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

• US 7,634,381 B2
• Filed: 03/18/2005
• Issued: 12/15/2009
• 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
• Primary Examiner(s): Nghiem; Michael P
• Application Number:
  US11/084,797
• Publication Number:
  US 20050187734A1
• Time in Patent Office: 1,733 Days
• Field of Search: 702/94, 702/95, 702150-153, 700/192, 700/193
• US Class Current: 702/151
• 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

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. A method for controlling angular movement of a movable unit between an existing angular position and a desired angular position, the method comprising:

deriving an error signal representing an angular difference between the existing position and the desired position of the movable unit;

generating a first voltage from the angular movement of the movable unit caused by incident force;

comparing said error signal and said first voltage to a respective predetermined threshold amount;

generating a second voltage when either said error signal or said first voltage exceeds the respective predetermined threshold amount; and

causing said second voltage to induce an angular force on the movable unit counter to said angular movement caused by said incident force.

2. The method of claim 1 wherein said error signal is obtained by

monitoring the existing angular position of the movable unit;

introducing the desired angular position for the movable unit; and

comparing said existing angular position and said desired angular position to derive a difference representing said error signal.

3. The method of claim 2, comprising changing the angular position of the movable unit until said error signal is substantially zero.

4. The method of claim 1 in which said induced angular force is sufficient to retard the angular movement of the movable unit caused by said incident force.

5. The method of claim 4 in which said second voltage is generated by

determining rates of change of angular movement of the movable unit caused by said incident force;

calculating from said rates of change of angular movement caused by said incident force corresponding values representing said induced angular force;

filtering said corresponding values to pass values less than a predetermined threshold value; and

generating said second voltage based upon said passed values.

6. The method of claim 5 comprising monitoring said rates of change of angular movement of the movable unit caused by said incident force and determining therefrom a velocity of angular movement of the movable unit caused by said incident force.

7. The method of claim 6 in which said induced angular force is applied to the movable unit in opposition to the angular movement of the movable unit caused by said incident force if said induced angular force is less than a predetermined value.

8. The method of claim 7 in which said second voltage is not generated when said velocity of angular movement of the movable unit caused by said incident force is less than a predetermined threshold amount, the desired angular position being reset as the existing angular position of the movable unit when said velocity of angular movement of the movable unit caused by said incident force is substantially zero.

9. The method of claim 8 in which said second voltage drives an electric motor adapted to apply said induced angular force to the movable unit.

10. The method of claim 9 in which said electric motor is a direct-drive motor.

11. A computer system for controlling angular movement of a movable unit between an existing angular position and a desired angular position, the computer system including a processor and a computer recording medium including computer executable code executable by said processor, the computer executable code comprising:

code for deriving error data representing an angular difference between the existing position and the desired position of the movable unit;

code for monitoring data representing a voltage value derived from the angular movement of the movable unit caused by incident force;

code for comparing said error data and said voltage value with a respective predetermined threshold amount; and

code for generating a control signal when either said angular difference error or said voltage value exceeds the respective predetermined threshold amount.

12. The computer system of claim 11 comprising, in addition, means for generating a control voltage when said control signal is present, said control voltage causing an angular force induced on the movable unit sufficient to retard said angular movement of the movable unit caused by said incident force.

13. The computer system of claim 12 further comprising code for determining the rate of change of angular movement of the movable unit caused by said incident force, and calculating therefrom a velocity of angular movement of the movable unit caused by said incident force.

14. The computer system of claim 13 further comprising code for calculating from said rate of change of angular movement caused by said incident force a value representing said induced angular force, and means for inducing said angular force on the movable unit in opposition to said angular movement of the movable unit caused by said incident force.

15. The computer system of claim 14 comprising, in addition, code for comparing said induced angular force to a predetermined value and generating a control signal to discontinue said induced angular force when it is greater than a predetermined value.

16. The computer system of claim 15 further comprising code for monitoring said velocity of angular movement of the movable unit caused by said incident force, and code for setting said control voltage to substantially zero when said velocity of angular movement of the movable unit caused by said incident force is substantially zero.

17. Apparatus for controlling angular movement of a movable unit between an existing angular position and a desired angular position, comprising:

a first comparator receiving signals representing the existing and desired angular positions, said first comparator producing an error signal representing an angular difference between the existing position and the desired position of the movable unit;

a first voltage control circuit responsive to the angular movement of the movable unit caused by incident force to produce a first voltage;

a second comparator receiving said error signal and said first voltage, said second comparator producing a control signal when either said error signal or said first voltage exceeds a respective predetermined threshold amount; and

a second voltage control circuit receiving said control signal and producing a second voltage representative of an angular force sufficient to retard angular movement of the movable unit caused by said incident force.

18. The apparatus of claim 17 comprising, in addition, a motor driven by said first voltage when said first voltage is less than said predetermined threshold amount to cause angular movement of the movable unit in one direction toward the desired angular position.

19. The apparatus of claim 18 in which said second voltage is connected to drive said motor to apply said angular force to retard said angular movement of the movable unit caused by said incident force.