Stepper Motor Drive with Slipping Clutch for Geodetic Instruments
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Solution Overview
Problem
Geodetic surveying instruments face challenges in achieving precise and accurate motorized movement while minimizing size and effort, avoiding jerks and resonances, and protecting against external forces and overload, which can damage the mechanical system.
Innovation Solution
A geodetic surveying instrument with a motorized movement axis featuring a stepper motor driven by a field-oriented control system, coupled with a gear reduction and slipping clutch arrangement, which provides a self-locking transmission and prevents damage from excessive torque, ensuring smooth and accurate movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a motorized drive unit is used to achieve precise and accurate movement, then measurement precision is improved, but the risk of mechanical damage from external forces and overload increases
Solution Approach 1:
A slipping clutch is integrated into the drive train between the motor and the measurement axis to provide overload protection. The clutch is designed to slip when excessive torque is applied, preventing damage to the motor and mechanical components while allowing the system to continue operating. This beforehand cushioning mechanism protects the precision measurement system from external forces and overload conditions.
2Measurement precision
If a stepper motor with gear reduction is used to achieve precise positioning, then positional accuracy is improved, but device complexity increases
Solution Approach 1:
The drive system combines a stepper motor, gear reduction mechanism, and slipping clutch into a single integrated drive unit. This merging of components achieves precise positioning through gear reduction while the slipping clutch simultaneously provides overload protection. The field-oriented control system integrates motor control with position feedback from an encoder, creating a unified control architecture that manages the entire drive system with a single controller, thereby reducing overall system complexity.
Solution Approach 2:
An encoder is mounted on the motor shaft to provide feedback on motor position and speed to the field-oriented control system. This feedback enables precise control of the stepper motor's position and velocity, allowing the system to achieve high positional accuracy while the controller can also detect and respond to overload conditions by controlling the motor current, thereby protecting the mechanical components.
3Measurement precision
If field-oriented control is used to achieve smooth movement and reduce resonances, then measurement precision is improved, but use of energy increases
Solution Approach 1:
The field-oriented control system uses periodic PWM (pulse-width modulation) switching to control the motor phases, enabling smooth and accurate motor control with reduced resonances. The controller periodically switches the motor current in a controlled manner to achieve the desired torque and position, reducing mechanical vibrations that could affect measurement accuracy. The slipping clutch periodically engages and disengages under varying load conditions, providing mechanical damping that further reduces resonances.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables precise positioning and fast rotation with improved dynamic behavior, reduced noise, and energy efficiency, maintaining high positional accuracy and stiffness while preventing mechanical damage, thus enhancing the instrument's measurement accuracy and reliability.
Implementation Method 1
a motorized movement axis with a stepper motor
Implementation Method 2
coupled with a gear reduction and slipping clutch arrangement, which provides a self-locking transmission
Implementation Method 3
slipping clutch arrangement, which provides a self-locking transmission and prevents damage from excessive torque
Data Source
AI summary
A geodetic surveying instrument to move a measurement light beam into a desired measurement direction in space, comprising at least one movement axis which is motorized, providing a positioning of the measurement direction of the geodetic surveying instrument, and an instrument-encoder at the movement axis configured for deriving the measurement direction as a measurement value of the geodetic surveying instrument. The geodetic surveying instrument comprises a transmission link of the movement axis of the geodetic surveying instrument to a motor axis of a stepper motor, which transmission link is configured with a gear reduction and a slipping clutch arrangement, and wherein the stepper motor comprises a rotational motor-encoder on its motor-axis and is driven by a motor controller that provides a field oriented control of phase currents of the stepper motor, which field orientation is derived based on the rotational motor-encoder.