefore, the locking device 250 can be moved by the shape memory alloy element 251. Thus, the shape memory alloy element 251 can be arranged to move the locking device 250 between the engaged position and the disengaged position. The shape memory alloy element 251 can be directly attached to the locking device 250.

[0101] In one embodiment, the shape memory alloy element 251 is a muscle wire.

[0102] The shape memory alloy element 251 can be arranged to be electrically connected to at least one power source 340 to selectively switch between the first configuration and the second configuration.

[0103] The locking arrangement is arranged to switch from a disengaged mode to an engaged mode in response to no power being supplied to the motor 270. Thus, the locking arrangement can be used as an emergency brake that actuates in response to the patient lift not being supplied with electricity or power. Once electricity or power is supplied to the motor 270, the locking arrangement switches from the engaged mode to the disengaged mode, which allows normal operation of the patient lift.

[0104] According to one aspect, a patient lift is provided. The patient lift includes a drive system according to any one of the embodiments described previously. The patient lift also includes a patient support mounting device 11 and a load bearing member 12. The patient support mounting device is connected to the drive system by the load bearing member.

[0105] Reference Figure 9 , a simplified block diagram of the drive system 100 is shown. In an embodiment of the drive system 350, at least one motor 270 is controlled by a controller 350. The controller 350 may be included in the drive system 100 or provided as an external control module 350. The control module can be any suitable controller, and the present invention is not limited by the details regarding the control module 350. The control module 350 will typically be operably connected to a power supply 340 and the motor(s) 270. It should be mentioned that the power supply 340 may also be included in the drive system 100 or external to the drive system 100. The power supply 340 can be any suitable power supply 340, and those skilled in the art will know how to implement and / or adapt the disclosed invention to work with any level of direct current (DC), alternating current (AC) current source or voltage source. The control module 350 may also be operably connected to any or all other parts of the drive system 100 to obtain torque readings from, for example, the drum 321. The control module 350 may also be operably connected to a user interface for controlling the patient support mounting device 11. The control module 350 can be implemented using a single control system or can be implemented using a distributed system having sensors and / or controllers distributed throughout the drive system 100 and / or the patient lift. The term operably connected refers to any suitable connection and can be a direct connection, a wired connection, a wireless connection, a connection via a bus, or a connection via an active circuit or logic component.

[0106] The inventors behind the present disclosure have further realized that problems can arise when more than one motor 270 controls the driving of a common cylinder 321, as can be the case in the disclosed drive system 100. If all the motors do not deliver substantially the same amount of torque to the cylinder 321, the motor 270 providing the maximum torque may actually drive any of the other motors 270 in the drive system 100. Therefore, for all the motors 270 in the drive system, the torque contributed by each motor 270 should be approximately the same, unless mechanical complexity is added when transferring torque from each motor 270.

[0107] Typically, the motors 270 of the drive system 100 are controlled by the current supplied to them from a power source 340. The simplest way to control the motors 270 is to use the same controlled current for all the motors 270. A preferred alternative is to control each motor 270 individually, so as to allow, for example, current and safety limits to be applied to each motor 270. On the other hand, when the motors 270 may contribute differently to the driving of the cylinder 321, having more than one motor 270 drive a common cylinder 321 may introduce problems. One motor 270 may apply almost all the torque for driving the cylinder 321, while the other motor(s) may be virtually idle when it comes to torque contribution. This may lead to additional wear of the motor 270 that contributes the most to the driving of the cylinder 321. In such a case, it is also preferred to control each of the motors 270 individually.

[0108] When each motor 270 is controlled individually, each motor 270 is provided with an input power P in , which in can be calculated as the product of the voltage V in supplied to the motor 270 and the current I in . The output power P out from the motor 270 can be described as the torque T provided by the motor 270 multiplied by the speed (revolutions per minute, RPM) of the motor 270, i.e., the number of revolutions. Since the motors 270 of the drive system 100 are linked together, they all have the same speed. Therefore, assuming that all the motors 270 have the same efficiency, any difference in the input power P in between the motors 270 can be attributed to the difference in the torque they provide to the cylinder 321.

