DC Motor Control Device Position Detection Accuracy
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Solution Overview
Problem
Conventional motor control devices using a DC motor and a one-phase rotary encoder suffer from reduced accuracy in position detection due to the inability to differentiate between intended and reverse rotations, leading to errors in position detection over time.
Innovation Solution
A motor control device that applies a predetermined voltage to the DC motor before it stops, allowing it to completely stop and then subtracts pulses generated after this point, ensuring accurate recognition of the rotation direction and preventing erroneous counting by the one-phase encoder.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a one-phase encoder is used to detect position, then device complexity is reduced, but measurement precision deteriorates due to inability to differentiate rotation direction
Solution Approach 1:
The controller applies a predetermined voltage to the DC motor before stopping to ensure complete cessation of rotation. This preliminary action prevents the motor from coasting backward due to inertia or magnetic attraction, which would cause the one-phase encoder to generate erroneous pulses that cannot be differentiated from valid rotation signals.
2Measurement precision
If voltage is applied until motor stops, then position accuracy is maintained, but energy consumption increases
Solution Approach 1:
The controller applies a predetermined voltage (which is lower than the voltage required to drive the load) to the DC motor after braking to ensure complete stop. This partial action provides just enough torque to overcome magnetic attraction and inertia without excessive energy consumption, achieving complete cessation of rotation while minimizing energy use.
Solution Approach 2:
The controller changes the voltage parameter applied to the motor based on the operational phase: full voltage during operation, reduced predetermined voltage during stopping to prevent reverse rotation. This parameter change optimizes both energy consumption and position accuracy by applying only the necessary voltage to achieve complete stop.
3Speed
If braking is applied to stop motor, then stopping time is reduced, but position accuracy deteriorates due to reverse rotation from magnetic attraction
Solution Approach 1:
The controller applies a predetermined voltage to the DC motor in opposition to the magnetic attraction force that causes reverse rotation during braking. This preliminary anti-action counteracts the attracting force between the magnet and coil, preventing the motor from rotating backward and ensuring the encoder accurately reflects the true stopping position.
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
This approach enhances the accuracy of position detection by distinguishing between forward and reverse rotations, thereby improving the overall precision of the motor control system.
Implementation Method 1
a lowest voltage necessary for rotating the DC motor against an attracting force between a magnet and a coil in the DC motor
Implementation Method 2
a one-phase encoder configured to generate a pulse according to rotation of the DC motor
Data Source
AI summary
A motor control device includes a counter that counts pulses output from a one-phase encoder according to rotation of a DC motor, and a controller that recognizes rotation number of the DC motor based on the number of pulses counted by the counter. After the DC motor is braked, the controller starts applying a predetermined voltage to the DC motor at first timing before the DC motor stops, and stops applying the predetermined voltage at second timing after the DC motor stops. The controller subtracts the number of pulses generated after the second timing from a value counted by the counter. The predetermined voltage is lower than a lowest voltage necessary for driving a driven object, and is higher than a lowest voltage necessary for rotating the DC motor against an attracting force between a magnet and a coil in the DC motor.