Swivel caster with drive wheel

Abstract

A swivel caster comprises a wheel, an electric motor (51) contained in a hub to drive the wheel, and a shaft for connecting the swivel caster to a movable wheeled device and enabling the swivel caster to rotate around a longitudinal axis of the shaft. The swivel caster further comprises a sensor arrangement (65) comprising a rotary encoder arranged in the hub and configured to measure angular acceleration of the wheel, and a controller (64) configured to control drive current provided to the electric motor (51) as a function of the measured angular acceleration. In this way, a swivel caster is provided that can assist an operator in moving a movable wheeled device by an assist torque that depends directly on the force exerted by a person pushing or pulling the movable wheeled device, thereby mirroring the intention of the person.

Description

Technical Field

[0001] The present invention relates to a swivel caster for a movable wheeled device, the swivel caster comprising a wheel driven by an electric motor, and to a movable wheeled device comprising at least one swivel caster. Background Technology

[0002] Mobile wheeled devices (such as hospital beds, shopping carts, wheeled workbenches, trolleys, transport containers, or waste containers) are typically equipped with wheels to enable easy movement. These wheels can be stationary wheels, swivel casters, or a combination thereof. Using swivel casters makes it easier for personnel to guide mobile wheeled devices in the desired direction.

[0003] Because such mobile wheeled devices typically carry considerable weight, they can be difficult for people to push. Therefore, similar to electric bicycles, an electric motor can be used to assist people in pushing the mobile wheeled devices.

[0004] An example of this technology is known from US 2015 / 0216487, which illustrates a medical device in the form of a hospital bed having a base with four wheels. These wheels, or a portion thereof, can be driven by an electric motor arranged on the base. Force sensors are arranged, for example, on a handle or guiding device (which enables the operator to move the medical device) so that the force sensors can detect the force applied by the operator pushing or pulling the medical device. A controller can then activate the electric motor based on the force detected by the force sensors, thereby assisting the operator in moving the medical device.

[0005] However, in the medical device, multiple different components (such as force sensors, controllers, and motors) are placed in different locations within the device. This necessitates separate electrical connections between the force sensors and the controller, as well as between the controller and the motor. Furthermore, a mechanical connection is required between the motor and the wheels. Summary of the Invention

[0006] Therefore, the purpose of embodiments of the present invention is to provide a swivel caster that achieves a simpler solution that eliminates the need for electrical and mechanical connections between multiple components on a movable wheeled device, and that the swivel caster can efficiently drive the wheels of the movable wheeled device in a manner based on the force applied by the operator pushing or pulling the movable wheeled device, thereby assisting the operator in moving the movable wheeled device.

[0007] According to an embodiment of the present invention, the objective is achieved by a swivel caster comprising a wheel, a motor contained in a hub for driving the wheel, and an axle for connecting the swivel caster to a movable wheeled device and enabling the swivel caster to rotate about a longitudinal axis of the axle. The swivel caster further comprises: a sensor arrangement including a rotary encoder disposed in the hub and configured to measure the angular acceleration of the wheel; and a controller configured to control the drive current supplied to the motor based on the measured angular acceleration.

[0008] By placing the motor, the sensor arrangement, and the controller within the swivel caster, the swivel caster can operate autonomously when used with a movable wheeled device, i.e., independently of the circuitry arranged on the movable wheeled device itself. Since the angular acceleration, easily measurable in the swivel caster, is proportional to the linear acceleration of the movable wheeled device using the swivel caster, the angular acceleration, given the weight of the movable wheeled device, is also proportional to the force acting on the movable wheeled device from the outside (e.g., from a person pushing or pulling the movable wheeled device). Furthermore, the auxiliary torque transmitted from the motor in the swivel caster to the movable wheeled device is proportional to the drive current supplied to the motor. Therefore, although the movable wheeled device is driven by autonomous swivel casters, the auxiliary torque used to drive the movable wheeled device directly depends on the force applied to the movable wheeled device by the person pushing or pulling it, thus reflecting the person's intention.