[0109] To mitigate these problems, reference will be made to Figure 9Figures 0 to 11 depict a method 400 for controlling the torque applied by each of at least two motors 270 included in a drive system 100. The method 400 can operate on top of, in addition to, or as an extension of another motor control method (such as a method for soft start, controlled braking, etc.). The conceptual idea of the method 400 is to ensure that the force exerted on the drive cylinder 321 is substantially equally shared among all the motors 270 of the drive system 100. This will increase the lifespan of the motors 270 and the drive system 100 because, for example, no motor shaft gear 227 will be subjected to greater stress than the other motor shaft gears 227. Of course, this reason applies to all parts of the drive system 100.

[0110] To balance the torque provided by each motor 270, the torque applied by each motor 270 is obtained 410. The torque can be obtained 410 directly, for example, by using a dynamometer. However, such an instrument is expensive and increases the cost of the motors 270 and / or the drive system 100. An alternative and preferred way to obtain 410 the torque is to estimate the torque based on the current supplied to the motor 270. In many cases, the current I supplied to the motor in is controlled by pulse width modulation (PWM) of the power supply 340. From here on, the term PWM will generally refer to the duty cycle of the PWM, which will be obvious to a person skilled in the art although not specifically stated. The power supply 340 is typically a voltage source that provides a voltage V in which is effectively reduced by PWM such that the input power P to the inductive load of the motor 270 can be accurately controlled. in Since all the motors 270 have the same speed, the inventors have realized that by dividing the average current supplied to the motor 270 by the duty cycle of the PWM, an index or measure proportional to the torque of the motor 270 can be obtained 410. Hereinafter, changing, adjusting, or otherwise adapting the PWM refers to changing the duty cycle of the PWM. The methods for measuring and averaging the input current I in are known to those skilled in the art and can use analog (such as low-pass filtering) or digital averaging of the current. In a drive system having N motors 270, the average current supplied to each motor 270 is denoted as I in , and the corresponding duty cycle of the PWM is denoted as PWM n . Each current I n is divided by the associated PWM n to obtain a torque index T n , as shown in Equation 1 below. n

[0111] T n = I n / PWM n Equation 1

[0112] According to Equation 2, the torque error e n,m can be determined as the difference between motor n and another motor m.

[0113] e n,m = T n - T m = I n / PWM n - I m / PWM m Equation 2

[0114] where n and m refer to specific motors 270 among n motors 270. n can be any number between 1 and ∞, i.e., any number, and thus n and m can be any number between 1 and n.

[0115] In other words, if the drive system 100 includes three motors 270, typically two torque errors e n,m , i.e., e 1,2 , e 1,3 , e 2,1 , e 2,3 , e 3,1 and e 3,2 will be calculated for each motor 270.

[0116] In one embodiment, n in Equation 2 above always refers to the motor with the weakest torque, i.e., T n ≤ T m . In this embodiment, the motor 270 that contributes the least torque to the cylinder 321 will be regarded as the main motor, while the other motors 270 will be regarded as slave motors. The torque of the main motor is the torque that the other motors 270 (slave motors) will use as the target torque when controlling the torque, which will be described in detail in the following section. In this embodiment, only the weakest torque T n needs to be referred to determine the torque error. For example, in a drive system with three motors 270, assume that motor #1 contributes the least torque to the cylinder 321. This means that, in this embodiment, only the torque errors e 1,2 , e 1,3 need to be calculated. Note that the motor 270 determined to be the main motor can change during control. For example, for one of the slave motors, the PWM is at the maximum value and the torque is lower than that of the main motor.

[0117] The torque error can also be referred to as the torque deviation value.

