Motor Control Device for Machine Tool Power Failure Protection
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Solution Overview
Problem
Machine tools face challenges in securely stopping feed shaft motors during power failures on the AC power supply side, leading to potential collisions and increased heat generation in main shaft motors due to uncontrolled DC voltage fluctuations.
Innovation Solution
A control device with a determination unit and excitation command unit that outputs an excitation current command to the main shaft motor when specific conditions are met, allowing for early deceleration of the feed shaft motor and stabilization of DC voltage during power failures, thereby preventing collisions and reducing heat generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the feed shaft motor is stopped immediately upon detecting power failure on the AC power supply side, then collision of the feed shaft is prevented, but the DC voltage on the DC link fluctuates uncontrollably causing heat generation in the main shaft motor
Solution Approach 1:
The control device determines in advance whether the main shaft motor is in a rapid traverse mode before power failure occurs. When rapid traverse is detected, the control device prepares to output excitation current to the main shaft motor upon power failure, enabling the motor to generate braking force and control DC voltage. This preliminary determination allows the system to switch control strategies based on the operational state, preventing both feed shaft collision and main shaft motor overheating.
2Temperature
If excitation current is output to the main shaft motor during power failure, then DC voltage is stabilized and heat generation is reduced, but the control device complexity increases
Solution Approach 1:
The control device changes the excitation current parameter of the main shaft motor based on the operational mode detected before power failure. When rapid traverse mode is detected, the control device outputs excitation current during power failure to enable braking and stabilize DC voltage. When not in rapid traverse mode, excitation current is not output. This parameter change approach allows the system to maintain simplicity by only activating additional control functions when necessary.
3Measurement precision
If the control device monitors feed shaft motor operation status continuously, then accurate determination for excitation current output is achieved, but the loss of time for power failure response increases
Solution Approach 1:
The control device performs preliminary determination of the feed shaft motor's operational status (whether in rapid traverse mode) before power failure occurs. This advance determination allows the control device to immediately respond to power failure by outputting excitation current to the main shaft motor without requiring complex real-time analysis during the power failure event, thus achieving both accurate determination and rapid response.
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 control device enables secure early stopping of feed shaft motors and reduces heat generation in main shaft motors during power failures, ensuring safe operation and preventing collisions by managing DC voltage fluctuations effectively.
Implementation Method 1
a converter converting (rectifying) AC power supplied from the three-phase AC power supply side for outputting DC power
Implementation Method 2
inverters connected to a DC link (a direct-current link) as the DC side of the converter, and mutually converting power between DC power of the DC link, and AC power
Implementation Method 3
a main shaft motor for driving a main shaft
Implementation Method 4
a feed shaft motor for driving a feed shaft
Data Source
AI summary
A control device for a machine tool including a feed shaft motor for driving a feed shaft and a main shaft motor for driving a main shaft is provided with: a determination unit determining whether an operation of the feed shaft motor satisfies a predetermined determination condition; and an excitation command unit outputting an excitation current command to output excitation current larger than excitation current instructed by a master control unit to the main shaft motor, when the determination unit determines that the predetermined determination condition is satisfied.