[0009] The swivel caster may include a slip ring configured to establish an electrical connection with a movable wheeled device.

[0010] In one embodiment, the controller is configured to control the drive current supplied to the motor by increasing the drive current supplied to the motor when the measured angular acceleration exceeds a positive threshold; decreasing the drive current supplied to the motor when the measured angular acceleration is below a negative threshold; and maintaining the drive current supplied to the motor constant when the measured angular acceleration is between the negative and positive thresholds. This achieves very stable control of the motor, where irregular walking patterns of personnel pushing or pulling the movable wheeled device using the swivel casters do not affect the control.

[0011] In one embodiment, the swivel caster includes a swivel lock or directional lock configured in a locked position to prevent the swivel caster from rotating, and wherein the controller is configured to drive the motor only when the swivel lock is in its locked position. In this way, it is ensured that current is supplied to the motor only when the swivel caster is locked in the appropriate position (e.g., when the wheel is aligned with the longitudinal axis of the movable wheeled device using the swivel caster).

[0012] In one embodiment, the swivel caster includes a brake configured in a braking position to prevent the wheel from rotating or rolling, and wherein the controller is configured to actuate the motor only when the brake is not in its braking position. In this way, it is ensured that current is supplied to the motor only when the wheel is freely rotating.

[0013] The sensor arrangement can be further configured to measure the angular velocity of the wheels, and the controller is further configured to drive the motor based on the measured angular velocity. As an example, the measured velocity can be used to detect the direction of movement of the movable wheeled device using the swivel casters. Therefore, a positive velocity can indicate that the swivel casters are moving in a forward direction, while a negative velocity can correspondingly indicate that the swivel casters are moving in a backward direction.

[0014] In one embodiment, the swivel caster further includes a tilt detector arranged to determine the component of gravitational acceleration in the drive direction of the wheel, and the controller is further configured to drive a motor of the drive wheel according to the determined component of gravitational acceleration. In this way, the swivel caster can automatically compensate for the additional force required when the movable wheeled device using the swivel caster moves uphill and the reduced force required when moving downhill.

[0015] In this configuration, the controller can be configured to determine a tilt compensation current based on the determined component of gravitational acceleration, and to drive the motor of the wheel using a drive current determined based on the measured angular acceleration in combination with the tilt compensation current.

[0016] In one embodiment, the tilt detector includes a three-dimensional DC-response accelerometer arranged to measure gravitational acceleration relative to a plane perpendicular to the longitudinal axis of the shaft used to connect the swivel caster to a movable wheeled device. Alternatively, the tilt detector may include an angle measuring device arranged to determine an angle between a plane perpendicular to the longitudinal axis of the shaft used to connect the swivel caster to the movable wheeled device and a horizontal plane, and the controller may be further configured to determine a component of the gravitational acceleration based on the determined angle.

[0017] The present invention also relates to a movable wheeled device comprising at least one swivel caster as described above. Attached Figure Description

[0018] Embodiments of the invention will now be described more fully with reference to the accompanying drawings, in which...

[0019] Figure 1 A hospital bed is shown as an example of a movable device, in which swivel casters according to the invention can be used.

[0020] Figure 2 An example of a swivel caster with a drive wheel is shown, the swivel caster being suitable for... Figure 1 The hospital bed

[0021] Figure 3 A cross-section of the top component of a swivel caster with a slip ring is shown.

[0022] Figure 4 A schematic structure of a wheel with an electric motor is shown, the electric motor being contained within... Figure 2 In the hub of the swivel caster,

[0023] Figure 5 A rotary encoder is shown, which has an optical sensor and an optical pattern arranged on a circular annular element.

[0024] Figure 6 Showing the use of Figure 4 An example of a control system for an electric motor.

[0025] Figure 7 An example of a control strategy is shown, which provides control based on the measured angular acceleration. Figure 4 The drive current of the motor,

[0026] Figure 8 Show Figure 6 A control system with several added functions.

[0027] Figure 9 Show Figure 8 A control system that includes a tilt detector.

