Stepper Motor Current Shaping for Accurate Rest Position Control
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Solution Overview
Problem
Stepping motors vibrate at every driving step, making it difficult to achieve accurate stop position control, especially in applications like chip mounters where the next driving sequence is initiated before vibration damping is complete, leading to significant gaps between the intended and actual stop positions.
Innovation Solution
A motor control device that adjusts the drive current to a stepping motor by gradually changing from an initial value to a target current over a longer period, then overshooting and returning to the target current, using a digital to analog converter, comparator, and control signal generation units to manage the drive current effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the drive current is instantly switched from initial value to target drive current value, then the motor reaches the target drive position quickly (short motor drive reference period), but the motor vibrates significantly at each driving step, making accurate stop position control impossible
Solution Approach 1:
The system performs preliminary action by gradually changing the drive current from initial value to target drive current value over a longer time period before the motor completes its movement. This preliminary current adjustment suppresses vibrations that would otherwise occur with instant current switching, enabling accurate stop position control while maintaining efficient motor operation.
2Manufacturing precision
If micro-step drive is used to gradually switch excitation state, then motor vibration is suppressed, but the rotor stops before reaching the original resting position due to decreased moment of inertia
Solution Approach 1:
The system changes the drive current parameter dynamically during motor operation. It gradually increases current from initial to target value during acceleration to suppress vibrations, then applies overshoot control where current exceeds target value temporarily to compensate for reduced moment of inertia effects, ensuring the rotor reaches and stops at the correct position.
Solution Approach 2:
The system applies excessive action through current overshoot control, where the drive current temporarily exceeds the target drive current value after the motor reaches the target position. This excessive current application compensates for the reduced moment of inertia effect caused by gradual current switching, ensuring the rotor reaches the intended resting position rather than stopping short.
3Productivity
If the next driving sequence is started before vibration damping is complete, then productivity is maintained, but a large gap appears between original stop position and actual position when position information is read
Solution Approach 1:
The system performs preliminary vibration suppression action by gradually adjusting drive current before the motor completes its movement and before the next driving sequence begins. This allows continuous high-speed operation while ensuring vibrations are suppressed and position accuracy is maintained, eliminating the need to wait for vibration damping.
Solution Approach 2:
The system applies excessive current temporarily during and after the driving sequence to counteract vibrations that occur during rapid operation. This allows the next driving sequence to start immediately (maintaining productivity) while the overshoot control ensures the motor reaches and holds the correct position despite ongoing vibrations.
Data Source
AI summary
To provide a motor control device, a motor control method and a non-transitory storage medium storing a motor control program for a motor control device, capable of controlling the resting position of a motor with higher accuracy. A motor control device includes:a circuit; anda digital to analog converter configured to generate a target voltage value, wherein;the circuit includes:a first adjustment unit configured to adjust a drive signal in a manner that a drive current changes to a target drive current value over a longer time than a period until a motor reaches a target drive position when the drive current is switched to a target drive current value; anda second adjustment unit configured to adjust the drive signal in a manner that a overshoots a current value greater than the target drive current value and then returns to the target drive current value.