Chapter 3
Theory of Operation
P/N 57150002, Revision 5.0 3 - 35 Trimble S, VX, SPS & RTS Service Manual
F
Trimble servo system
To drive the motor a current is sent through the motor winding and generates a force to move the
motor (magnet holder or motor winding) forward.
The winding is divided in three phases to make it possible to control the movement of the motor. A
specific servo calibration procedure is made to detect the different magnetic fields for the motor
movement.
The motor has three different working modes:
• Driving mode. Where movement is controlled by servo knobs or system process.
• Friction mode. Where the motor allows the instrument to be turned manually. The magnetic
friction will generate a resistance against movement of the motor.
• Holding mode. Where the motor works as a clutch to lock the instrument position and prevent
movements, e.g when pressing a push-button as long as no positioning commands is given.
Positioning and control of the servo system is made by the processor board. The processor board also
contains firmware for the servo system.
Accelerometer
The horizontal servo system also contains two accelerometers, these accelerometers senses the
movement (vibration) of the instrument and send this information back to the servo system to increase
stability. The accelerometer removes certain frequencies and thereby eliminates undesired vibrations.
The two accelerometers compensates for e.g. mechanical weaknesses in the tripod.
Accelerometer no1 (front accelerometer) is positioned inside the TCU attachment and accelerometer
no2 (side accelerometer) is positioned inside the battery side cover.
Calibration
After replacement / removal & assembling of MSB board with motor winding / SRC board with
magnets / Accelerometers a calibration procedure must be made, this is done in PASS
The calibration detects the position of the magnetic field with respect to the electrical field in order
to be able to commutate the current correctly. The data is stored together with the instrument angles
corresponding to the working field.
Service
Maintenance
• Servo and angle system calibration (PASS)
Replacement of spare parts
• SRC board incl. magnets
• MSB board incl. motor winding
• Accelerometers
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