[0118] According to the torque error e n,m, it is possible to determine how each motor 270 contributes to the driving of the cylinder 321. Different control strategies can be adopted. Either the motor 270 that contributes the maximum torque will reduce its torque, or the motor 270 that contributes the minimum torque will increase its torque. Optionally, these strategies can be combined, and the motor(s) 270 that contribute the maximum torque will reduce their torque, and the motor(s) 270 that contribute the minimum torque will increase their torque, such that the torque of each motor converges to an intermediate torque. Depending on the usage, different control strategies can be adopted. For example, if the cylinder 321 is in the process of lowering a patient, there is usually a speed limit that must not be exceeded, and this is typically associated with an upper limit in the PWM duty cycle. Once one of the motors 270 reaches this PWM limit, the other motors are controlled such that they provide the same torque or reach the PWM limit. If the other motors reach the PWM limit while the torques are not the same, the motor 270 that reaches the PWM limit first is controlled to reduce its torque until the motor 270 is substantially the same as the other motors.

[0119] To clarify the necessity of control, reference will be made to Figures 11a to 11b for further explanation. This description gives two motors 270, but those skilled in the art will be able to extend the teachings to control more than two motors 270 after reading this disclosure. The motors 270 are assumed to be of the same model and are delivered according to a common specification. The drive system 100 is controlled to rotate the cylinder 321 such that, for example, the load of a patient is lifted. The acceleration is controlled and follows a linear path until a desired speed is reached, at which point the acceleration stops and the speed remains constant. The speed can be controlled by having a target PWM corresponding to the desired speed. Figure 11a The figure shows how the PWM can vary over time when the cylinder is accelerated for a first period A, after which the speed remains constant during a second period S, until the cylinder is finally decelerated during a third period D. As Figure 11a illustrated, the PWM is applied to the two motors 270, and in Figure 11b , the torques Tl, T2 applied by each of the motors 270 are illustrated. The motor 270 applying torque Tl ( Figure 11b , the dashed line) is illustrated as applying a smaller torque than the motor 270 applying torque T2 ( Figure 11b , the solid line). These torques Tl, T2 are proportional to their respective currents and PWM, as taught in Equation 1. Since the same PWM is provided to the two motors 270, in this example, the current supplied to each motor 270 will exhibit a similar pattern to Figure 11bThe behavior of the torques Tl and T2 illustrated in the figure. The reasons for the different currents (and thus torques) can be, for example, aging, faults, individual differences, etc. As previously mentioned, since the two motors 270 operate at the same speed, thus Figure 11b the differences seen in the figure result in the first motor 270 contributing a smaller torque to the cylinder 321 and thus increasing the wear of the second motor 270. Continuing to refer to Figure 11b , if, on the contrary, each motor 270 is controlled by a separate PWM, then decreasing the PWM of the second motor 270 will decrease the second torque T2, and increasing the PWM of the first motor will increase the first torque Tl. Therefore, by controlling the PWM based on the torque, or more precisely, based on the torque error e n,m (as explained with reference to Equation 2), the PWM can be changed such that all motors 270 contribute substantially the same torque to the cylinder 321.

[0120] Returning to method 400 and Figure 10 , as explained in the previous section, determining 420 the torque error is for adjusting 430 the torque applied by at least one of the motors 270. As understood from the previous section, the torque can be controlled by adjusting the PWM. The adjustment 430 can be achieved by an Adjusted Power Level (APL) of the power level applied to the PWM associated with the motor 270 to be controlled. The APL is used as a factor for the PWM, and the APL can be limited according to the control strategy. For example, if an increase is not allowed, the APL can be limited to 1.0 as its maximum value, and if a decrease is not allowed, the APL can be limited to 1.0 as its minimum value. Preferably, there will be one APL associated with each motor 270 of the drive system 100. In the present disclosure, an APL of 1.0 will typically correspond to no compensation, an APL below 1.0 corresponds to a decrease in the PWM, and an APL greater than 1.0 corresponds to an increase in the PWM. This is not considered a limiting factor, and those skilled in the art will recognize that by, for example, separating the PWM from the APL, the reverse association will be achieved. As a starting value, the APL is preferably 1.0, and then compensation is performed based on the torque error e n,m . The APL can be updated by simply subtracting the associated torque error e n,m from the current APL, but preferably, the torque error e n,m is processed by a P, PI, PD, or PID controller well known in the art.