[0028] Figure 10 The measurement of the gravitational acceleration of a bed placed on a horizontal surface is shown, and

[0029] Figure 11 The measurement of the gravitational acceleration of a bed placed on an inclined surface is shown. Detailed Implementation

[0030] Figure 1 A hospital bed 1 is shown as an example of a movable wheeled device to which the present invention can be applied. It should be noted that the present invention can also be applied to other types of movable wheeled devices, such as shopping carts, wheeled workbenches, trolleys, transport containers, or waste containers.

[0031] The hospital bed 1 has a base 2 with a generally rectangular shape, and a swivel caster is arranged at each corner of the base 2, namely three swivel casters 3, 4 and 5 with non-drive wheels 7, 8 and 9 and one swivel caster 6 with drive wheel 10. The drive wheel 10 is used to assist in the movement of the hospital bed 1, thereby making it easier for personnel to push or pull the hospital bed.

[0032] It should be noted that the approximate rectangular shape defined by the base 2 does not need to be a precise rectangle. Therefore, for example, if the two front wheels are arranged such that the distance between them is less than the distance between the two rear wheels, the base can be slightly trapezoidal. Furthermore, it should be noted that although the base 2 defines an approximate rectangular shape by means of the four corners (where swivel casters are arranged), the base itself can have other forms.

[0033] It should also be noted that, although described here and Figure 1 The embodiment shown is equipped with four swivel casters, that is, three swivel casters with non-drive wheels and one swivel caster with a drive wheel. However, in other embodiments, some or all of the wheels may be arranged as fixed wheels. Furthermore, more than one of the wheels may be drive wheels.

[0034] Two lifting columns 11 and 12, arranged on the base 2, support the bed frame 13, which can be lowered or raised via the lifting columns 11 and 12. Multiple bed sections 14, 15, and 16 on the bed frame 13 can be tilted via one or more linear actuators 17. Furthermore, a power supply 21 is arranged on the bed frame 13 to supply power to, for example, the lifting columns 11 and 12 and the one or more linear actuators 17. The power supply 21 can be a power source connected to a main power supply, a battery-powered power source, or a combination thereof.

[0035] The swivel caster 6 with drive wheel 10 is also connected to power source 21 via cable 22 so that the motor of drive wheel 10 (which will be described below) can be powered. As an alternative to powering the motor in wheel 10 from power source 21 via cable 22, a rechargeable or replaceable battery can be arranged in swivel caster 6.

[0036] A handle or foot pedal 23 is positioned on the base 2 near the swivel caster 6 with drive wheel 10 (as shown here) or on the swivel caster 6 itself. When the handle is in one position (e.g., pushed upwards), the caster can be locked in that position (i.e., prevented from rotating), and when the handle is in another position (e.g., pushed downwards), the wheel 10 can be braked or locked (i.e., prevented from rotating within the caster 6). Alternatively, these functions can be achieved using separate handles / foot pedals.

[0037] Furthermore, the four corners of the rectangular base 2 define a plane 24, which is arranged parallel to the surface on which the hospital bed 1 is placed. Therefore, when the hospital bed 1 is placed on a horizontal surface, plane 24 is also a horizontal plane.

[0038] Figure 2 A swivel caster 6 with a drive wheel 10 is shown in more detail. The swivel caster 6 has a top component 25, which is fixed relative to the base 2 by a mounting rod or mounting shaft 26 having a central axis 27 and being arranged to be received in a mounting hole in the base 2 such that the central axis 27 is perpendicular to the plane 24.

[0039] Drive wheel 10 is mounted to fork carriage 31, which is connected to a fixed top component 25 via a swivel joint (not shown). This swivel joint allows fork carriage 31, and thus wheel 10, to rotate freely 360 degrees about the central axis 27 of mounting shaft 26. Wheel hub 33 is arranged about the central axis 32 of wheel 10. It should be noted that there is a certain offset between the central axis 27 of mounting shaft 26 and the central axis 32 of wheel 10, which allows the swivel caster 6 to align with the direction of movement of the hospital bed. Figure 2 It is also shown that the wheel 10 has a tread 34 and a wheel cover 35, and the electric motor that drives the wheel is arranged behind the wheel cover.

