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

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.

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.