[0121] Return Figure 10and method 400 for controlling the torque applied by each of at least two motors 270 included in drive system 100. In an embodiment, method 400 can run continuously or for a predefined or configurable number of times. Method 400 can be started, for example, by operating drive system 100 or when movement of one of the motors 270 is detected. As mentioned, obtain 410 the torque applied by each of the motors 270. The obtained torque is used to determine 420 the (multiple) torque errors, which are the differences between the torque applied by the first motor 270 among the at least two motors 270 and the torque applied by each of the other at least two motors 270. This can be done as described above with reference to equations 1 and 2. Based on the determined torque errors, adjust 430 the torque applied by at least one of the motors 270. Adjust the torque to compensate for the determined 420 torque errors. Depending on how method 400 is implemented, the entire error can be compensated, but preferably, a controller (such as a P, PI, PD, or PID controller) is used to smoothly compensate for the torque errors over multiple iterations of method 400.

[0122] In one embodiment of the method, after the determining 420 step or as part of the determining 420 step, the method further includes the step of updating 425 the previously disclosed APL of at least one of the motors 270 of drive system 100. In a preferred embodiment of method 400 performed on a drive system 100 including two or more motors 270, the APL is updated for each of these motors 270.

[0123] In another alternative embodiment, the adjusting 430 step is performed by scaling the torque applied by at least one of the motors 270 with the APL associated with at least one of the motors 270.

[0124] In an alternative embodiment of method 400, the APL of each motor is limited to a maximum value of 1.0. It follows that the torque of the motor 270 that contributes the least torque to the cartridge 321 will be used as the target torque, i.e., the motors 270 that contribute more torque will be associated with an APL < 1.0, thus reducing their PWM and the contributed torque. This means determining which motor 270 contributes the least torque and reducing the torque contributed by the other motors 270 to a torque level substantially the same as the torque of the motor 270 that contributes the least torque.

[0125] In another alternative embodiment of method 400, a speed limit and / or a speed target is applied to drive system 100. The speed limit and / or speed target is typically associated with the resulting rotational speed of cartridge 321, but can be any speed affected by motor 270. In this embodiment, method 400 also includes determining 427 a target current and / or a target PWM associated with the speed limit and / or speed target. This can be achieved, for example, by a predefined or configurable equation or look-up table.

[0126] In yet another alternative embodiment, each motor 270 in motor 270 is controlled 429 based on the determined 427 target current and / or target PWM until one of motors 270 reaches the target current and / or target PWM. When one of motors 270 reaches the target current and / or target PWM, the adjustment 430 step is only applied to the other motors 270, i.e., the motors of drive system 100 that have not yet reached the target current and / or target PWM. The steps of determining 427 the target and controlling 429 the motor can run as part of method 400 or in parallel with method 400.

[0127] Alternatively, when controlling speed, not all motors 270 are controlled to reach the determined 427 target current and / or target PWM. Any motor 270 not targeted to reach the determined 427 target current and / or target PWM can effectively produce a braking effect on the cartridge and act as a generator (depending on the type of motor 270 selected). This can be achieved, for example, by not applying a PWM or current to the motor not targeted to reach the determined 427 target current and / or target PWM, or by applying a PWM or current below the target current / PWM.

[0128] In an alternative embodiment of method 400, the torque difference is not adjusted 430 until the PWM of each motor in the motor is higher than 10%, preferably higher than 20% and most preferably higher than 25%. This is beneficial because the measured average current is divided by the PWM, so for lower PWM duty cycles, any measurement error in the current will more affect the calculated torque error e n,m 。

[0129] In an alternative embodiment of method 400, the control of APL is slower. This may mean that APL or torque error e n,mIt is averaged over a period of time that is the cumulative period of operation of the drive system 100. Herein, the operation of the drive system 100 refers to the operation of at least one of the motors 270, i.e., providing a PWM with a duty cycle greater than 0 to at least one of the motors. The cumulative period of operation can be accumulated only when, for example, the PWM is above or below a PWM threshold, or when the PWM is substantially constant (i.e., when the cartridge 321 is not accelerating). In a further embodiment of the method 400, the torque error is averaged over a cumulative period of operation of the drive system 100, the cumulative period being longer than 30 s, preferably longer than 60 s, and most preferably longer than 120 s. In a further embodiment, the cumulative period of operation is accumulated only when the PWM is above 10%, preferably above 20%, and most preferably above 25%.

