Torque Motor Drive Circuit for Wire EDM Using PWM Bridge Control
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Solution Overview
Problem
Existing torque motor driving circuits for wire cut electrical discharge machines face issues with large torque fluctuations, high production costs, and reliability concerns due to the use of resistor voltage divider and triac methods, while inverter methods require complex circuits and high-capacitance electrolytic capacitors that can lead to heat generation and leakage.
Innovation Solution
A torque motor driving device using a full-wave rectifying circuit, a bridge circuit with semiconductor switches, a polarity determination signal generating circuit, and a PWM signal generating circuit to adjust the duty of the PWM signal based on torque requirements, eliminating the need for high-capacitance capacitors and complex duty adjustment circuits, and ensuring stable low-torque output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the triac method is used to control torque motor voltage, then power loss is reduced and current control accuracy is improved, but torque fluctuations increase significantly when low torque is required
Solution Approach 1:
The patent applies periodic PWM (Pulse Width Modulation) action to control the torque motor. By switching the voltage on and off at high frequency with controlled duty cycle, the system achieves smooth average torque control without the large fluctuations inherent in triac phase control. This periodic switching action allows precise torque regulation while maintaining stable motor operation.
Solution Approach 2:
The patent dynamically adjusts the duty cycle of PWM signals based on the required torque level. By varying the ON time proportion of the switching signals in real-time, the system can smoothly control torque from high to low levels without the firing angle limitations of triac control, thereby maintaining torque stability even at low torque requirements.
2Stability of the object's composition
If the inverter method with PWM control is used, then torque fluctuations are reduced, but the device complexity and production cost increase due to required duty adjustment circuits
Solution Approach 1:
The patent makes the bridge circuit serve multiple functions: it performs both voltage rectification and PWM-based torque control without requiring separate duty adjustment circuits. The same semiconductor switches in the bridge circuit handle both the rectification of AC input and the PWM modulation for torque control, eliminating additional complexity while maintaining torque stability.
Solution Approach 2:
The patent merges the rectification function and the PWM control function into a single bridge circuit. By combining these functions, the system achieves smooth torque control with reduced fluctuations while avoiding the need for separate duty adjustment circuits that would increase device complexity and production cost.
3Stability of the object's composition
If high-capacitance electrolytic capacitors are used in inverter circuits, then stable DC voltage is achieved, but heat generation and leakage risks increase
Solution Approach 1:
The patent extracts and eliminates the high-capacitance electrolytic capacitor from the circuit. By using PWM control directly on the bridge circuit output, the system achieves stable voltage control without requiring large capacitors for smoothing, thereby removing the source of heat generation and leakage risks associated with high-capacitance electrolytic capacitors.
Solution Approach 2:
The patent replaces the expensive and unreliable high-capacitance electrolytic capacitor with a capacitor-free PWM control scheme. This substitution uses simpler, more reliable components that do not suffer from heat generation and leakage issues, improving long-term reliability while reducing production costs.
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 provides a stable low-torque output with long-term reliability and reduced production costs by applying a sinusoidal voltage waveform directly to the torque motor using a bridge circuit with semiconductor switches, minimizing torque fluctuations and power losses.
Implementation Method 1
a full-wave rectifying circuit (30) that performs full-wave rectification on the power voltage V1
Implementation Method 2
a bridge circuit (48) that applies the rectified voltage to the single-phase torque motor (20)
Data Source
Figure 1
Figure 2~3(b)
Figure 4(a)~4
AI summary
In a torque motor driving device for wire cut electrical discharge machines, a voltage waveform rectified by a full-wave rectifying circuit, not using a high-capacitance electrolytic capacitor, is applied as an AC voltage to a single-phase torque motor by a bridge circuit including semiconductor switches. A PWM signal whose duty is adjusted so that the current flowing through the torque motor matches an instructed value is generated and the generated PWM signal is used for the operation of the bridge circuit.