[0040] As described above, the swivel caster 6 is powered via a cable 22 connected to the top component 25. In the top component 25, a slip ring arrangement (which will be described below) ensures that power can be delivered via a cable 36 attached to the fork 31 to the swivel component of the caster 6, i.e., the motor that drives the wheel and other circuitry.

[0041] Figure 3A cross-section of the top component 25 is shown, illustrating an embodiment of a slip ring 41 comprising two annular printed circuit boards. The lower printed circuit board 42 is attached to the swivel component (i.e., the fork 31) of the caster 6 and is provided with a plurality of circular circuit traces 43. The upper printed circuit board 44 is attached to the fixed top component 25 and is provided with a plurality of sliding contacts 45 arranged to contact the circuit traces 43 on the lower printed circuit board 42. Although not shown, the sliding contacts 45 are connected to cable 22, and the circuit traces 43 are connected to cable 36. Alternatively, the circuit traces may be arranged on the upper printed circuit board 44, and the sliding contacts may be arranged on the lower printed circuit board 42, or other contact types may be used.

[0042] like Figure 2 As shown, a hole 37 is arranged in the mounting shaft 26. The hole 37 can receive the shaft of the foot pedal 23, and the caster 6 can be locked in a given position (i.e., prevented from rotating) by a known mechanism (not shown) in the rotating caster 6, and the wheel 10 can be braked or locked (i.e., prevented from rotating in the caster 6).

[0043] Figure 4 A schematic structure of an example wheel 10 with an electric motor 51 is shown, the electric motor being contained in a hub 33. Figure 4 The motor 51 shown is a so-called "outrunner" or "external-rotor" configuration brushless DC motor, in which electromagnets 52 (each electromagnet having a stator winding or stator coil wound around a core) form the center (core) of the motor, while permanent magnets 53 are arranged within a suspended rotor or annular component 54 surrounding the core. The tread 34 of the wheel 10 is arranged on the outside of the annular component 54. It should be noted that... Figure 4 The number of electromagnets 52 and permanent magnets 53 shown is merely an example. Many other combinations can be used.

[0044] Electronic control circuitry 61 (described in detail below) continuously switches the current supplied to the stator windings in each phase of the motor based on signals, for example, from Hall effect sensors (which provide information about the orientation and position of the rotor relative to the stator windings), to keep the motor rotating. This ensures proper commutation of the brushless DC motor 51. The control circuitry, along with other electronic components, can be arranged on a printed circuit board 55, which is fixed to the stator portion of the motor and thus also included in the hub 33.

[0045] To ensure that the motor 51, and therefore the wheel 10, can be driven according to the force acting on the bed 1 from the outside, a rotary encoder is arranged in the wheel 10. The rotary encoder includes an optical sensor 56 arranged on a printed circuit board 55 and an optical pattern 59 arranged on a circular annular element 58 attached to a wheel cover 57, which is similar to the wheel cover 35 on the other side of the wheel 10. This... Figure 5 As shown in the figure. Therefore, the optical sensor 56 is fixed to the stator portion of the motor, while the optical pattern 59 rotates with the rotor portion of the motor, so that the sensor 56 can detect the position of the wheel by passing through the optical pattern 59 during the rotation of the wheel 10.

[0046] Figure 6 An example of a control system for a brushless DC motor 51 used in wheel 10 is shown. In this example, basic control of the motor 51 (i.e., synchronizing the current in the stator windings with the actual position of the rotor magnets) is performed by a BLDC controller 61 and a drive circuit 62 based on signals from a Hall effect sensor 63, which provides information about the position of the rotor magnets relative to the stator coils. This control is well-known and will not be described in detail here. The BLDC controller 61 and drive circuit 62 are mounted on a printed circuit board 55, which... Figure 5 It is also shown in the text.

