Method and apparatus for testing a piezoelectric force sensor

• US 5,447,051 A
• Filed: 08/05/1993
• Issued: 09/05/1995
• Est. Priority Date: 08/05/1993
• Status: Expired due to Term

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Hanks, D. Mitchel, Metz, Larry S.
• Primary Examiner(s): RAEVIS, ROBERT R
• Application Number:
  US08/102,597
• Time in Patent Office: 761 Days
• Field of Search: 73/1 D, 73/2, 73/1 DV, 73/865.9, 73/DIG. 4, 180/282, 369/55
• US Class Current: 73/1.15
• CPC Class Codes: G01P 15/0922 of the bending or flexing mode type
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups

Abstract

A test system for a piezoelectric element per se or a piezoelectric element in a physical system, which is subject to forces which deform the piezoelectric element, couples an electrical pulse to the piezoelectric element sufficient to stress the element and induce mechanical ringing upon pulse removal. The ringing electrical signal developed by the piezoelectric element characterizes the functionality of the piezoelectric element. A response circuit which is responsive to the ringing electrical signal provides an electrical signal indicative of the functional condition of the piezoelectric element. The electrical signal is peak detected. The peak detected voltage is compared with a reference voltage to provide an indication of the functionality of the piezoelectric element.

Claims

1. A test system for testing a force transducer installed in a physical system, comprising:

a. a member to be controlled;

b. a control system coupled to said member for controlling said member;

c. a piezoelectric transducer in said physical system, said piezoelectric transducer having a piezoelectric element coupled in said control system for inserting the electrical output of said piezoelectric element into said control system to control said member;

d. means in said physical system for mechanically deforming said piezoelectric element to produce said electrical output;

e. a test signal circuit coupled to said piezoelectric element for momentarily applying the test signal and thereby electrically deforming said piezoelectric element, causing said piezoelectric element to mechanically ring upon removal of the test signal and produce a ringing electrical signal which characterizes the functional condition of said piezoelectric element;

f. a test response circuit responsive to said ringing electrical signal for determining the functionality of said piezoelectric element, and

g. a switch member controlled by said test signal circuit for disconnecting said control system from said piezoelectric element during testing of said piezoelectric element.

2. A test system for testing a force transducer installed in a physical system, comprising:

a. a member to be controlled;

b. a control system coupled to said member for controlling said member;

c. a piezoelectric transducer in said physical system, said piezoelectric transducer having a piezoelectric element coupled in said control system for inserting the electrical output of said piezoelectric element into said control system to control said member;

d. means in said physical system for mechanically deforming said piezoelectric element to produce said electrical output;

e. a test signal circuit coupled to said piezoelectric element for momentarily applying the test signal and thereby electrically deforming said piezoelectric element, causing said piezoelectric element to mechanically ring upon removal of the test signal and produce a ringing electrical signal which characterizes the functional condition of said piezoelectric element;

f. a test response circuit responsive to said ringing electrical signal for determining the functionality of said piezoelectric element, and

g. a first switch member coupled between said piezoelectric element and said test response circuit;

h. a second switch member coupled between said piezoelectric element and said control system;

i. a switch control circuit coupling said test signal circuit to said first switch member and to said second switch member for connecting said piezoelectric element to said test response circuit at said first switch member and disconnecting said piezoelectric element from said control system at said second switch member in response to testing of said piezoelectric element by said test signal circuit.

3. A test system for testing a force transducer installed in a physical system, comprising:

a. a member to be controlled;

b. a control system coupled to said member for controlling said member;

c. a piezoelectric transducer in said physical system, said piezoelectric transducer having a piezoelectric element coupled in said control system for inserting the electrical output of said piezoelectric element into said control system to control said member;

d. means in said physical system for mechanically deforming said piezoelectric element to produce said electrical output;

e. a test signal circuit coupled to said piezoelectric element for momentarily applying the test signal and thereby electrically deforming said piezoelectric element, causing said piezoelectric element to mechanically ring upon removal of the test signal and produce a ringing electrical signal which characterizes the functional condition of said piezoelectric element;

f. a test response circuit responsive to said ringing electrical signal for determining the functionality of said piezoelectric element, and

g. an amplifier having an input circuit and having an output circuit, said output circuit being coupled to said control system and said test response circuit, and

h. a switch member coupling said piezoelectric element to said input circuit of said amplifier and controlled by said test signal circuit for disconnecting said amplifier from said piezoelectric element for the duration of said momentary energization of said piezoelectric element by said test signal circuit.

4. A test system for testing a force transducer installed in a physical system, comprising:

a. a member to be controlled;

b. a control system coupled to said member for controlling said member;

c. a piezoelectric transducer in said physical system, said piezoelectric transducer having a piezoelectric element coupled in said control system for inserting the electrical output of said piezoelectric element into said control system to control said member;

d. means in said physical system for mechanically deforming said piezoelectric element to produce said electrical output;

e. a test signal circuit coupled to said piezoelectric element for momentarily applying the test signal and thereby electrically deforming said piezoelectric element, causing said piezoelectric element to mechanically ring upon removal of the test signal and produce a ringing electrical signal which characterizes the functional condition of said piezoelectric element;

f. a test response circuit responsive to said ringing electrical signal for determining the functionality of said piezoelectric element, and

g. an amplifier having an output circuit and an input circuit;

h. a normally open first switch member coupled between said output circuit and said test response circuit;

i. a normally closed second switch member coupled between said output circuit and said control system;

j. a normally closed third switch member coupled between said piezoelectric element and said input circuit, and

k. a switch control circuit coupling said test signal circuit to said first switch member, to said second switch member and to said third switch member for closing said first switch member and opening said second switch member for substantially the duration of said ringing signal and for opening said third switch member for the duration of said momentary energization of said of said piezoelectric element by said test signal circuit.