[0130] In an alternative embodiment of the method 400, the APL associated with each motor 270 is stored in a permanent manner such that it can be retrieved again, for example, after a power failure. In an alternative embodiment of the method 400, each time there is a power loss, the APL associated with each motor is reset to 1,0.

[0131] The method 400 can be varied, adjusted, or tuned in a variety of ways, and the above presentation is considered to give a general idea of the concept and is not intended to describe in detail all conceivable variations. The embodiments presented above can be combined in any suitable way. After reading this disclosure, those skilled in the art will realize that, for example, the APL can be limited to 1,0 such that only a decrease in the PWM is allowed. One of the motors 270 can be selected as the main motor, and the other motor(s) will be controlled to adjust their respective torques to be as close as possible to the torque of the main motor.

[0132] The method 400 can be executed by any suitable circuit or by a suitable controller that executes software code implementing the method 400.

[0133] In addition to ensuring that all motors 270 contribute equally to the torque of the cartridge 321, the described torque error e n,m or the presented APL can have other uses. If the APL is far from 1,0, this may be an indication of a system failure or damage. The term far from 1,0 is vague, and those skilled in the art will know, after reading this disclosure, which differences, errors e n,m or APL will be considered significant when determining the health of the system. An APL that deviates from 1,0 by 10% may be significant in one system, and a deviation of 25% may be significant in another system. The drive system 100 can be configured to act when the APL or the error e n,mPerform an action when there is a significant difference. The limitation on the action can be predetermined or configurable, and the action taken can be any suitable action, such as generating an alarm or stopping the drive system 100. The drive system 100 can also be configured to track, collect, and / or record data related to the applied torque, error e n,m in the drive system 100, APL, and / or any other parameter, such that statistical analysis can be performed on the data.

[0134] According to one aspect, a computer program is provided. The computer program product is configured to, when executed by a control module, perform a method for controlling the torque applied by each of at least two motors according to any one of the above embodiments.

[0135] Aspect

[0136] The scope of the present invention is defined in the appended claims, and the following aspects will be considered exemplary embodiments of the present invention.

[0137] Aspect 1. A drive system (100) for a patient lift, the drive system comprising:

[0138] A cylinder (321) configured to control the vertical movement of a patient support mounting device (11) of the patient lift via a load-bearing member (12);

[0139] At least one motor (270) adapted to drive the cylinder (321), each motor (270) being connected to a motor shaft gear (227);

[0140] A control module (350) operably connected to the at least one motor (270) and a power supply (340); and

[0141] A transmission (228) connecting the motor (270) to the cylinder (321), the transmission (228) being adapted to transfer torque from the motor (270) to the cylinder (321),

[0142] whereby the transmission (228) includes a transmission interface (220) adapted to interact with the motor shaft gear (227).

[0143] Aspect 2. The drive system (100) according to aspect 1, wherein the transmission interface (220) is configured to receive the motor shaft gear (227) in at least two configurations, each configuration being associated with an orientation of the output motor shaft (274) relative to the transmission interface (220).

[0144] Aspect 3. The drive system (100) according to Aspect 1 or 2, wherein the control module (350) is configured to control the torque applied by the at least one motor (270) by controlling the power supplied from the power source (340) to the at least one motor (270).

[0145] Aspect 4. The drive system (100) according to Aspect 33, wherein the controller is further configured to obtain the torque applied by the at least one motor (270) based on the average current supplied to the at least one motor (270) and the pulse width modulation, i.e., the PWM duty cycle setting.

