Digital Motor Control via PWM Null Point Stability
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Solution Overview
Problem
Existing motor control systems face inefficiencies, particularly at the null point between forward and reverse directions, leading to high power dissipation and instability, especially in closed-loop servo systems, limiting their application in power-constrained environments.
Innovation Solution
A digital motor control system using pulse width modulation (PWM) with a clock pulse generator, variable duration pulse generator, and logic control to synchronize and vary output pulses, allowing for efficient control of motor direction and speed through a spring-loaded joystick or similar variable control element, reducing power loss and enhancing stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a linear or analog servo loop is used to control motor speed and direction by controlling the amplitude and polarity of a signal applied to a power transistor, then motor speed and direction can be controlled, but the power transistor dissipates a lot of power especially around the null error signal level
Solution Approach 1:
The patent applies periodic pulse width modulation (PWM) to control the motor. Instead of using continuous analog signals that cause continuous power dissipation, the system uses periodic pulses where the duty cycle varies the average power delivered to the motor. The power transistor switches on and off periodically, minimizing the time it spends in the high-dissipation linear region and thereby reducing power loss especially around the null position.
Solution Approach 2:
The patent replaces the analog continuous control mechanism with a digital pulse-based control system. By substituting the analog amplitude and polarity control with digital pulse width and frequency modulation, the system achieves more efficient power switching and reduced dissipation in the power transistor, particularly at the null error signal level.
2Ease of operation
If a non-linear servo loop is used to utilize an error signal to induce full forward or reverse motor rotation, then motor rotation can be controlled, but stabilization is difficult because there is no continuous error signal provided at the null position creating a dead space
Solution Approach 1:
The patent uses periodic PWM pulses to provide continuous control information even at the null position. The periodic nature of the pulses ensures that the motor receives continuous directional guidance, eliminating the dead space problem in non-linear servo loops where the null position creates stabilization difficulties.
Solution Approach 2:
The patent implements a feedback mechanism where the pulse width or frequency is continuously adjusted based on the error signal. This feedback ensures that even at the null position, the motor receives appropriate control signals to maintain stability, preventing the dead space issue that occurs in non-linear systems where no continuous error signal is provided.
3Loss of energy
If pulse width variation type of control is used in open loop systems to efficiently use power, then power efficiency is improved, but the motor cannot reverse automatically in closed loop servo systems especially around null
Solution Approach 1:
The patent employs periodic PWM control that can automatically adjust the pulse pattern to achieve motor reversal. By varying the pulse width and frequency periodically based on the error signal, the system maintains power efficiency while enabling automatic reversal capability in closed-loop servo applications, overcoming the limitation of open-loop pulse width variation systems.
Solution Approach 2:
The patent makes the pulse width and frequency dynamic rather than fixed. The control system continuously adjusts the PWM parameters based on the motor's actual position and speed feedback, enabling the motor to reverse automatically when needed while maintaining efficient power usage. This dynamic adaptation allows the system to work effectively in closed-loop servo applications.
Data Source
AI summary
A digital motor control system utilizes time duration electric pulses generated by digital logic to control the motor speed and direction of rotation of a D.C. or A.C. motor. The digital logic produces width modulated pulses that can be connected to large or small electric motors by mechanical or electrical relays or switches to provide efficient motor control with little control circuit power loss. The mechanical or electrical switches are responsive to the digital logic to change motor direction or remove power from the motor windings. A variable control element such as a computer joystick can be utilized to control both direction and speed of the motor. The system can be configured as an open loop system or as a closed loop servo with a feed back element to control the rotational position of the motor.