Patient transport apparatus with controllable auxiliary wheel assembly

1. A patient transport apparatus for transporting a patient over a surface, said patient transport apparatus comprising:

a base;

support wheels coupled to said base and swivelable about swivel axes;

an auxiliary wheel assembly coupled to said base and comprising an auxiliary wheel configured to move between a stowed position spaced from the surface and deployed positions in contact with the surface, said auxiliary wheel assembly further comprising an actuator operably coupled to said auxiliary wheel to move said auxiliary wheel between said stowed position and said deployed positions;

a sensing system; and

a controller coupled to said sensing system to acquire a measurement associated with a current load applied to said auxiliary wheel, said controller configured to generate a control signal based on comparing said measurement to a predetermined value associated with a desired load, and to apply said control signal to said actuator thereby adjusting said current load relative to said desired load; and

wherein said controller is configured to acquire measurements associated with current loads applied to said auxiliary wheel over time and to generate said control signal based on minimizing deviation between said measurements and said predetermined value.

2. The patient transport apparatus of claim 1 , wherein said sensing system comprises a patient weight sensor coupled to said controller to acquire a weight measurement separate from said measurement associated with said current load applied to said auxiliary wheel, said controller configured to determine said predetermined value associated with said desired load based on said weight measurement.

3. The patient transport apparatus of claim 1 , wherein said sensing system comprises a load sensor coupled to said controller to acquire said measurement, said measurement comprising a load value relating to said current load.

4. The patient transport apparatus of claim 1 , wherein said sensing system comprises a displacement sensor coupled to said controller to acquire said measurement, said measurement comprising a displacement value relating to displacement of said actuator.

5. The patient transport apparatus of claim 1 , wherein said sensing system comprises an electrical current sensor coupled to said controller to acquire said measurement, said measurement comprising an electrical current value relating to electrical current utilized by said actuator.

6. The patient transport apparatus of claim 1 , wherein said auxiliary wheel assembly further comprises a drive system to rotate said auxiliary wheel.

7. The patient transport apparatus of claim 1 , wherein said auxiliary wheel assembly further comprises a second auxiliary wheel, each of said auxiliary wheels being rotatably coupled to said base and non-swivelable relative to said base.

8. The patient transport apparatus of claim 7 , wherein said auxiliary wheel assembly further comprises a second actuator operably coupled to said second auxiliary wheel, said controller being configured to independently operate said actuators.

9. The patient transport apparatus of claim 1 , wherein said predetermined value associated with said desired load is determined based on calibration data developed during calibration of the patient transport apparatus without the patient.

10. The patient transport apparatus of claim 1 , wherein said sensing system comprises a sensor coupled to said controller to detect a motion condition of the patient transport apparatus, said controller being configured to deploy said auxiliary wheel based on said motion condition of the patient transport apparatus.

11. The patient transport apparatus of claim 10 , wherein said motion condition comprises one or more of: motion of the patient transport apparatus; direction of motion of the patient transport apparatus; duration of motion of the patient transport apparatus; and changes in velocity of the patient transport apparatus.

12. The patient transport apparatus of claim 1 , wherein said sensing system comprises a proximity sensor to detect obstacles.

13. The patient transport apparatus of claim 12 , wherein said controller is configured to operate said actuator to raise and lower said auxiliary wheel in response to the obstacles detected by said proximity sensor.

14. The patient transport apparatus of claim 1 , wherein said sensing system comprises a speed sensor to measure a rotational speed of said auxiliary wheel.

15. The patient transport apparatus of claim 14 , wherein said sensing system further comprises a second speed sensor to measure a rotational speed of one of said support wheels and said controller is configured to compare said rotational speed of said auxiliary wheel to said rotational speed of said one of said support wheels to determine if said auxiliary wheel is slipping on the surface.

16. The patient transport apparatus of claim 1 , wherein said controller is configured to generate said control signal such that all of said support wheels remains in contact with the surface.

17. The patient transport apparatus of claim 1 , wherein said controller is configured to apply said control signal to said actuator during transport to dynamically adjust said actuator during transport so that said force acting between said auxiliary wheel and the surface is maintained during transport.

18. The patient transport apparatus of claim 1 , wherein said controller is configured to change said predetermined value associated with said desired load during transport of the patient over the surface with the patient transport apparatus.

19. A patient transport apparatus for transporting a patient over a surface, said patient transport apparatus comprising:

a base;

support wheels coupled to said base and swivelable about swivel axes;

an auxiliary wheel assembly coupled to said base and comprising an auxiliary wheel configured to move between a stowed position spaced from the surface and deployed positions in contact with the surface, said auxiliary wheel assembly further comprising an actuator operably coupled to said auxiliary wheel to move said auxiliary wheel between said stowed position and said deployed positions;

a sensing system, said sensing system comprising a speed sensor to measure a rotational speed of said auxiliary wheel, and a second speed sensor to measure a rotational speed of one of said support wheels; and

a controller coupled to said sensing system to acquire a measurement associated with a current load applied to said auxiliary wheel, said controller configured to generate a control signal based on comparing said measurement to a predetermined value associated with a desired load, and to apply said control signal to said actuator thereby adjusting said current load relative to said desired load; and

wherein said controller is configured to compare said rotational speed of said auxiliary wheel to said rotational speed of said one of said support wheels to determine if said auxiliary wheel is slipping on the surface.