Wheeled carriage having a powered auxiliary wheel, auxiliary wheel overtravel, and an auxiliary wheel drive and control system

• US 6,752,224 B2
• Filed: 02/28/2002
• Issued: 06/22/2004
• Est. Priority Date: 02/28/2002
• Status: Expired due to Term

• Current Assignee: Stryker Corporation
• Original Assignee: Stryker Corporation
• Inventors: Hopper, Christopher J., Hayes, Michael Joseph, Gentile, Christopher, McDaniel, Richard L., Newsome, Randy, Bartow, Richard Jay, Beyer, Patrick
• Primary Examiner(s): Morris, Lesley D.
• Assistant Examiner(s): Lum, L.
• Application Number:
  US10/086,012
• Publication Number:
  US 20030159861A1
• Time in Patent Office: 845 Days
• Field of Search: 5 8/61, 560/0, 180/65.1, 180/65.5, 180/11, 180/19-- 1, 180/22-24, 280/250.1, 280/304.1
• US Class Current: 180/22
• CPC Class Codes: A61G 1/0218 3 pairs having wheels within a pair on the same position in longitudinal direction, e.g. on the same axis
• CPC Class Codes: A61G 1/0237 having at least one swivelling wheel, e.g. castors
• CPC Class Codes: A61G 1/0268 having deployable or retractable wheels
• CPC Class Codes: A61G 1/0275 having driven wheels, e.g. motorised
• CPC Class Codes: A61G 1/0287 having brakes, e.g. slowing down and/or holding details of brake actuators on castors B60B33/0078; brakes on hand carts B62B5/04; brakes in general F16D49/00 - F16D65/853
• CPC Class Codes: A61G 1/042 Suspension means
• CPC Class Codes: A61G 2203/36 for motion
• CPC Class Codes: A61G 7/0528 Steering or braking devices for castor wheels
• CPC Class Codes: A61G 7/08 Apparatus for transporting beds
• CPC Class Codes: B60L 2200/34 Wheel chairs

Abstract

A wheeled carriage for supporting a patient in a substantially horizontal position includes a patient support having head and foot ends and a wheeled base supported by castered wheels. Auxiliary wheels are suspendably mounted on a wheel support structure with the axis of the auxiliary wheels spaced from a midpoint of the wheeled base. A control apparatus controls the wheel support structure to move the auxiliary wheels between a first deployed position whereat castered wheels at one end of the carriage are elevated from a floor surface, and a second stored position with the auxiliary wheels out of engagement with the floor surface. The wheeled carriage includes a drive motor for powering the auxiliary wheels. A drive member applies force to a load cell on the wheeled carriage. The load cell outputs a drive signal to drive the auxiliary wheels. An auxiliary wheel drive and control system accelerates or decelerates the carriage by comparing the drive signal with a threshold value that changes dependent on the velocity of the carriage.

Claims

1. A wheeled carriage for supporting a patient in a substantially horizontal position, comprising:

a patient support having a length, opposing ends of the length comprising a head end and a foot end of said patient support, said patient support having a pair of lateral sides intermediate the head and foot ends;

a wheeled base having a length and supporting said patient support and enabling movement of said patient support, said wheeled base including at least four floor surface engaging wheels spaced from one another, said wheeled carriage having a first edge corresponding to the head end of said patient support and a second edge corresponding to the foot end of said patient support, said wheeled base having an imaginary transverse centerline located at a midpoint of the length of said wheeled base and dividing said wheeled base;

an auxiliary wheel support structure secured to said wheeled base and suspendedly supporting at least one auxiliary wheel at an axis thereof to said wheeled base, wherein the axis of said at least one auxiliary wheel is spaced from the centerline at the midpoint of said wheeled base toward the second edge of said wheeled base, said auxiliary wheel support structure including a pair of spaced parallel frame members secured at first ends to said wheeled base and secured at second ends to a cross bar, said cross bar supporting a support member including a cam follower and a roller member; and

a control apparatus for controlling said auxiliary wheel support structure to move said at least one auxiliary wheel between a first deployed position whereat said at least one auxiliary wheel is engaged with a floor surface and a second stored position whereat said auxiliary wheel is out of engagement with the floor surface,

wherein, when a portion of the floor surface has a lower depth directly below said deployed auxiliary wheel such that the four surface engaging wheels engage the floor surface, said auxiliary wheel support structure enables downward movement of said at least one auxiliary wheel from said deployed position so that said auxiliary wheel maintains contact with the floor surface.