5. The test system according to claim 4, in which:

a. said amplifier has a bandwidth which is higher than the reciprocal of the mechanical damping time constant of the piezoelectric element.

6. The test system according to claim 4, in which:

a. said test signal circuit produces a test signal pulse;

b. said test system further comprises an electric pulse circuit responsive to said test signal pulse for producing an electrical pulse coupled to said piezoelectric element;

c. said switch control circuit comprises a timer circuit branch connected to said first switch member and to said second switch member and responsive to said test signal pulse for producing a switch control timing signal having a duration substantially the duration of said ringing electrical signal, and

d. said switch control circuit comprises a second branch coupling said test signal to said third switch member to open said third switch member for substantially the duration of said timing signal to isolate said amplifier from said electrical pulse.

7. A test system for testing a force transducer installed in a physical system, comprising:

a. a member to be controlled;

b. a control system coupled to said member for controlling said member;

c. a piezoelectric transducer in said physical system, said piezoelectric transducer having a piezoelectric element coupled in said control system for inserting the electrical output of said piezoelectric element into said control system to control said member;

d. means in said physical system for mechanically deforming said piezoelectric element to produce said electrical output;

e. a test signal circuit coupled to said piezoelectric element for momentarily applying the test signal and thereby electrically deforming said piezoelectric element, causing said piezoelectric element to mechanically ring upon removal of the test signal and produce a ringing electrical signal which characterizes the functional condition of said piezoelectric element;

f. a test response circuit responsive to said ringing electrical signal for determining the functionality of said piezoelectric element, and

g. said test response circuit comprises a reference electrical signal source for producing a reference electrical signal, and

h. said test response circuit comprises a peak detector for receiving said ringing electrical signal and a comparator for differentially comparing the electrical output of said peak detector with said reference electrical signal.

8. The test system according to claim 7, in which:

a. said reference signal has a value which is substantially the nominal peak value of said ringing electrical signal.

9. A method for testing the piezoelectric element of a piezoelectric transducer comprising the steps of:

a. subjecting the piezoelectric element of said transducer to a voltage to induce mechanical strain in said element;

b. removing said voltage to permit said element to mechanically ring and produce a ringing electrical signal;

c. examining said ringing electrical signal by comparing said ringing electrical signal with a reference electrical signal indicative of a desired functionality of said piezoelectric transducer, and

d. said reference signal being an empirically measured nominal peak value of voltage of the ringing electrical signal of a functional piezoelectric element.

10. An air bag system for protecting an occupant of a vehicle, comprising:

a. a deflated air bag on said vehicle;

b. an air supply on said vehicle;

c. a normally closed valve coupling said air supply to said air bag for inflating said air bag when said valve is opened;

d. a piezoelectric accelerometer on said vehicle to respond to components of acceleration acting longitudinally of said vehicle, at and above a predetermined level of acceleration

e. valve control means coupling said piezoelectric element to said valve to operate said valve to inflate said air bag in the presence of acceleration of said vehicle at and above said predetermined level of acceleration;

f. a switch on said vehicle;

g. a test circuit responsive to operation of said switch for coupling a voltage pulse to said piezoelectric element of said accelerometer to cause said piezoelectric element to mechanically ring and to produce a ringing electrical signal;

h. response circuit means coupled to said piezoelectric element to respond to said ringing electrical signal and provide a response indicative of the functionality of said piezoelectric element, and

i. means responsive to operation of said test circuit to test said piezoelectric element for disabling said valve control means to prevent operation of said valve during testing of said piezoelectric element.

11. A disk drive, comprising:

a. at least one rotatably mounted disk having a surface containing radially spaced tracks;

b. a motor for rotating said at least one disk at substantially constant speed;

c. a transducer for sensing tracks;

d. a movable actuator for moving said transducer to different radial locations with respect to the surface of said at least one disk;

e. an actuator motor for moving said movable actuator;

f. an actuator motor control system coupled to said actuator for moving said actuator to position said transducer at a selected track on said surface of said at least one disk;

g. a piezoelectric accelerometer on said disk drive responsive to acceleration of said disk drive which causes relative displacement between said transducer and said tracks, for additionally controlling said control system to oppose such relative displacement, said piezoelectric accelerometer having a force sensitive piezoelectric element;

h. a test system coupled to said piezoelectric element for momentarily energizing and thereby mechanically stressing and deforming said piezoelectric element causing it to mechanically ring upon termination of momentary energization, mechanical ringing of said piezoelectric element producing a ringing electrical signal which characterizes the functionality of said piezoelectric element, and

i. a response circuit coupled to said piezoelectric element for comparing a peak value of said ringing electric signal with a reference signal for obtaining a response representing the functionality of said piezoelectric element.