[0047] It should be noted that since the optical sensor 56 detects the position of the wheel, it also detects the position of the rotor magnet 53 relative to the stator coil 52. When the motor is running, the BLDC controller 61 can also use the signal from the sensor to synchronize the current in the stator winding with the actual position of the rotor magnet. However, the sensor only provides relative position information of the magnet, so the signal from the Hall effect sensor 63 is still needed during motor startup, and it may also be appropriate to occasionally use the Hall element for synchronization while the motor is running.

[0048] According to the present invention, the auxiliary propulsion provided by the wheel 10 to the hospital bed is achieved by controlling the drive current supplied to the motor 51 based on the measured angular acceleration of the wheel 10. Therefore, Figure 6 It is also shown that a main controller 64 can be arranged on a printed circuit board 55, the main controller being configured to control the drive current supplied to the motor 51 based on the measured angular acceleration of the wheel 10. Figure 5 The diagram illustrates a possible arrangement of the main controller 64 on the printed circuit board 55. It should be noted that in some embodiments, the functionality of the BLDC controller 61 may be integrated into the main controller 64.

[0049] Angular acceleration is continuously determined by a sensor arrangement 65, which includes a rotary encoder (i.e., optical pattern 59 and optical sensor 56) and an acceleration calculation unit 66. In this embodiment, the acceleration calculation unit 66 is integrated into the main controller 64, but acceleration calculation can also be performed in a separate circuit.

[0050] As the optical pattern 59 rotates with the wheel 10, the optical sensor 56 generates a series of pulses, each pulse indicating a position of the wheel. Based on these pulses, the acceleration calculation unit 66 can continuously determine the wheel's current angular velocity and current angular acceleration. For example, the velocity can be determined by counting the number of pulses within a predetermined time window, measuring the time between two consecutive pulses, or using other known algorithms for this purpose. Since acceleration is defined as the change in measured velocity, acceleration can be determined from the velocity. Alternatively, there are various known algorithms that directly determine angular acceleration from the pulses from the optical sensor 56. An example of such algorithms is the use of a correlation matrix or correlation table.

[0051] Since the angular acceleration of wheel 10 is proportional to the linear acceleration of the hospital bed, given the weight of the hospital bed, the angular acceleration is also proportional to the force acting on the hospital bed from the outside (e.g., from a person pushing or pulling the hospital bed). Therefore, at any given moment, the angular acceleration measured in-situ in the wheel serves as a signal that directly indicates the force acting on the hospital bed from the outside, thereby also reflecting the intention of the person pushing or pulling the hospital bed.

[0052] As described above, the auxiliary propulsion provided by the drive wheel 10 to the hospital bed 1 is achieved by controlling the drive current supplied to the motor 51 based on the measured angular acceleration of the wheel. Controlling the drive current is advantageous because the auxiliary torque transmitted to the hospital bed 1 from the motor 51 in the drive wheel is proportional to the drive current supplied to the motor. Therefore, although the hospital bed 1 is driven by the drive wheel, the auxiliary torque used to drive the bed directly depends on the force applied to the bed by the person pushing or pulling it, thus reflecting the person's intention.

[0053] Based on the measured angular acceleration, the current calculation unit 67 can continuously determine the auxiliary current I according to the desired control strategy described below. ass Then, the auxiliary current I can be... ass The requested current I used to drive motor 51 req One control strategy is to only allow the auxiliary current I to... ass It is directly proportional to the measured angular acceleration of the wheel. This control strategy enables rapid and direct control of the motor, but it may also exhibit a degree of "nervousness" as it attempts to follow the irregular walking patterns of the person pushing or pulling the bed.