2. The wheeled carriage of claim 1, wherein said at least one auxiliary wheel is uncastered and has a height greater than the height of said floor engaging wheels and a width greater than the width of said floor engaging wheels.

3. The wheeled carriage of claim 1, wherein said at least one auxiliary wheel comprises first and second parallel aligned auxiliary wheels having the same axis of rotation.

4. The wheeled carriage of claim 1, wherein said control apparatus comprises a rotatable shaft for rotation by a user and a cam apparatus responsive to the rotation.

5. The wheeled carriage of claim 4, wherein said cam apparatus further comprises an elongate crank arm fixed at one end to said rotatable shaft and pivotably secured at a second end to a first end of an elongate cam linkage member, a second end of said cam linkage member being pivotably connected to a cam.

6. The wheeled carriage of claim 5, wherein said cam coacts with said cam follower to move said at least one auxiliary wheel between the first deployed position and the second stored position.

7. The wheeled carriage of claim 1, wherein said auxiliary wheel support structure supports a motor for selectively driving said auxiliary wheel.

8. The wheeled carriage of claim 1, wherein said auxiliary wheel support structure includes a linkage element pivotally secured to said wheeled base, said linkage element at a first end having an opening receiving said roller member.

9. The wheeled carriage of claim 8, wherein said auxiliary wheel support structure includes a push rod pivotally secured at a first end to said wheeled base and pivotally and slidably secured at a second end to said linkage element.

10. The wheeled carriage of claim 9, said auxiliary wheel support structure including a rod spring mounted about and along the length of said push rod for applying a biasing force at ends thereof,

wherein, when said deployed auxiliary wheel is positioned at the portion of the floor surface such that the four surface engaging wheels engage the floor surface, said rod spring applies a biasing force through said linkage element and said roller member to move said auxiliary wheel downwardly to maintain contact with the floor surface.

11. The wheeled carriage of claim 9, said push rod including a rod slot at the second end thereof and a cross pin extending through the rod slot and secured to said linkage element to enable pivoting of said rod and said linkage element, and

wherein the rod slot enables said linkage element to move toward said rod when the lengths of said rod and said linkage element are substantially in alignment with each other, so that said rod and said linkage element are capable of pivoting to an upright position or a downward position.

12. A wheeled carriage for supporting a patient in a substantially horizontal position, comprising:

a patient support having a length, opposing ends of the length comprising a head end and a foot end of said patient support, said patient support having a pair of lateral sides intermediate the head and foot ends;

a wheeled base having a length and supporting said patient support and enabling movement of said patient support, said wheeled base including at least four floor surface engaging wheels spaced from one another, said wheeled carriage having a first edge corresponding to the head end of said patient support and a second edge corresponding to the foot end of said patient support, said wheeled base having an imaginary transverse centerline located at a midpoint of the length of said wheeled base and dividing said wheeled base;

an auxiliary wheel support structure secured to said wheeled base and suspendedly supporting at least one auxiliary wheel at an axis thereof to said wheeled base, wherein the axis of said at least one auxiliary wheel is spaced from the centerline at the midpoint of said wheeled base toward the second edge of said wheeled base, said auxiliary wheel support structure including a floating frame; and

a control apparatus for controlling said auxiliary wheel support structure to move said at least one auxiliary wheel between a first deployed position whereat said auxiliary wheel is engaged with a floor surface and a second stored position whereat said auxiliary wheel is out of engagement with the floor surface,

wherein, when a portion of the floor surface has a lower depth directly below said at least one deployed auxiliary wheel such that the four surface engaging wheels engage the floor surface, said floating frame of said auxiliary wheel support structure moves downwardly along with said at least one auxiliary wheel mounted thereto to maintain said at least one auxiliary wheel in contact with the lowered floor surface.

