Tool damage prevention system

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Patent

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Details

36447417, 36447421, 3644743, 318565, G05B 194065

Patent

active

055879152

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a tool damage prevention system for preventing damage to a tool used in a numerically controlled machine tool.
2. Description of the Related Art
In machine tools, a tool can be damaged due to abnormal load applied thereto during a cutting operation, and therefore, various measures are taken to prevent such damage. Tool damage prevention methods primarily rely upon the detection of cutting load, and typical methods for detecting the cutting load are as follows: the like.
In the conventional method (1), however, a sensor must be arranged externally, and a control device for processing the sensor signal must be provided separately from a numerical control device, which leads to complicated arrangement and higher cost.
In the conventional method (2), since the current value of the spindle motor involves rotating load or acceleration/deceleration load of the spindle, the detection accuracy is poor and tool damage cannot be detected with accuracy.


SUMMARY OF THE INVENTION

The present invention was created in view of the above circumstances, and an object thereof is to provide a tool damage prevention system which can easily detect abnormal load with high accuracy to reliably prevent damage to a tool and which also can appropriately cope with abnormality when tool damage or the like has already occurred.
To achieve the above object, the present invention provides a tool damage prevention system for preventing damage to a tool used in a numerically controlled machine tool, comprising first disturbance torque estimating means for estimating a disturbance torque acting on a spindle for rotating the tool, second disturbance torque estimating means for estimating a disturbance torque acting on a feed shaft for controlling feed of the tool, comparing means for comparing a third estimated disturbance torque, obtained by combining the disturbance torques estimated by the first and second disturbance torque estimating means, with a preset reference torque, and deceleration/stop command means for outputting a command signal to decelerate or stop the feed of the tool or to change the tool in accordance with a result of the comparison by the comparing means.
The first and second disturbance torque estimating means estimate the disturbance torques acting on motors for driving the spindle and the feed shaft, respectively, by means of disturbance estimating observers; therefore, the loads applied to the spindle and the feed shaft, i.e., the load applied to the tool, can be estimated with accuracy. The comparing means obtains a composite disturbance torque by combining the disturbance torques acting on the spindle and the feed shaft, and compares the composite disturbance torque with the preset reference torque. The reference torque serves as an abnormal load detection level, and is set variably in accordance with factors such as tool types, hardness of workpieces, etc. Since the composite disturbance torque associated with both the spindle and the feed shaft is compared with the reference torque, the abnormal load detection level can be set so as to match the machining conditions then set.
In accordance with the result of the comparison by the comparing means, the deceleration/stop command means outputs a command signal to decelerate or stop the tool feed or to change the tool.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the principles of a tool damage prevention system according to the present invention;
FIG. 2 is a block diagram of the hardware of a numerical control device (CNC) for carrying out the tool damage prevention system of the present invention;
FIG. 3 is a block diagram showing an observer according to the present invention;
FIG. 4 is a flowchart showing a first example of a process executed by a PMC; and
FIG. 5 is a flowchart showing a second example of a process executed by the PMC.


DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment according to the present invention will be de

REFERENCES:
patent: 4745563 (1988-05-01), Kaku et al.
patent: 4943759 (1990-07-01), Sakamoto et al.
patent: 5091684 (1992-02-01), Iwashita
patent: 5115418 (1992-05-01), Shimada
patent: 5239248 (1993-08-01), Shimada et al.
patent: 5304906 (1994-04-01), Arita et al.

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