Self-calibrating dimension gauge

• US 3,986,109 A
• Filed: 01/29/1975
• Issued: 10/12/1976
• Est. Priority Date: 01/29/1975
• Status: Expired due to Term

• Current Assignee: ADE Corporation (KLA Corporation)
• Original Assignee: ADE Corporation (KLA Corporation)
• Inventors: Poduje, Noel S.
• Primary Examiner(s): Krawczewicz, Stanley T.
• Application Number:
  US05/545,111
• Time in Patent Office: 622 Days
• Field of Search: 324/61 R, 324/60 C, 324/60 R, 324/61 P, 324/DIG. 1, 317/246
• US Class Current: 324/662
• CPC Class Codes: G01B 7/023 for measuring distance between sensor and object G01B7/082 and G01B7/102 take precedence
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24

Abstract

A self-calibration system for use with a dimension-measuring probe. The self-calibration system includes a probe fixture which permits alternative orientation of the probe toward the work piece being gauged, or toward a readily available reference such as free space and a dimension reference typically of virtual infinite size. A closed loop feedback circuit is provided to develop a compensating signal for combination with the probe output to yield a dimension representing signal. The compensating signal is automatically set with the probe oriented toward the reference dimension to cause the dimension representing signal to correspond to a known value. Thereafter, the compensating signal is held constant and gauging of work piece dimensions can continue with system errors eliminated by the compensating signal.

Claims

1. A system for compensating the output of a dimension gauging probe including:

a dimension gauging probe;

means for orienting said probe and having first and second states, the first state orienting said probe toward a work object and the second state orienting said probe toward a reference dimension;

means for energizing said probe to provide a probe output signal representative of a dimension gauged thereby;

means for varying the value of the probe output signal in response to a control signal;

means for developing said control signal to provide a predetermined value corresponding to said reference dimension in the varied probe output signal in the second state of said orienting means and for maintaining said control signal in the first state of said orienting means thereby to provide compensation in the varied probe output signal.

2. In a dimension-gauging system having a dimension-responsive probe which provides an output signal representative of a dimension within a range of dimensions related to a work object, the improvement for providing a compensation in the output signal for system errors comprising:

means responsive to said output signal and a compensation signal for providing a composite signal representative of the algebraic combination of said output signal with said compensation signal;

means for selectively orienting the probe to point toward or away from the work object, the orientation away from the work object corresponding to a gauged dimension of extreme size larger than any dimension within said range of dimensions;

means for providing a reference signal corresponding to the composite signal for a gauged dimension of said extreme size;

means responsive to the reference signal and the composite signal for providing a difference signal representing the greatly amplified difference between the reference signal and the composite signal;

storing means having first and second states and operative in the first state for generating a signal representative of the difference signal and in the second state for storing the signal representative of the difference signal when the probe is oriented away from the work object;

means responsive to the stored signal for providing said compensation signal;

means for providing an output indicative of dimension in response to said composite signal.

3. In a dimension-gauging system a dimension-gauging probe which provides an output signal representative of a dimension associated with a work object, the improvement for providing a compensation in the output signal for system errors comprising:

means for generating a reference signal;

a closed loop circuit including a negative feedback path for a feedback signal and having;

a first input responsive to the output signal of said probe and algebraically combining it with said feedback signal;

a second input responsive to said reference signal and algebraically combining it with said feedback signal;

means for selectively interrupting the feedback path;

means in the feedback path beyond said interrupting means for storing said feedback signal;

means fixturing said probe for orientation away from said work object to cause said dimension to greatly increase beyond the range of normally gauged dimensions and intended for operation to direct the probe away from the work object simultaneously with no interruption in the feedback path and to direct the probe toward said work object after interruption in the feedback path.

4. In a dimension-gauging system having a dimension-responsive probe which provides an output signal representative of a dimension associated with a work object, the improvement for providing a compensation in the output signal for system errors comprising:

means for selectively orienting the probe to point toward or away from the work object;

means responsive to the probe output signal and a compensation signal for providing a composite signal representative of the algebraic combination of said probe output signal and said compensation signal and indicative of the measured dimension;

means responsive to the composite signal for generating a signal representing the difference between said composite signal and a reference signal;

means intended for activation when the probe is oriented away from the work surface corresponding to a gauged dimension of virtual infinite size for storing the signal representative of the difference in an activated state thereof;

means responsive to the signal stored during activation of said storing means for generating said compensation signal.

5. The system according to claim 4 wherein the means responsive to the probe signal and compensation signal includes a summing amplifier.

6. The system according to claim 4 wherein said reference signal is at ground potential and a further reference signal is provided for application to the composite signal providing means to provide said composite signal at the level of the first-mentioned reference signal when said probe is oriented away from the work object.

7. The system according to claim 4 wherein the means for generating the difference signal includes a high gain differential amplifier.

8. The system according to claim 4 wherein the means for storing a signal representative of the difference signal includes a switch and a slowly discharging capacitor to which the difference signal is applied when the switch is in a first state and from which the difference signal is isolated when the switch is in a second state.

9. The system according to claim 4 wherein the means responsive to the signal stored during activation of said storing means includes an amplifier imparting to the storing means a time constant which is long compared to the time interval of intended use between calibrations for said system.

10. A method for providing error compensation in a dimension-gauging system having a dimension-responsive probe which provides an output signal representative of a dimension associated with a work object comprising the steps of:

combining said probe output signal with a compensation signal to provide a composite signal representative of the algebraic combination of said output signal and said compensation signal,

developing the compensation signal from a signal stored in a storing means;

orienting the probe away from the work object toward a dimension of increased size;

storing a signal in said signal storing means representative of a signal amplitude which causes the composite signal to have a predetermined value for the dimension of increased size;

reorienting the probe toward the work object whereby dimension measurements may proceed with system errors corrected in the composite signal; and

providing an output indicative of dimension in response to said composite signal.

11. The method of claim 10 wherein the step of storing a signal includes the steps of applying a reference signal in said composite signal to produce the predetermined value therefor.

12. A dimension-gauging system for use over a range of dimensions comprising:

a probe including;

a first electrode having a capacitance associated therewith which varies in response to the dimensions being gauged;

a second electrode having a capacitance associated therewith which is generally independent of the dimension being gauged;

means for applying electrical excitation to the first and second electrodes;

means responsive to the excitation applied to said first and second electrodes for providing an output signal representative of the difference in the capacitances associated with said first and second electrodes;

a third electrode positioned to increase the capacitance associated with said second electrode whereby said output signal has a zero signal level corresponding to a predetermined finite dimension; and

compensation circuitry having;

means for selectively orienting said probe toward a reference dimension;

means for generating a compensation offset in said output signal; and

means for establishing said compensation offset in said output signal when said probe is oriented toward said reference dimension to produce a predetermined signal level in the output signal.