24. The wheeled carriage of claim 12, including a motor mounted to said floating frame for driving said auxiliary wheel, and wherein, when the portion of the floor surface having the lower depth is directly below said deployed auxiliary wheel such that the four surface engaging wheels engage the floor surface, said floating frame has a predetermined weight and pivots the auxiliary wheel downwardly, such that said at least one auxiliary wheel maintains sufficient contact to retain drive traction at the lowered floor surface.

13. A wheeled carriage for supporting a patient in a substantially horizontal position, comprising:

a patient support having a length, opposing ends of the length comprising a head end and a foot end of said patient support, said patient support having a pair of lateral sides intermediate the head and foot ends;

a wheeled base having a length and supporting said patient support and enabling movement of said patient support, said wheeled base including at least four floor surface engaging wheels spaced from one another, said wheeled carriage having a first edge corresponding to the head end of said patient support and a second edge corresponding to the foot end of said patient support, said wheeled base having an imaginary transverse centerline located at a midpoint of the length of said wheeled base and dividing said wheeled base;

an auxiliary wheel support structure secured to said wheeled base and suspendedly supporting at least one auxiliary wheel at an axis thereof to said wheeled base, wherein the axis of said at least one auxiliary wheel is spaced from the centerline at the midpoint of said wheeled base toward the second edge of said wheeled base, said auxiliary wheel support structure including a loading frame pivotally mounted to said wheeled base and a floating frame mounted to said loading frame; and

a control apparatus for controlling said auxiliary wheel support structure to move said at least one auxiliary wheel between a first deployed position whereat said auxiliary wheel is engaged with a floor surface and a second stored position whereat said auxiliary wheel is out of engagement with the floor surface,

wherein, when a portion of the floor surface has a lower depth directly below said at least one deployed auxiliary wheel such that the four surface engaging wheels engage the floor surface, said floating frame of said auxiliary wheel support structure moves downwardly along with said at least one auxiliary wheel mounted thereto to maintain said at least one auxiliary wheel in contact with the lowered floor surface.

14. The wheeled carriage of claim 13, wherein said loading frame pivotally supports said floating frame.

15. The wheeled carriage of claim 14, wherein said floating frame is unbiased to enable pivoting movement in an upward or downward direction.

16. The wheeled carriage of claim 14, wherein said at least one auxiliary wheel comprises first and second parallel aligned auxiliary wheels supported by a single auxiliary wheel axle, said axle secured to said floating frame.

17. The wheeled carriage of claim 16, wherein said loading frame comprises two frame members secured at first ends to said wheeled base and secured at second ends to a cross bar.

18. The wheeled carriage of claim 17, wherein said loading frame includes a cam follower mounted to said cross bar and first and second slotted elements mounted to said two frame members adjacent the second ends thereof, each slotted element having a vertical slot.

19. The wheeled carriage of claim 18, wherein said auxiliary wheel axle secured to said floating frame extends through said vertical slots, said auxiliary wheels being mounted at the ends of said auxiliary wheel axle outwardly from said slotted elements.

20. The wheeled carriage of claim 17, wherein said floating frame includes first and second beams pivotally secured at respective first ends to said first and second frame members of said loading frame, said first and second beams supporting a plate element therebetween.

21. The wheeled carriage of claim 20, wherein said first and second beams have apertures aligned parallel to the imaginary transverse centerline, said apertures enabling passage of said auxiliary wheel axle therethrough, said auxiliary wheel axle being rotatably mounted to said floating frame.

22. The wheeled carriage of claim 18, wherein said control apparatus comprises a cam apparatus and at least one spring for biasing said loading frame to a raised position so that said auxiliary wheels move to the stored position with said auxiliary wheel axle resting at a lower portion of the vertical slots.

23. The wheeled carriage of claim 22, wherein said control apparatus controls said cam apparatus to coact with said cam follower to lower said loading frame to a position corresponding to the deployed position with said auxiliary wheel axle positioned at an upper end of the vertical slots.