[0054] exist Figure 7 The diagram illustrates another control strategy to overcome this drawback. This strategy uses two thresholds for the measured angular acceleration of the wheel, namely a positive threshold a. th+ and negative threshold a th- When the measured angular acceleration value is small (i.e., at a...), th- With a th+ When (between), auxiliary current I ass Remain unchanged, such as Figure 7 The values ​​between t0 and t1, t2 and t3, and t4 and t5 are shown. However, when the measured angular acceleration exceeds the positive threshold α... th+ (For example, such as) Figure 7 When the time is between t1 and t2 (as shown), the auxiliary current I ass The linear increase (e.g., at a rate of 5 mA / 10 ms) is related to the angular acceleration exceeding the threshold a. th+ The amplitude is independent. Similarly, when the measured angular acceleration is below the negative threshold a... th- (For example, such as) Figure 7 When the time is between t3 and t4 (as shown), the auxiliary current I ass The linear decrease (e.g., at a rate of -10 mA / 10 ms) is related to the angular acceleration being below the threshold a. th- The amplitude is independent. In this way, very stable control of the motor can be achieved, where irregular walking patterns of people pushing or pulling the hospital bed will not affect the control.

[0055] The control strategy may also include a braking function. If the user (i.e., the person pushing or pulling the hospital bed) initiates a significant deceleration, the auxiliary current I... ass The braking force will decrease rapidly and eventually be generated. Therefore, as an example, if the measured angular acceleration is below the (negative) braking threshold (which is much lower than the aforementioned negative threshold a),... th- Then the auxiliary current I ass Initially, the current will decrease at a relatively low rate, for example, at the rate of -10mA / 10ms mentioned above. Then, the decrease rate can be doubled, for example, every 100ms, until the maximum decrease rate is reached. If the auxiliary current I... ass A value below zero means that braking force will be generated.

[0056] Since the BLDC controller 61 and therefore the motor 51 are controlled by voltage rather than current, a feedback loop is arranged for the drive current. The current detector 68 measures the actual current I drawn by the motor. meas Furthermore, in the motor regulator 69, the actual current I... meas With the determined requested current I reqThe voltage output to the BLDC controller 61 is continuously adjusted and compared to ensure that the actual current I... meas Keep following the requested current I req .

[0057] As described above, although the current calculation unit 67 determines the auxiliary current I based on the measured angular acceleration... ass However, other signals may also affect the determined requested current I. req Therefore, as referenced above... Figure 1 and Figure 2 As mentioned, caster 6 can be locked in a given position (i.e., preventing its rotation), and wheel 10 can be braked or locked (i.e., preventing its rotation within caster 6). These locking mechanisms may include detectors indicating their locked state. Therefore, Figure 8 A wheel lock detector 71 is shown, which provides a signal to the current calculation unit 67 indicating whether the wheel 10 is in a locked state. The current calculation unit 67 can then be configured to provide the output signal I only when the wheel is in an unlocked state. req .same, Figure 8 A slewing lock detector 72 is shown, which provides a signal to the current calculation unit 67 indicating whether the slewing caster 6 is locked. The current calculation unit 67 can then be configured to provide the output signal I only when the slewing caster is locked in the appropriate position (e.g., when the wheel 10 is aligned with the longitudinal axis of the bed 1). req It should be noted that the wheel 10 can be aligned with the longitudinal axis of the bed 1 in two opposite directions. Therefore, the slewing lock detector 72 can also be configured to provide a signal to the current calculation unit 67 indicating the locking direction of the slewing caster 6.

[0058] As described above, the acceleration calculation unit 66 can determine the current angular acceleration and current angular velocity of the wheel 10 based on the pulses received from the optical sensor 56. Therefore, as Figure 8 As shown, the signal indicating the angular velocity of the indicator wheel 10 can also be provided to the current calculation unit 67. Here, the signal can be used, for example, to detect the direction of movement of the bed 1. Thus, a positive velocity can indicate that the swivel caster 6 is moving in the forward direction, while a negative velocity can correspondingly indicate that the swivel caster 6 is moving in the backward direction. The measured velocity may also affect the determination of the auxiliary current I based on the measured angular acceleration. ass In this way. As an example, such as Figure 7 As shown, when the measured angular acceleration exceeds the positive threshold a th+ At that time, the auxiliary current I ass The rate of linear increase can depend on the measured speed; for example, a higher rate of increase can be used for a lower speed.

