Machine Tool Spindle Control With Proportional Speed Fluctuation
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Solution Overview
Problem
Conventional methods for suppressing regenerative self-excited chatter vibration in machine tools are ineffective at higher rotation speeds due to a stable speed change rate, leading to unstable suppression effects.
Innovation Solution
A control device for a machine tool that includes a fluctuation command calculation unit to calculate a fluctuation command based on a speed command for the main spindle motor, and a speed control unit to control the rotation speed, ensuring the rotation speed of the main spindle motor periodically fluctuates with defined amplitude and frequency rates, maintaining a constant speed change rate regardless of the spindle speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the rotation speed of the main spindle is increased to improve productivity, then the productivity increases, but the speed change rate decreases and the suppression effect of chatter vibration becomes unstable
Solution Approach 1:
The invention changes the parameters of speed fluctuation from fixed absolute values to values that are proportions of the current rotation speed. Specifically, the fluctuation amplitude is set as a percentage (e.g., 5-20%) of the rotation speed, and the fluctuation frequency is set as a percentage (e.g., 0.1-10 Hz) of the rotation speed. This parameter transformation ensures that the speed change rate remains constant regardless of the absolute rotation speed, thereby maintaining stable chatter vibration suppression across different productivity levels.
2Device complexity
If fixed absolute values are used for speed fluctuation amplitude and frequency, then the control is simple, but the suppression effect deteriorates at higher rotation speeds
Solution Approach 1:
The invention transforms the control parameters from fixed absolute values to relative proportional values. The fluctuation amplitude is defined as a percentage of the current rotation speed (e.g., 5-20%), and the fluctuation frequency is defined as a percentage value (e.g., 0.1-10 Hz) that scales with rotation speed. This parameter change maintains control simplicity while ensuring effective suppression across varying rotation speeds.
3Reliability
If the rotation speed fluctuation amplitude is increased to improve chatter vibration suppression, then the suppression effect improves, but the machining precision may deteriorate due to excessive vibration
Solution Approach 1:
The invention optimizes the fluctuation amplitude as a controlled percentage (5-20%) of the rotation speed, which provides sufficient speed variation to suppress chatter vibration while preventing excessive amplitude that would degrade machining precision. This proportional parameter control balances suppression effectiveness with precision maintenance.
Solution Approach 2:
The invention applies a moderate fluctuation amplitude (5-20% of rotation speed) that is sufficient to disrupt the regenerative chatter mechanism but not so large as to cause excessive vibration affecting machining precision. This partial action approach achieves the minimum necessary fluctuation for suppression while avoiding over-fluctuation that would harm precision.
Data Source
AI summary
Provided is a control device for a machine tool capable of stably achieving an effect of suppressing regenerative self-excited chatter vibration. This control device for a machine tool includes a fluctuation command calculation unit configured to calculate a fluctuation command based on a speed command for a main spindle motor of the machine tool and a fluctuation condition for causing a rotation speed of the main spindle motor to periodically fluctuate, and a speed control unit configured to control the rotation speed of the main spindle motor based on the speed command and the fluctuation command. The fluctuation command calculation unit is configured to calculate the fluctuation command by calculating a frequency of the rotation speed that periodically fluctuates of the main spindle motor based on the rotation speed of the main spindle motor based on the speed command and a frequency rate that is the fluctuation condition.