25. A power assisted wheeled carriage for supporting a patient in a substantially horizontal position, comprising:

a patient support having a length, opposing ends of the length comprising a head end and a foot end of said patient support, said patient support having a pair of lateral sides intermediate the head and foot ends;

a wheeled base having a length and supporting said patient support and enabling movement of said patient support, said wheeled base including at least four floor surface engaging wheels spaced from one another, said wheeled carriage having a first edge corresponding to the head end of said patient support and a second edge corresponding to the foot end of said patient support;

an auxiliary wheel support structure secured to said wheeled base and suspendedly supporting at least one auxiliary wheel about an axis transverse to the length of said wheeled base;

a control apparatus for controlling said auxiliary wheel support structure to move said at least one auxiliary wheel between a first deployed position in contact with a floor surface, and a second stored position whereat said at least one auxiliary wheel is out of engagement with the floor surface;

an auxiliary wheel drive power circuit for driving said at least one auxiliary wheel;

a processor for controlling the auxiliary wheel drive power circuit to control acceleration, deceleration, velocity and direction of driving of said at least one auxiliary wheel;

a drive member at an end of said wheeled carriage for receiving a force input from a user in one of first and second opposing directions; and

a load cell for measuring the force input applied to said drive member, and providing an output to said processor,

wherein said processor controls driving of said at least one auxiliary wheel in response to the force input and the direction of the force input applied to said drive member.

26. The power assisted wheeled carriage of claim 25, wherein, when the deployed auxiliary wheel engages a floor surface, two of said floor engaging wheels adjacent said foot end of said wheeled carriage are elevated away from the floor surface.

27. The power assisted wheeled carriage of claim 25, wherein said drive member comprises a handle.

28. The power assisted wheeled carriage of claim 26, wherein, when a portion of the floor surface has a lower depth directly below said at least one deployed auxiliary wheel such that the four surface engaging wheels engage the floor surface, said auxiliary wheel support structure enables downward movement of said at least one auxiliary wheel from said deployed position so that said auxiliary wheel maintains contact with the floor surface.

29. The power assisted wheeled carriage of claim 25, wherein said wheeled base has an imaginary transverse centerline located at a midpoint of the length of said wheeled base and dividing said wheeled base, and wherein the axis of said at least one auxiliary wheel is spaced from the centerline at the midpoint of said wheeled base toward the second edge of said wheeled base.

30. The power assisted wheeled carriage of claim 25, including a force transfer element for transferring force applied to said drive member to said load cell.

31. The power assisted wheeled carriage of claim 25, wherein said drive member effectively remains stationary during application of the force to said load cell.

32. The power assisted wheeled carriage of claim 25, wherein the output from said load cell comprises a drive signal value, and said processor compares the drive signal value with a drive signal threshold value, and does not change the velocity of said wheeled carriage when the drive signal value is less than the drive signal threshold value.

33. A power assisted wheeled carriage for supporting and transporting a person in a substantially horizontal position, comprising:

a patient support having a length, opposing ends of the length comprising a head end and a foot end of said patient support;

a wheeled base having a length and supporting said patient support and enabling movement of said patient support, said wheeled base including at least four floor surface engaging wheels spaced from one another, said wheeled carriage having a first edge corresponding to the head end of said patient support and a second edge corresponding to the foot end of said patient support;

an auxiliary wheel support structure secured to said wheeled base and for supporting at least one auxiliary wheel about an axis transverse to the length of said wheeled base, and moving said at least one auxiliary wheel into a first deployed position contacting the floor and a second stored position out of engagement with the floor;

a drive motor for driving said auxiliary wheel;

a power drive control circuit for controlling said drive motor;

a drive member mounted on the wheeled carriage for providing a drive signal in one of a first direction and a second opposing direction;

a drive and control system for receiving the drive signal and for driving said at least one auxiliary wheel by providing a power signal to said power drive control circuit; and

a drive motor disconnect arrangement for open circuiting said drive motor from said power drive control circuit to enable manually powered movement of said wheeled carriage, said drive motor disconnect arrangement including first and second disconnect elements for disconnecting said drive motor from said power drive control circuit and from a parallel circuit.

34. The power assisted wheeled carriage of claim 33, wherein said drive motor disconnect arrangement includes a manual actuator for manually actuating said first and second disconnect elements.