[0059] Hospital beds are not always placed on or moved on perfectly level surfaces. Instead, they sometimes need to be moved up or down a ramp, which can affect their movement. To take this into account, the swivel caster 6 may also include a tilt detector 75, such as... Figure 9 and Figure 5 As shown, the tilt detector 75 can be disposed on a printed circuit board 55. In one embodiment, the tilt detector 75 includes a three-dimensional accelerometer arranged to measure gravitational acceleration relative to a plane 24 defined by the corners of the rectangular base 2. The accelerometer is a DC-responsive accelerometer, which can be used to measure static acceleration (such as gravitational acceleration).

[0060] Figure 10 The image shows bed 1 placed on a horizontal surface. Therefore, plane 24 is also a horizontal plane. Tilt detector 75 is configured to measure gravitational acceleration along three orthogonal axes (i.e., the X-axis, Y-axis, and Z-axis). The X-axis and Y-axis lie in a plane parallel to plane 24, i.e., in… Figure 10 In the horizontal plane, the X-axis lies in the longitudinal direction of bed 1, while the Z-axis is perpendicular to plane 24. Therefore, in Figure 10 In the case where the bed is placed on or moves on a horizontal surface, the tilt detector 75 will not measure gravitational acceleration along the X-axis or Y-axis, but will measure acceleration g (i.e., gravitational acceleration) along the Z-axis. Since no gravitational acceleration is measured in the longitudinal direction of the bed 1 (i.e., along the X-axis), the movement of the bed is unaffected, and the auxiliary current I determined in the current calculation unit 67 based on the measured angular acceleration is calculated as described above. ass The determined requested current I is used as the reference. req use.

[0061] exist Figure 11 The image shows bed 1 placed on an incline that forms an angle α with respect to a horizontal surface. Therefore, angle α also defines the angle between plane 24 and the horizontal plane. In the tilt detector 75, gravitational acceleration is now measured as the longitudinal acceleration component a along the X-axis. x and the vertical acceleration component a along the Z-axis z The longitudinal component a of gravitational acceleration x The size is equal to a x =g tan(α), and since this component is along the longitudinal direction, it exerts a force on the bed, the direction of which is the same as or opposite to the direction of external forces acting on the bed (e.g., from a person pushing or pulling the bed). Therefore, if the bed is pushed uphill, an additional force is required due to the longitudinal component of gravitational acceleration, while a smaller force is required accordingly when the bed is pushed downhill.

[0062] To compensate for this effect, the current calculation unit 67 is configured to determine the gravity compensation current I. grav The gravity compensation current and the longitudinal acceleration component a measured by the tilt detector 75 x Proportional. It should be noted that when the bed is pushed uphill, that is, when the longitudinal acceleration component a... x When the direction of the force is opposite to the direction of the force pushing the bed, the gravity compensation current I... grav It will have a positive value. Correspondingly, when the longitudinal acceleration component a... x When the direction of the force pushing the bed is the same as the direction of the force pushing the bed, that is, when the bed is pushed downhill, the gravity compensation current will have a negative value. In the current calculation unit 67, the gravity compensation current I... grav It is then applied to the auxiliary current I, which is determined as described above based on the measured angular acceleration. ass The sum of these values ​​is used as the determined requested current I. req Therefore, I req =I ass +I grav In this way, the drive wheel 10 can automatically compensate for the additional force required when the bed moves in the uphill direction and the reduced force required when it moves in the downhill direction.

[0063] Furthermore, in certain situations, if the hospital bed 1 is parked on a slope without being braked, this solution can prevent the hospital bed 1 from sliding on its own, because in this case, the angular acceleration measured by the sensor arrangement 65 consists only of the longitudinal acceleration component a. x Therefore, by appropriately selecting the coefficients, I ass and I grav They can cancel each other out.

[0064] In the above embodiment, the tilt detector 75 uses a three-dimensional accelerometer configured to measure gravitational acceleration along three orthogonal axes (i.e., the X-axis, Y-axis, and Z-axis) to determine the longitudinal acceleration component a along the X-axis. x The longitudinal acceleration component, because it is along the longitudinal direction, is used to determine the gravity compensation current I. grav Alternatively, different types of tilt detectors can be used. For example, an angle measuring device or inclinometer can be used to measure the angle α, and then the angle can be determined based on α. x =g tan(α) determines the longitudinal acceleration component a x .

