Algorithm for power drive speed control

• US 7,953,537 B2
• Filed: 02/29/2008
• Issued: 05/31/2011
• Est. Priority Date: 02/29/2008
• Status: Expired due to Fees

• Current Assignee: Hill-Rom Services Incorporated (Baxter International Inc.)
• Original Assignee: Hill-Rom Services Incorporated (Baxter International Inc.)
• Inventors: Bhai, Aziz A.
• Primary Examiner(s): ARTHUR JEANGLAUD, GERTRUDE
• Application Number:
  US12/040,446
• Publication Number:
  US 20090222184A1
• Time in Patent Office: 1,187 Days
• Field of Search: 701/33, 701/36, 701/70, 701/79, 180/293, 180/276, 561/7, 561/8, 5 8/11.R
• US Class Current: 701/70
• CPC Class Codes: A61G 2203/36 for motion
• CPC Class Codes: A61G 7/018 Control or drive mechanisms
• CPC Class Codes: A61G 7/08 Apparatus for transporting beds
• CPC Class Codes: H02P 23/0077 Characterised by the use of a particular software algorithm
• CPC Class Codes: H02P 25/00 Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details

Abstract

A control system for a self-propelled patient-support apparatus includes a controller that utilizes a power drive speed control algorithm to control the power output to a motor of a drive mechanism for driving the patient-support apparatus across a floor. The control algorithm normalizes a force input by a user on a user input device, the force indicative of a desired drive speed. The algorithm varies the responsiveness of the output to the drive mechanism based on the current operating conditions of the drive mechanism.

Claims

1. A control system for a self-propelled patient-support apparatus comprising

a user input device,

a motor for driving a wheel over a floor, and

a controller including a processor and a memory device including instructions that, when executed by the processor, (i) monitor the user input device to determine a speed input request from a user, (ii) determine a desired direction of movement of the patient-support apparatus across the floor, (iii) normalize the speed input request, (iv) compare the normalized speed input request to a threshold value, (v) calculate an effective speed input value by evaluating a current speed input request and a previous speed output value, (vi) apply a speed transfer function to the effective speed input value to determine a current raw speed output value, (vii) scale the current raw speed output value based on the desired direction of movement to determine a current scaled speed output, (viii) weight the current scaled speed output with the previous speed output value to determine a current speed output value to transmit to the motor.

2. The control system of claim 1, wherein the memory device further includes instructions that normalize the speed input request based on a desired direction of travel of the patient-support apparatus.

3. The control system of claim 1, wherein the memory device further includes instructions that normalize the speed input based on the value of the speed input request compared to a value of a previous speed input request.

4. The control system of claim 1, wherein the memory device further includes instructions that normalize the speed input based on the value of the speed input request as compared to a condition in which there is no speed input request.

5. The control system of claim 1, wherein the memory device further includes instructions that apply a strain gage constant to normalize the speed value request.

6. The control system of claim 1, wherein the speed transfer function may vary over time.

7. The control system of claim 1, wherein the speed transfer function is calculated based on the normalized speed input request and a previous speed output value.

8. The control system of claim 1, wherein the memory device further includes instructions that (ix) vary the speed transfer function if the normalized input exceeds a transfer function change threshold.

9. The control system of claim 1, wherein the scaling of the speed is based on an intended use environment of the particular patient-support apparatus.

10. The control system of claim 1, wherein the weighting of the current scaled output speed value decreases as the value of the previous speed output value increases.

11. The control system of claim 1, wherein the user input device comprises a load cell.

12. The control system of claim 1, wherein the user input device comprises an enable switch.

13. A patient-support apparatus comprising

a frame,

a drive mechanism coupled to the frame and configured to move the patient-support apparatus across a floor, the drive mechanism including a drive wheel and a motor to drive the wheel,

a controller coupled to the motor, and

a user input coupled to the controller and configured to provide an input indicative of the speed and direction a user wishes to move the patient-support apparatus,

wherein the controller includes a processor and a memory device including instructions that, when executed by the processor, (i) monitor the user input device to determine a speed input request from a user, (ii) determine a desired direction of movement of the patient-support apparatus across the floor, (iii) normalize the speed input request, (iv) compare the normalized speed input request to a threshold value, (v) calculate an effective speed input value by evaluating a current speed input request and a previous speed output value, (vi) apply a speed transfer function to the effective speed input value to determine a current raw speed output value, (vii) scale the current raw speed output value based on the desired direction of movement to determine a current scaled speed output, (viii) weight the current scaled speed output with the previous speed output value to determine a current speed output value to transmit to the motor.

14. The patient-support apparatus of claim 13, wherein the drive mechanism further includes a motor controller configured to receive the current speed output value and to power the motor based on the current speed output value.

15. A method of controlling the speed and direction of travel of a self-propelled patient-support apparatus including a variable user input device configured to receive a user input indicative of the direction and speed of travel, the method comprising the steps of

monitoring the variable user input device to determine a speed input request from a user,

determining a desired direction of movement of the patient-support apparatus,

normalizing the speed input request,

comparing the normalized speed input request to a threshold value,

calculating an effective speed input value by evaluating a current speed input request and a previous speed output value,

applying a speed transfer function to the effective input to determine a current raw speed output value,

scaling the current raw speed output value based on the desired direction of movement to determine a current scaled speed output, and

weighting the current scaled speed output with the previous speed output value to determine a current speed output value to transmit to a motor.

16. The method of claim 15, wherein the weighting of the current scaled output speed value decreases as the value of the previous speed output value increases.

17. The method of claim 15, wherein the step of applying a speed transfer function applies a speed transfer function that varies based on the normalized speed input request and the value of a previous speed output value.

18. The method of claim 15, wherein the step of normalizing the speed input normalizes the speed input based on the value of the speed input request and the value of a previous speed input request.

19. The method of claim 15, wherein the step of normalizing the speed input normalizes the speed input based on the value of the speed input request compared to a condition in which there is no speed input request.

20. The method of claim 15, wherein the step of normalizing the speed input normalizes the speed input based on a strain gage constant.

21. The method of claim 20, wherein the strain gage constant varies depending on the determined desired direction of movement of the patient-support apparatus.