35. The power assisted wheeled carriage of claim 33, wherein said parallel circuit includes a motor disable relay.

36. A power assisted wheeled carriage for supporting and transporting a person in a substantially horizontal position, comprising:

a patient support having a length, opposing ends of the length comprising a head end and a foot end of said patient support;

a wheeled base having a length and supporting said patient support and enabling movement of said patient support;

an auxiliary wheel support structure secured to said wheeled base and suspendedly supporting at least one auxiliary wheel at an axis thereof to said wheeled base;

a control apparatus for controlling said auxiliary wheel support structure to move said at least one auxiliary wheel between a first deployed position whereat said auxiliary wheel is engaged with a floor surface and a second stored position whereat said auxiliary wheel is out of engagement with the floor surface;

a drive motor for driving said auxiliary wheel;

a power drive control circuit for controlling said drive motor;

a drive member for receiving an input from a user in one of a first direction and a second opposing direction;

an input measuring device for measuring the input from the drive member and providing a drive signal;

a drive and control system for receiving the drive signal from said input measuring device, said drive and control system comparing the value of the drive signal with a drive signal threshold value, and providing a power signal to said power drive control circuit for driving said at least one auxiliary wheel in response to the value of the drive signal and the direction of the drive signal when the drive signal value exceeds the drive signal threshold value.

37. The power assisted wheeled carriage of claim 36, wherein the input from a user comprises a force input and said input measuring device comprises a force measuring device.

38. The power assisted wheeled carriage of claim 37, wherein said force measuring device comprises a load cell.

39. The power assisted wheeled carriage of claim 36, wherein said drive member remains essentially stationary when applying the input to the input measuring device.

40. The power assisted wheeled carriage of claim 36, wherein said drive and control system varies the drive signal threshold value in response to the velocity of the vehicle.

41. The power assisted wheeled carriage of claim 40, wherein the drive signal threshold value increases at increasing velocities of the carriage.

42. The power assisted wheeled carriage of claim 36, wherein, when the wheeled carriage is traveling in a first direction and the drive signal is in the first direction, said drive and control system accelerates the wheeled carriage.

43. The power assisted wheeled carriage of claim 42, wherein, when the wheeled carriage is traveling in a first direction and the drive signal is in the second opposing direction, said drive and control system decelerates the wheeled carriage.

44. The power assisted wheeled carriage of claim 43, wherein, when the wheeled carriage is traveling in a first direction and the drive signal is in the second opposing direction for an extended time period, said drive and control system decelerates the wheeled carriage moving in the first direction, stops the wheeled carriage, and accelerates the wheeled carriage in the second opposing direction.

45. The power assisted wheeled carriage of claim 36, wherein the drive motor comprises a DC electric motor, and the power signal comprises electric pulses having a calculated width supplied to the DC electric motor.

46. The power assisted wheeled carriage of claim 36, including four castered wheels, with one of said castered wheels mounted at each opposing corner at each opposing end of said wheeled base.

47. The power assisted wheeled carriage of claim 36, wherein said wheeled base includes at least four floor surface engaging wheels spaced from one another, and said wheeled carriage has a first edge corresponding to the head end of said patient support and a second edge corresponding to the foot end of said patient support, and said wheeled base having an imaginary transverse centerline located at a midpoint of the length of said wheeled base and dividing said wheeled base, and wherein the axis of said at least one auxiliary wheel is spaced from the centerline at the midpoint of said wheeled base toward the second edge of said wheeled base.

48. The power assisted wheeled carriage of claim 47, wherein at the first deployed position, when said auxiliary wheel engages the floor surface, two of said floor surface engaging wheels adjacent said foot end of said wheeled carriage are elevated away from and out of contact with the floor surface when the floor surface is even.

49. The power assisted wheeled carriage of claim 36, wherein the drive and control system provides a ramping effect for the wheeled carriage.