[0146] Aspect 5. The drive system (100) according to Aspect 3 or Aspect 44, wherein the control module (350) is configured to substantially continuously control the power supplied from the power source (340) to the at least one motor (270).

[0147] Aspect 6. The drive system (100) according to Aspect 5, wherein the control module (350) is further configured to control the power supplied to the at least one motor (270) based on a control parameter including a product part.

[0148] Aspect 7. The drive system according to Aspect 6, wherein the control parameter further includes an integral part.

[0149] Aspect 8. The drive system (100) according to Aspect 6 or Aspect 77, wherein the control parameter further includes a derivative part.

[0150] Aspect 9. The drive system (100) according to any one of Aspects 4 to 8, wherein a speed limit is applied to the drive system (100), and the control module (350) is further configured to:

[0151] Determine a target current and / or a target PWM duty cycle associated with the speed limit; and

[0152] Control the at least one motor (270) until the at least one motor (270) reaches the target current and / or the target PWM duty cycle.

[0153] Aspect 10. The drive system (100) according to Aspect 9, wherein only one of the at least one motor (270) is controlled until the motor reaches the target current and / or the target PWM duty cycle.

[0154] Aspect 11. The drive system (100) according to any one of the preceding aspects includes at least two motors (270), wherein the shaft gears (227) associated with each of the at least two motors (270) rotate at substantially the same revolutions per minute, i.e., RPM.

[0155] Aspect 12. The drive system (100) according to aspect 10, wherein the control module (350) is further configured to:

[0156] Obtain the torque applied by each of the at least two motors (270);

[0157] Determine at least one torque deviation value, the torque deviation value being the difference between the torques applied by each of the at least two motors (270); and

[0158] Adjust the torque applied by at least one of the at least two motors (270) to compensate for the determined at least one torque deviation value.

[0159] Aspect 13. The drive system (100) according to aspect 11, wherein the control module (350) is further configured to update the adjusted power level, i.e., APL, of each of the at least two motors (270) before determining the at least one torque deviation value.

[0160] Aspect 14. The drive system (100) according to aspect 12, wherein the control module (350) is configured to adjust the torque applied by at least one of the at least two motors (270) by scaling the torque applied by the at least one motor (270) associated with the APL of at least one of the motors (270).

[0161] Aspect 15. The drive system (100) according to any one of aspects 10 to 13, wherein the control module (350) is further configured to adjust the torque applied by all motors (270) other than the at least one motor (270) that first reaches the target current and / or target PWM duty cycle when the at least one motor (270) reaches the target current and / or target PWM duty cycle.

[0162] Aspect 16. The drive system (100) according to any one of aspects 10 to 14, wherein the control module (350) is further configured to determine which motor (270) contributes the least torque and adjust the torque to be applied by each of the other motors (270) to a torque substantially the same as the torque contributed by the motor (270) that contributes the least torque.

[0163] Aspect 17. The drive system (100) according to any one of aspects 1010 to 16, wherein the torque applied by each of the motors (270) is controlled by the control module (350) based at least on the PWM duty cycle, and the control module (350) is further configured to start adjusting the torque applied by at least one of the at least two motors (270) when the PWM duty cycle of each of the motors is higher than 10%, preferably higher than 20%, and most preferably higher than 25%.

[0164] The present invention has been described in detail above with reference to embodiments of the present invention. However, as will be readily understood by those skilled in the art, other embodiments are equally possible within the scope of the present invention defined by the appended claims.