[0065] Although various embodiments of the invention have been described and illustrated, the invention is not limited thereto, but may be practiced in other ways within the scope of the subject matter defined in the appended claims.

Claims

1. A swivel caster (6), comprising: ● Wheel (10) ● Electric motor (51), the electric motor (51) being contained in the hub (33) to drive the wheel (10), and ● Shaft (26), the shaft (26) is used to connect the swivel caster (6) to a movable wheel device and to enable the swivel caster (6) to rotate about the longitudinal axis (27) of the shaft (26). The slewing caster (6) is characterized in that it further comprises: ● Sensor arrangement (65), the sensor arrangement (65) including a rotary encoder arranged in the wheel hub (33) and configured to measure the angular acceleration of the wheel (10), and ● Controller (64), which is configured to control the drive current supplied to the motor (51) based on the measured angular acceleration.

2. The swivel caster according to claim 1, characterized in that, The swivel caster (6) includes a slip ring (41) configured to establish an electrical connection with a movable wheel device.

3. The slewing caster according to claim 1 or 2, characterized in that, The controller (64) is configured to control the drive current supplied to the motor (51) in the following manner: ●When the measured angular acceleration exceeds the positive threshold (a th+ When ), increase the drive current supplied to the motor (51), ●When the measured angular acceleration is below the negative threshold (a th- When ), reduce the drive current supplied to the motor (51), and ●When the measured angular acceleration is within the negative threshold (a th- ) and the positive threshold (a) th+ When the current is between 5 and 6, the drive current supplied to the motor (51) remains constant.

4. The slewing caster according to any one of claims 1 to 3, characterized in that, The slewing caster (6) includes a slewing lock, which is configured in a locked position to prevent the slewing caster (6) from rotating, and wherein the controller (64) is configured to drive the motor (51) only when the slewing lock is in its locked position.

5. The slewing caster according to any one of claims 1 to 4, characterized in that, The swivel caster (6) includes a brake that is configured in a braking position to prevent the wheel (10) from rotating, and wherein the controller (64) is configured to drive the motor (51) only when the brake is not in its braking position.

6. The slewing caster according to any one of claims 1 to 5, characterized in that, The sensor arrangement (65) is further configured to measure the angular velocity of the wheel (10), and the controller (64) is further configured to drive the motor (51) according to the measured angular velocity.

7. The slewing caster according to any one of claims 1 to 6, characterized in that, ●The swivel caster (6) further includes a tilt detector (75), which is arranged to determine the component of gravitational acceleration in the driving direction of the wheel (10) (a x ),and ●The controller (64) is further configured to adjust according to the determined component of gravitational acceleration (a x ) The electric motor (51) drives the drive wheel (10).

8. The slewing caster according to claim 7, characterized in that, The controller (64) is configured to adjust according to the determined component of gravitational acceleration (a x Determine the tilt compensation current (I) grav ), and uses a drive current (I) determined based on the measured angular acceleration. ass Combined with the tilt compensation current (I) grav The electric motor (51) drives the wheel (10).

9. The slewing caster according to claim 7 or 8, characterized in that, The tilt detector (75) includes a three-dimensional DC-response accelerometer arranged to measure gravitational acceleration relative to a plane perpendicular to the longitudinal axis (27) of the shaft (26), the shaft (26) being used to connect the swivel caster (6) to a movable wheeled device.

10. The slewing caster according to claim 7 or 8, characterized in that, The tilt detector (75) includes an angle measuring device arranged to determine an angle (α), which is the angle between the plane perpendicular to the longitudinal axis (27) of the shaft (26) for connecting the swivel caster (6) to the movable wheel device and the horizontal plane, and the controller (64) is further configured to determine the component of the gravitational acceleration (α) based on the determined angle (α). x ).

11. A movable wheeled device, said movable wheeled device comprising at least one swivel caster according to any one of claims 1 to 10.

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