50. A method for driving a power assisted wheeled carriage used for supporting and transporting a person in a substantially horizontal position, the carriage including a patient support having a length, opposing ends of the length comprising a head end and a foot end of said patient support, a wheeled base having a length and supporting said patient support and enabling movement of said patient support, an auxiliary wheel support structure secured to said wheeled base and for biasing at least one auxiliary wheel into a first position contacting the floor and a second raised position out of engagement with the floor, and a drive motor for driving said at least one auxiliary wheel, the method including the steps of:

(a) sensing the presence of a force input by an operator to a drive member for controlling driving of said at least one auxiliary wheel in a first direction, and when the force input is absent, maintaining the velocity of said at least one auxiliary wheel and returning to a main program; and

(b) measuring magnitude of the force input and direction of the force input applied by the operator, and

(i) when the direction of the force input is in the direction as previously sensed, sensing if the velocity is at a maximum velocity, and (1) maintaining the velocity of the wheeled carriage when the velocity is at a maximum value, and (2) when the velocity is not at a maximum value, using the magnitude of the force input to determine an acceleration rate;

(ii) when the direction of the force input is not in the direction as previously sensed, sensing if the velocity is at zero velocity, and (1) when the velocity of the wheeled carriage is at zero, using the force input to determine an acceleration rate in the direction of the force applied by the operator, and (2) when the velocity is not at zero, using the force to determine a deceleration rate.

51. The method for driving a power assisted wheeled carriage of claim 50, wherein the step of sensing the presence or absence of the force input is calculated by comparing a value of the measured force with a force threshold value.

52. The method for driving a power assisted wheeled carriage of claim 51, wherein the force threshold value increases when the velocity of the auxiliary wheel increases.

53. The method for driving a power assisted wheeled carriage of claim 50, including a drive member for receiving the force input from the operator.

54. The method for driving a power assisted wheeled carriage of claim 53, wherein the step of measuring the force input includes a load cell secured to said drive member, the load cell sensing the force input applied to the drive member.

55. The method for driving a power assisted wheeled carriage of claim 50, including the steps of:

sensing presence of an operator'"'"'s hand on the drive member, and

executing a controlled stop of the wheeled carriage when the operator'"'"'s hand is not on the drive member.

56. The method for driving a power assisted wheeled carriage of claim 50, including the step of applying a power signal to the drive motor to control and drive the wheeled carriage at the determined acceleration or deceleration rate.

57. The method for driving a power assisted wheeled carriage of claim 53, including determining essentially no change in the force input for a predetermined time period indicating an operator release of the drive member, wherein, in response to the essentially no change in the force input during the time period, the drive and control system stops movement of the wheeled carriage.

58. A power assisted wheeled carriage for supporting and transporting a person in a substantially horizontal position, comprising:

a patient support having a length, opposing ends of the length comprising a head end and a foot end of said patient support;

a wheeled base having a length and supporting said patient support and enabling movement of said patient support, said wheeled base including at least four floor surface engaging wheels spaced from one another, said wheeled carriage having a first edge corresponding to the head end of said patient support and a second edge corresponding to the foot end of said patient support;

an auxiliary wheel support structure secured to said wheeled base and for supporting at least one auxiliary wheel about an axis transverse to the length of said wheeled base, and moving said at least one auxiliary wheel into a first deployed position contacting the floor and a second stored position out of engagement with the floor;

a drive motor for driving said auxiliary wheel;

a power drive control circuit for controlling said drive motor;

a drive member mounted on the wheeled carriage for providing a drive signal in one of a first direction and a second opposing direction;

a drive and control system for receiving the drive signal and for driving said at least one auxiliary wheel by providing a power signal to said power drive control circuit; and

a drive motor disabling device for providing a parallel electrical connection across said drive motor to prevent a voltage improperly applied to said drive motor from powering said drive motor and to resist or slow uncontrolled movement of said wheeled carriage.

59. The power assisted wheeled carriage of claim 58, wherein said drive motor disabling device comprises a motor disable relay.

