Browse Prior Art Database

Ultra Precise Contact Sensor

IP.com Disclosure Number: IPCOM000041139D
Original Publication Date: 1987-Sep-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Jefferson, CM: AUTHOR

Abstract

A highly sensitive method and apparatus is described to determine precisely the instant at which two surfaces touch.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 71% of the total text.

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Ultra Precise Contact Sensor

A highly sensitive method and apparatus is described to determine precisely the instant at which two surfaces touch.

The apparatus comprises a force transducer 1 which is electrically insulated from a dither stack of piezoelectric material 2, a charge amplifier 3 which receives the output signal from force transducer 1, and a lock-in amplifier 4. The reference output signal on line 5 from lock-in amplifier 4 is used to driver amplifier 6 which provides the electrical drive signal to the stack of piezoelectric material 2.

The object 7, whose contact is to be determined, is fixed to the force transducer 1. The reference output of the lock-in amplifier 4 is coupled to drive the stack of piezoelectric material 2 and thereby dither the spacing h between the object 7 and movable surface 8 in a sinusoidal fashion. The force on object 7 is proportional to the dither frequency, w, squared in accordance with Newton's Law F=ma.

The amplitude of the force at frequency w is measured with the lock-in amplifier 4 by using the charge variation across the force transducer 1. If no contact exists between the two surfaces, then the R.M.S. magnitude of the resulting force is essentially constant, regardless of h, and the output of the lock- in amplifier 4 may be offset to zero. However, when two surfaces are brought sufficiently close so that object A touches surface B for some part of the oscillation of h, then the force will increase enormously. A sket...