Tool life control method based on disturbance load torque of mot

Details Tool life control method based on disturbance load torque of mot Tool life control method based on disturbance load torque of mot

1994-11-15

1997-02-11

Chilcot, Richard

Measuring and testing

Dynamometers

Responsive to torque

73862191, 73104, 36447417, G06F 1500

Patent

active

056023472

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a tool life control method for detecting an expiration of the tool life of a machine tool, and more particularly, to a tool life control method based on a disturbance load estimation.
2. Description of the Related Art
When a machine tool is used for a long period of time, the tool progressively wears out, which deteriorates its cutting capability. It is necessary, therefore, to manage the tools in use so that an exhausted tool is replaced with a new tool. Conventionally, a tool life control is performed by observing the tool itself or a condition of the cut workpiece to see if the tool is worn out. Japanese Patent Laid-Open Publication No. 1-183338 is directed to a method of tool management in which the working hours of individual tools are integrated and when the integrated working hours of the tool reaches a predetermined lifetime, the tool is replaced.
In another conventional tool management method, the wear of the tool is measured by visually observing the tool or the condition of the cut workpiece. In this case, it depends on the experience and intuition of the person in charge of the tool management to determine the time for a tool change. This method lacks accuracy and has no objective criterion for the tool management. Moreover, according to the aforesaid tool management method in which the working hours of each tool is integrated and the tool is changed when the predetermined lifetime is reached by the integrated time, a tool may be replaced as an exhausted tool even if actual wear of the tool is so small that the tool is not yet exhausted. On the other hand, even though the actual tool wear is so large that the time for a tool change is reached, the tool may fail to be changed since the .lifetime is not reached by the working time. This method, therefore, involves the problems such as the deterioration of the machining accuracy and the waste of energy and time. Thus, this tool life control based on the working time is not an accurate and absolute method of tool life control.


SUMMARY OF THE INVENTION

The present invention provides a tool life control method in which the life of a tool is determined objectively and accurately in accordance with the estimated magnitude of the load acting on the tool.
A tool life control method for a tool according to the present invention comprises the steps of: executing predetermined machining on a predetermined workpiece using a machine tool; estimating, by a disturbance estimating observer, a disturbance load torque acting on at least one of motors for driving a spindle and a feed shaft during the execution of the machining; and comparing the estimated disturbance load torque with a set reference value and outputting a tool life termination signal when the estimated disturbance load torque reaches the set reference value. According to an aspect of the present invention, the disturbance estimating observer estimates the disturbance load torque based on a torque command value given as a command to the motor and the actual speed of the motor.
Since the cutting capability of the tool declines as the tool wears, the load acting on the tool varies depending on whether the machining is carried out using an unworn tool or a worn tool when the same machining is effected on the same workpiece. Thus, a load acting on the motor for driving a spindle or a feed shaft also varies depending on the degree of wear of the tool. According to the present invention, the load acting on the tool is estimated based on the estimation of the disturbance load torque acting on the motor by the disturbance estimating observer. The change in the estimated disturbance load torque corresponds to the change in the load acting on the tool and the progression of the wear of the tool. Thus, according to the present invention, if the value of the estimated disturbance load torque continues to change for a set period of time or longer while the predetermined workpiece is undergoing the predetermined machining,

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