Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
1998-10-27
2001-12-11
Grant, William (Department: 2121)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S175000, C700S195000, C451S001000, C451S005000, C029S603090
Reexamination Certificate
active
06330488
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for controlling a machining process of a workpiece, particularly to a machining process control method in a height control process of a thinfilm magnetic head.
DESCRIPTION OF THE RELATED ART
In fabricating a thin-film magnetic head, a wafer with a large number of thin-film magnetic head elements is cut into rows so that a plurality of magnetic head sliders are sequentially coupled or aligned therein, and then each bar is processed for various works.
For example, control of a properties-determining height of a magnetoresistive effect (MR) head element (MR height) is executed by lapping an air bearing surface (ABS) of each bar. During the lapping of the ABS, the MR height is monitored by an electrical signal from a lapping control sensor called as a RLG (Resistance Lapping Guide) or ELG (Electric Lapping Guide) sensor to correct the bending of the bar and to control the stop position of the lapping, so as to obtain optimum properties of the MR head element. Such RLG machining process is described in for example U.S. Pat. No. 4,689,877.
However, according to the RLG machining process in which the machining amount is controlled based upon the detection signals from the RLG sensors, the following problem may occur. That is, if the detection signals include a signal having an abnormal value, the machining amount may become an extraordinal amount and therefore a workpiece such as a MR head element may be suffered excess lapping causing the good element to fail.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method for controlling a machining process of a workpiece, whereby correct machining control of the workpiece can be expected even if detected values of sensors include an abnormal value.
According to the present invention, a method for controlling a machining process of a workpiece includes a step of measuring amounts of machining of the workpiece by a plurality of sensors located at different positions on the workpiece, the sensors providing detection signals which represent the respective measured amounts, a step of removing the detection signal when the detection signal has an abnormal value which is extremely different in comparison with values of the other detection signals by using a smoothing method, and a step of controlling the machining of the workpiece depending upon the remaining detection signals from the sensors.
The machining of the workpiece is controlled depending upon the remaining detection signals after an abnormal value of the detection signal is removed by using the smoothing method. Therefore, the machining control can be always performed in accordance with the correct data causing decrease in magnetic head yields to prevent.
It is preferred that the removing step includes a step of calculating each rate of change between values of the detection signals of adjacent two sensors with respect to a distance between the adjacent two sensors, and a step of determining removal of the detection signal of each sensor depending upon a difference in the rates of change of the each sensor with respect to two sensors adjacent to the each sensor.
It is also preferred that the removing step further includes a step of omitting the detection signal with either the maximum value or the minimum value when a positive square root of sum of squares of differences of the rates of change exceeds a predetermined value.
It is preferred that the removing step includes a step of calculating an average value, a standard deviation and a regression line of values of the detection signals, a step of determining removal of the detection signal when a value of the detection signal is out of a range from the calculated regression line, the range being predetermined in accordance with a required precision for machining the workpiece, and a step of omitting the detection signal when the determining step determines the removal of the detection signal. The calculating step, the determining step and the omitting step may be repeated.
It is preferred that the controlling step includes a step of calculating a quaternary regression curve depending upon the remaining detection signals from the sensors, and a step of executing the machining control of the workpiece so that the calculated quaternary regression curve approaches to a straight line.
The workpiece may be a bar on which a plurality of thin-film magnetic head elements are aligned. This bar is obtained by cutting a wafer.
In this case, it is preferred that the controlling step includes a step of controlling a properties-determining height of the thin-film magnetic head elements on the bar by lapping an air bearing surface of the bar and by correcting bending of the bar, and that the values of the detection signals are machining amount values of the properties-determining height obtained from sensed signals of a plurality of sensors located at different positions on the bar.
The properties-determining height controlling step may include a step of measuring resistance values of the sensors, the resistance values being varied in accordance with the lapping and the correction of bending, and a step of calculating the machining amount values in accordance with the measured resistance values.
It is preferred that the controlling step includes a step of interpolating, when the removed detection signal is a signal from the sensor located nearest to one end of the bar, the values of the detection signals from the sensor adjacent to the end located sensor to provide a substitute detection signal. The properties-determining height control step is executed by using the remaining detection signals and the substitute detection signal.
The present invention can be used in various bar machining control using detection signals from sensors other than the properties-determining height control. Furthermore, the present invention can be applied to various machining control of workpieces other than the bar with a plurality of magnetic head elements.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.
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Kakegawa Noritsugu
Yoshida Tomoyuki
Arent Fox Kintner & Plotkin & Kahn, PLLC
Garland Steven R.
Grant William
TDK Corporation
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