Position control arrangement, especially for a surveying instrument, and a surveying instrument

• US 20090133273A1
• Filed: 11/10/2008
• Published: 05/28/2009
• Est. Priority Date: 09/20/2002
• Status: Active Grant

• Current Assignee: Trimble AB (Trimble Inc.)
• Original Assignee: Trimble AB (Trimble Inc.)
• Inventors: Berg, Ulf, Hertzman, Mikael, Westermark, Magnus, Klang, Thomas
• Granted Patent: US 7,765,084 B2
• Time in Patent Office: Days
• US Class Current: 33/281
• CPC Class Codes: G01C 1/00 Measuring angles
• CPC Class Codes: G01C 15/00 Surveying instruments or accessories not provided for in groups G01C1/00 - G01C13/00
• CPC Class Codes: G01C 15/002 Active optical surveying means optical plumbing G01C15/105
• CPC Class Codes: G05B 19/19 characterised by positioning or contouring control systems, e.g. to control position from one programmed point to another or to control movement along a programmed continuous path
• CPC Class Codes: G05B 2219/42091 Loop combinations, add a second loop, cascade control
• CPC Class Codes: G05B 2219/42104 Loop switch, speed loop then position loop, mode switch
• CPC Class Codes: G05B 7/02 electric
• CPC Class Codes: G06F 15/00 Digital computers in general details G06F1/00 – G06F13/00; Data processing equipment in general

Abstract

In a position control arrangement for controlling the rotational position of a movable unit, especially for a surveying instrument, an electric motor is arranged to rotate the movable unit around an axis of rotation, and there are controllers for enabling the motor to stop the movable unit in a desired rotational position. The motor is a direct drive motor, the shaft of which forms the axis of rotation for the movable unit, and the motor is arranged to selectively operate in either a first, normal mode for rotating the movable unit to a desired position, or in a second, friction mode for providing resistance to a forced rotation of the movable unit from a predetermined position to a new position. A control unit detects the presence of a forced rotation and automatically changes the mode of operation in response thereto.

Claims

1. An apparatus for controlling angular movement of a movable unit between an existing angular position and a desired angular position, comprising

an electric direct drive motor adapted to rotate said movable unit, said motor having a shaft defining an axis of rotation of the movable unit and being selectively operable in one of a normal mode for rotating said movable unit to a desired position and a friction mode permitting incident force to rotate said movable unit from said desired position to a new position;

a mode control unit to enable said friction mode of said motor upon the application of said incident force; and

a friction control unit connected to said motor in said friction mode, and disconnected from said motor in said normal mode.

2. The apparatus of claim 1 in which said friction control unit is operative upon application of said incident force to cause said motor to resist rotation of said movable unit at a predetermined magnitude of resistance.

3. The apparatus of claim 1 comprising, in addition, a position detector to detect the angular position of the movable unit.

4. A controller for controlling a direct drive motor having a rotating shaft, the controller comprising:

input means for receiving an intended rotational position of said rotating shaft of said motor;

position detecting means for detecting an actual rotational position of said rotating shaft;

control means for controlling said rotating shaft to rotate from said actual rotational position of said rotating shaft to said intended rotational position of said rotating shaft; and

friction control means for causing said motor to produce a torque resisting a manually forced rotation of said rotating shaft while said rotating shaft is manually rotated to a new rotational position, wherein

said control means automatically connects said motor to said friction control means in response to a detection of said manually forced rotation of said rotating shaft to said new position, and automatically disconnects said motor from said friction control means when said new rotational position is reached.

5. An apparatus for controlling rotational position of a movable unit about an axis of rotation, comprising:

a motor for controllably applying torque to move the movable unit about the axis;

a position detector to detect actual rotational position of the movable unit;

a control circuit for selectively operating the motor in one of a normal mode and a friction mode, wherein (1) in the normal mode the control circuit is responsive to a difference between actual rotation position and an intended rotational position of the movable unit for controlling the motor to rotate the movable unit to the intended rotational position, and (2) in the friction mode the control circuit controls the motor to apply a torque resisting change of rotational position of the movable unit while permitting incident force to rotate the movable unit.

6. The apparatus of claim 5, wherein the control circuit is operative to selectively change operation of the motor from the normal mode to the friction mode when incident force causes rotation of the movable unit.

7. The apparatus of claim 5, wherein the control circuit comprises a mode control unit responsive to rate of change of actual rotational position caused by incident force for selectively changing operation of the motor from the normal mode to the friction mode.

8. The apparatus of claim 7, wherein the control circuit comprises a friction control unit responsive to the position detector for determining a magnitude of the torque applied in the friction mode.

9. The apparatus of claim 8, wherein the friction control unit determines the magnitude of the torque applied in said friction mode as a function of acceleration of incident forced rotation of the movable unit.

10. The apparatus of claim 9, wherein the friction control unit determines the magnitude of the torque applied in the friction mode as a function of velocity of incident forced rotation of the movable unit.

11. The apparatus of claim 8, wherein the friction control unit comprises a derivating module responsive to the position detector for determining a rate of change of angular position of the movable unit in the friction mode.

12. The apparatus of claim 11, wherein the friction control unit comprises a proportioning module for determining torque required in the friction mode to resist change of rotational position of the movable unit while permitting incident force to rotate the movable unit.

13. The apparatus of claim 12, wherein the friction control unit comprises a limiting module for limiting the torque applied by the motor to the movable unit in the friction mode.

14. The apparatus of claim 8 further comprising a switch, the mode control unit controlling the switch to connect the motor to the friction control unit in the friction mode and to disconnect the motor from the friction control unit to enable the normal mode.

15. A survey instrument comprising:

a housing;

a movable unit rotatable back and forth around a first axis relative to said housing, and including survey optical equipment; and

a first position control system for controlling the angular position of said movable unit, said first position control system comprising a first motor to rotate said movable unit about said one axis and a control circuit selectively to operate said first motor in one of a normal mode, in which said first motor rotates said movable unit to a desired position, and a friction mode in which said first motor applies a torque to said movable unit resisting change of angular position of said movable unit caused by incident force while permitting incident force to rotate said movable unit.

16. The survey instrument of claim 15 in which said first motor is a direct-drive electric motor having a shaft coincident with said one axis.

17. The survey instrument of claim 15 comprising, in addition, a second direct-drive electric motor having a shaft coincident with a second axis relative to said housing and in which said movable unit is selectively rotatable back and forth around said second axis.

18. The survey instrument of claim 17 in which said one axis is a horizontal axis and said second axis is a vertical axis.

19. The survey instrument of claim 18 in which said first position control system controls the angular position of said movable unit about each of said horizontal and vertical axes.

20. The survey instrument of claim 19 in which said first motor rotates said movable unit about said horizontal axis and said second motor rotates said movable unit about said vertical axis.

21. The survey instrument of claim 20 comprising, in addition, position detectors associated with each of said horizontal and vertical axes to detect actual angular position of said movable unit relative to each of said axes.

22. The survey instrument of claim 21 further comprising a second position control system, said second position control system comprising said second motor and a control circuit selectively to operate said second motor in one of said normal and said friction modes.