Motor Control Unit Commutation Time Extension for Stop Position Accuracy
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Solution Overview
Problem
Existing motor driving control methods face challenges in accurately controlling the rotational stop position of a motor, especially at high rotational speeds, due to inertia and load variations, leading to potential overrun and reduced positional accuracy.
Innovation Solution
A motor driving control device that includes a zero-cross detection unit for detecting back electromotive force and a control unit for performing 1-phase excitation-based commutation, extending the commutation time during deceleration steps until the motor reaches a predetermined speed, allowing precise control of the rotational stop position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the motor is stopped by turning off all switching elements to eliminate overrun, then the motor can stop without excessive current, but the back electromotive force periodically changes and the motor continues to rotate due to inertia, deteriorating positional accuracy
Solution Approach 1:
The control unit performs preliminary deceleration control before the motor stops, gradually reducing rotational speed to a predetermined value. This preliminary action allows the motor to enter a low-speed state where inertia effects are minimized, enabling accurate stop position control without the need for excessive current suppression measures.
Solution Approach 2:
The system dynamically switches between different control modes based on rotational speed. At high speeds, standard commutation control is applied; as speed decreases to the predetermined threshold, the control unit transitions to extended commutation time control. This dynamic adaptation optimizes performance across different operating conditions.
2Reliability
If hold current decay control is used to stop the motor with 2-phase excitation, then current can be gradually decreased to a stable point, but when rotational speed is high and inertia is large, the current periodically changes and the motor continues to rotate, failing to secure positional accuracy
Solution Approach 1:
The control unit changes the commutation time parameter based on rotational speed conditions. When the motor enters the deceleration phase and speed drops to the predetermined value, the commutation time is extended beyond the standard period. This parameter change ensures that current decay completes properly even during the transition to stop, preventing periodic current changes and securing positional accuracy.
3Reliability
If fast decay control is used to consume current in reverse direction to secure positional accuracy, then positional accuracy can be maintained when current is excessive, but it becomes impossible to secure positional accuracy when motor inertia exceeds one quadrant of electrical angle
Solution Approach 1:
The control unit performs preliminary deceleration to reduce rotational speed to a predetermined value before the motor stops. This preliminary action reduces the inertia effect to within manageable limits (one quadrant or less), making the motor responsive to commutation control and enabling accurate stop position control without requiring fast decay control's aggressive current suppression.
Solution Approach 2:
The control method skips the need for aggressive fast decay control by rushing through the deceleration phase with extended commutation timing. This allows the system to pass through the high-inertia phase quickly and enter the low-speed phase where standard commutation control is sufficient for accurate stopping.
4Ease of operation
If open control of 1-phase excitation is used with fixed rotational speed before stop, then commutation can be performed, but the rotational speed is not optimum for the load and the time for vibration to subside varies, making it difficult to accurately control the stop position
Solution Approach 1:
The control unit uses feedback from rotational speed detection to determine when to extend commutation time. By monitoring the actual rotational speed and comparing it to the predetermined threshold, the system automatically adjusts commutation timing to ensure accurate stopping, eliminating the need for manual optimization of speed and timing parameters.
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 accurate and rapid control of the motor's rotational stop position, reducing the risk of overrun and maintaining positional accuracy across varying loads and speeds, while suppressing current ripple and electromagnetic noise.
Implementation Method 1
a zero-cross detection unit configured to detect zero-cross of back electromotive force of a motor coil provided in a motor
Data Source
AI summary
A rotational stop position of a motor is accurately controlled. A motor driving control device (100) includes a BEMF detection unit (118) for detecting zero-cross of back electromotive force of a motor coil provided in a motor, and a CPU (101) for controlling driving of the motor by a 1-phase energization method and, without a position sensor, performing commutation based on the zero-cross of the back electromotive force detected by the BEMF detection unit (118), controlling driving of the motor based on a rotational speed corresponding to a drive voltage and a load, and performing extension control of a commutation time for each step from a calculated deceleration start step until the rotational speed of the motor decreases to a predetermined rotational speed or less for enabling the motor to stop at a desired stop position when the driving of the motor is stopped.