60. A power assisted wheeled carriage for supporting and transporting a person in a substantially horizontal position, comprising:

a patient support having a length, opposing ends of the length comprising a head end and a foot end of said patient support;

a wheeled base having a length and supporting said patient support and enabling movement of said patient support, said wheeled base including at least four floor surface engaging wheels spaced from one another, said wheeled carriage having a first edge corresponding to the head end of said patient support and a second edge corresponding to the foot end of said patient support;

an auxiliary wheel support structure secured to said wheeled base and for supporting at least one auxiliary wheel about an axis transverse to the length of said wheeled base, and moving said at least one auxiliary wheel into a first deployed position contacting the floor and a second stored position out of engagement with the floor;

a drive motor for driving said auxiliary wheel;

a power drive control circuit for controlling said drive motor;

a drive member mounted on the wheeled carriage for providing a drive signal in one of a first direction and a second opposing direction;

a drive and control system for receiving the drive signal and for driving said at least one auxiliary wheel by providing a power signal to said power drive control circuit; and

a voltage system sensor unit for sensing a change in system voltage over a predetermined time and calculating a measured voltage change value,

wherein said drive and control system, compares said measured voltage change value with a predetermined value, and when said measured value is greater than the predetermined value, said drive and control system changes the power signal to said power drive control circuit to maintain the velocity of said wheeled carriage at a constant velocity.

61. The power assisted wheeled carriage of claim 60, wherein said voltage system sensor unit comprises a drive motor voltage sensor unit for sensing change in voltage across the drive motor caused by an increase or decrease in an electrical load to said motor.

62. The power assisted wheeled carriage of claim 61, wherein driving of said wheeled carriage from a smooth surface onto a rough surface increases resistance or resistive force applied to said drive motor through said at least one auxiliary wheel, increases the electrical load to said motor, while simultaneously decreasing voltage across said drive motor.

63. A wheeled carriage for supporting a patient in a substantially horizontal position, comprising:

a patient support having a length, opposing ends of the length comprising a head end and a foot end of said patient support, said patient support having a pair of lateral sides intermediate the head and foot ends;

a wheeled base having a length and supporting said patient support and enabling movement of said patient support, said wheeled base including at least four floor surface engaging wheels spaced from one another, said wheeled carriage having a first edge corresponding to the head end of said patient support and a second edge corresponding to the foot end of said patient support, said wheeled base having an imaginary transverse centerline located at a midpoint of the length of said wheeled base and dividing said wheeled base;

an auxiliary wheel support structure secured to said wheeled base and suspendedly supporting at least one auxiliary wheel at an axis thereof to said wheeled base, wherein the axis of said at least one auxiliary wheel is spaced from the centerline at the midpoint of said wheeled base toward the second edge of said wheeled base; and

a control apparatus for controlling said auxiliary wheel support structure to move said at least one auxiliary wheel between a first deployed position whereat said auxiliary wheel is engaged with a floor surface and two of said floor engaging wheels adjacent said foot end of said wheeled carriage are elevated away from the floor surface when the floor surface is even, and a second stored position whereat said at least one auxiliary wheel is out of engagement with the floor surface; and

a retraction damper unit for slowing movement of said at least one auxiliary wheel from the deployed position toward the stored position to decrease a force caused when the two of said floor engaging wheels adjacent said foot end of said wheeled carriage contact the floor surface during raising of said at least one auxiliary wheel.

64. The wheeled carriage according to claim 63, said control apparatus including a rotatable shaft oriented on an axis parallel to a longitudinal axis of said rectangular patient support and having a first manually manipulatable member connected to said rotatable shaft, said first manually manipulatable member being oriented adjacent at least one of said head and foot ends.

65. The wheeled carriage according to claim 64, said wheeled carriage further comprising a cam apparatus including a linkage unit pivotally securing said rotary shaft of said control apparatus to a cam, and a cam follower secured to said auxiliary wheel support structure, said cam follower being movable by said cam, wherein rotation of said cam operates on said cam follower so that said at least one auxiliary wheel moves between the first deployed position and the second stored position.

66. The wheeled carriage according to claim 65, wherein said retraction damper unit includes a damper for resisting movement of said cam from a cam position corresponding to the first deployed position of said at least one auxiliary wheel to a cam position corresponding to the stored position of said at least one auxiliary wheel.

67. The wheeled carriage according to claim 66 wherein said retraction damper unit includes a damper roller for contacting an outwardly projecting cam surface of said cam, and a linkage unit linking said damper roller to said damper.

68. The wheeled carriage according to claim 67, wherein said damper resists movement of said damping rod only in one of said first and second opposing directions corresponding to retracting of said at least one auxiliary wheel.

69. The wheeled carriage according to claim 63, wherein said retraction damper unit includes a damping rod within a damper, said damping rod being movable in first and second opposing directions.