Claims

1. A drive system (100) for a patient lift, the drive system comprising: a cylinder (321) configured to control vertical movement of a patient support mounting device (11) of the patient lift via a load-bearing member (12); at least one motor (270) adapted to drive the cylinder (321), each motor (270) being connected to a motor shaft gear (227) via an output motor shaft (274); and a transmission (228) connecting the motor (270) to the cylinder (321), the transmission (228) being adapted to transfer torque from the motor (270) to the cylinder (321), whereby the transmission (228) includes a transmission interface (220) adapted to interact with the motor shaft gear (227), wherein the transmission interface (220) is configured to receive the motor shaft gear (227) in at least two configurations, wherein the output motor shaft (274) is capable of changing its positioning and orientation relative to the transmission interface (220) to form the at least two configurations, such that each configuration is associated with the orientation of the output motor shaft (274) relative to the transmission interface (220), wherein the transmission interface (220) includes an input transmission gear (323) adapted to interact with the motor shaft gear (227), and wherein the transmission (228) includes an output gear (322) fixed to the cylinder (321), the output gear (322) being connected to the transmission interface (220) to receive torque from the motor shaft gear (227), wherein a braking element (329) is fixedly mounted to the output gear (322), and the braking element (329) is coaxial with the output gear (322) and the input transmission gear (323), characterized in that the motor shaft gear (227) and the input transmission gear (323) form a worm drive.

2. The drive system (100) according to claim 1, wherein, The motor shaft gear (227) is a worm wheel and the input transmission gear (323) is a worm gear.

3. The drive system (100) according to claim 2, wherein, The output gear (322) includes an annular wheel fixed to the cylinder (321).

4. The drive system (100) according to any one of claims 1-3, wherein, The orientation of the output motor shaft (274) in the at least two configurations is orthogonal to the cylinder (321).

5. The drive system (100) according to any one of claims 1-3, wherein, The at least one motor (270) includes a first motor and a second motor (270), wherein the transmission interface (220) is adapted to interact with a first motor shaft gear (227) connected to the first motor (270) via a first output motor shaft (274) and a second motor shaft gear (227) connected to the second motor (270) via a second output motor shaft (274).

6. A patient lift comprising the drive system according to any one of claims 1 to 5, a patient support mounting device (11) and a load-bearing member (12), the patient support mounting device (11) being connected to the drive system via the load-bearing member (12).

7. A method (400) for a drive system (100) for a patient lift according to any one of claims 1 to 5, the drive system for controlling the vertical movement of a patient support mounting device (11), the method (400) comprising: Obtaining (410) the torque applied by each of at least two motors (270); Determining (420) at least one torque deviation value, the torque deviation value being the difference between the torques applied by each of the motors (270); Adjusting (430) the torque applied by at least one of the motors (270) to compensate for the determined (420) at least one torque deviation value.

8. The method (400) according to claim 7, wherein, The at least two motors (270) operate at the same speed.

9. The method (400) according to any one of claims 7 to 8, further comprising the step of updating (425) the adjustment power level (APL) of each of the at least two motors (270) after the determining (420) step.

10. The method (400) according to claim 9, wherein the adjusting (430) step is performed by scaling the torque applied by at least one of the motors (270) with the APL associated with at least one of the motors (270).

11. The method (400) according to any one of claims 7 to 8, wherein, Obtaining (410) the torque of each of the motors (270) is based on the average current and pulse width modulation (PWM) duty cycle settings provided to control the respective motors (270).

12. The method (400) according to claim 11, wherein, The drive system (100) is arranged with a speed limit, and the method (400) further comprises: before the adjusting (430) step, determining (427) a target current and / or a target PWM duty cycle associated with the speed limit, and controlling (429) at least one of the motors (270) until the at least one motor reaches the target current and / or the target PWM duty cycle.

13. The method (400) according to any one of claims 7 to 8, wherein, The method (400) is substantially continuously repeated, and the adjusting (430) is based on control parameters including a product part, an integral part, and a derivative part of the determined (420) at least one torque deviation value.

14. The method (400) according to any one of claims 7 to 8, wherein, The determining (420) step further comprises determining which motor (270) contributes the minimum torque, and the adjusting (430) step comprises reducing the torque applied by each of the other motors (270) to a torque substantially the same as the torque contributed by the motor (270) contributing the minimum torque.

15. A computer program product comprising instructions which, when executed by a control module, cause the control module to perform the method according to any one of claims 7 to 14.

Images