70. A wheeled carriage for supporting a patient in a substantially horizontal position, comprising:

a patient support having a length, opposing ends of the length comprising a head end and a foot end of said patient support, said patient support having a pair of lateral sides intermediate the head and foot ends;

a wheeled base having a length and supporting said patient support and enabling movement of said patient support, said wheeled base including at least four floor surface engaging wheels spaced from one another, said wheeled carriage having a first edge corresponding to the head end of said patient support and a second edge corresponding to the foot end of said patient support, said wheeled base including first and second spaced elongate frame members extending the length of said wheeled base;

an auxiliary wheel support structure secured to said wheeled base and suspendedly supporting at least one auxiliary wheel at an axis thereof to said wheeled base, wherein the axis of said at least one auxiliary wheel is spaced from the centerline at a midpoint of said wheeled base toward the second edge of said wheeled base, said auxiliary wheel support structure comprising;

a push rod pivotally secured at a first end to said wheeled base; and

a linkage element having a first end movable when said auxiliary wheel support structure is moved between a first deployed position whereat said auxiliary wheel is engaged with a floor surface and a second stored position whereat said auxiliary wheel is out of engagement with the floor surface, a second end of said push rod being pivotally secured to a second end of said linkage element; and

a control apparatus for coacting with the first end of said linkage element to move said at least one auxiliary wheel between the first deployed position and the second stored position,

wherein, when a portion of the floor surface has a lower depth directly below said deployed auxiliary wheel such that the four surface engaging wheels engage the floor surface, said auxiliary wheel support structure enables downward movement of said at least one auxiliary wheel from said deployed position so that said auxiliary wheel maintains contact with the floor surface, and

wherein the second ends of said linkage element and said push rod are at a raised position relative to said frame members when said auxiliary wheel is in the deployed position and the second ends of said linkage element and said push rod are at a lowered position relative to said frame members when said auxiliary wheel is in the second stored position.

71. The wheeled carriage of claim 70, wherein the first end of said linkage element includes an opening receiving a roller member.

72. The wheeled carriage of claim 71, wherein said auxiliary wheel support structure includes a cam follower and said control apparatus comprises a rotatable shaft for rotation by a user and a cam apparatus responsive to the rotation, and

wherein said cam apparatus coacts with said cam follower and said roller member to simultaneously pivot the first end of said linkage element and the second end of said linkage element, thus moving the second end of said push rod and said linkage element between the raised position and the lowered position relative to said wheeled base.

73. The wheeled carriage of claim 70, wherein the second end of said push rod is pivotally and slidably secured to the second end of said linkage element.

74. The wheeled carriage of claim 73, said push rod including a rod slot at the second end thereof and a cross pin extending through the rod slot and secured to the second end of said linkage element, wherein the rod slot enables said linkage element to move toward said rod when the lengths of said rod and said linkage element are substantially in alignment with each other.

75. The wheeled carriage of claim 73, said auxiliary wheel support structure including a rod spring mounted about and along the length of said rod member for applying a biasing force at ends thereof,

wherein, when said deployed auxiliary wheel is positioned at the portion of the floor surface such that the four surface engaging wheels engage the floor surface, said rod spring applies a biasing force through said linkage element and said roller member to move said auxiliary wheel downwardly to maintain contact with the floor surface.

76. The wheeled carriage of claim 73, wherein said auxiliary wheel support structure includes a pair of spaced parallel auxiliary wheel support frame members pivotally secured at first ends to said wheeled base and secured at second ends to a cross bar, said cross bar supporting a support member including a cam follower, and a roller member received in an opening at the first end of said linkage element.

77. The wheeled carriage of claim 76, wherein said control apparatus comprises a rotatable shaft for rotation by a user and a cam apparatus responsive to the rotation,

wherein said cam apparatus coacts with said cam follower and said roller member to simultaneously pivot the first end of said linkage element and the second end of said linkage element.

78. The wheeled carriage of claim 70, wherein said control apparatus comprises a cam apparatus and said auxiliary wheel support structure includes a cam follower and a support member, said cam apparatus coacting with said cam follower and a roller member located at the first end of said linkage element.