Piezoelectric material detector

• US 5,438,230 A
• Filed: 12/06/1994
• Issued: 08/01/1995
• Est. Priority Date: 02/28/1994
• Status: Expired due to Fees

• Current Assignee: CTS Corporation
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Hall, Dale G.
• Primary Examiner(s): Dougherty, Thomas M.
• Application Number:
  US08/350,248
• Time in Patent Office: 238 Days
• Field of Search: 310/316-318, 310/330, 310/348, 340/617, 340/621
• US Class Current: 310/316.01
• CPC Class Codes: G01F 23/2965 Measuring attenuation of transmitted waves
• CPC Class Codes: G01F 23/2967 for discrete levels
• CPC Class Codes: G01F 23/2968 Transducers specially adapted for acoustic level indicators
• CPC Class Codes: G01N 2291/02836 Flow rate, liquid level
• CPC Class Codes: G01N 29/22 Details , e.g. general constructional or apparatus details
• CPC Class Codes: G01N 29/34 Generating the ultrasonic, sonic or infrasonic waves , e.g. electronic circuits specially adapted therefor
• CPC Class Codes: G01N 29/36 Detecting the response signal , e.g. electronic circuits specially adapted therefor
• CPC Class Codes: G03G 15/0856 Detection or control means for the developer level
• CPC Class Codes: G03G 15/086 the level being measured by electro-magnetic means

Abstract

An improved piezoelectric material detector. The material detector (10) has a transducer structure (12) adapted to provide a certain vibration activity. A reset circuit (30) is included to minimize the possibility of false readings. And, a driving circuit (52) and detecting circuit (68) are utilized to drive and sense the presence of a material.

Claims

1. An improved piezoelectric material detector, comprising:

(a) a transducer structure including a probe for providing a predetermined vibration activity;

(b) a reset circuit for minimizing false readings coupled to the transducer structure, the reset circuit including an oscillator which sweeps through a predetermined frequency range which includes a resonant frequency of the transducer, whereby when the resonant frequency is reached, the probe is vigorously vibrated to substantially clear caked or undesirable material in proximity to the probe;

(c) means for driving a transducer structure and detecting the presence of a material, coupled to the transducer structure; and

(d) a switching device for actuating the reset circuit and the driving and detecting means for a predetermined time, defining (i) a reset mode whereby the probe is vibrated vigorously to substantially clear caked or undesirable material in proximity of the probe, thereby minimizing the possibility of false or inaccurate detection of the presence of a material in proximity thereto, and (ii) a detecting mode whereby the presence or absence of the material is detected, respectively.

2. The material detector of claim 1, wherein the reset means includes an oscillator and voltage multiplier in series.

3. The material detector of claim 1, wherein the driving and detecting means includes an oscillator circuit.

4. The material detector of claim 1, wherein the driving and detecting means includes a detector circuit and a noise filter circuit in series, having an output coupled to an indicator.

5. The material detector of claim 1, wherein the transducer structure includes a probe, including:

a base having a substantially planer top surface;

a piezoelectric element mounted to the base and having a length extending from the top surface of the base; and

a plurality of substantially columnar protective posts, each having a length and a narrow cross-section for minimizing unwanted accumulation of material, and extending orthogonally from the planar top surface of the base, the posts being located at predetermined locations away from the piezoelectric element.

6. The material detector of claim 5, wherein the base and the protective posts are a molded plastic, and wherein the protective posts each have a length substantially equal to the length of the piezoelectric element.

7. An improved piezoelectric material detector, comprising:

(a) a transducer structure including a probe for providing a predetermined vibration activity;

(b) a reset circuit for minimizing false readings coupled to the transducer structure, the reset circuit including an oscillator which sweeps through a predetermined frequency range which includes a resonant frequency of the transducer, whereby when the resonant frequency is reached, the probe is vigorously vibrated to substantially clear caked or undesirable material in proximity to the probe;

(c) a driver circuit for driving a portion of the transducer structure to vibrate, coupled to the transducer structure;

(d) a detecting circuit for sensing the presence of a material, coupled to the transducer structure; and

(e) a switching device for actuating the reset circuit and the driver and detecting circuits for a predetermined time, defining (i) a reset mode whereby the probe is vibrated vigorously to substantially clear caked or undesirable material in proximity of the probe, thereby minimizing the possibility of false or inaccurate detection of the presence of a material in proximity to the probe, and (ii) a detecting mode whereby the presence or absence of the material is detected, respectively.

8. The material detector of claim 7, wherein the reset circuit includes an oscillator and voltage multiplier in series.

9. The material detector of claim 7, wherein the driver circuit includes an oscillator circuit.

10. The material detector of claim 7, wherein the detector circuit is coupled to a noise filter having an output coupled to an indicator.

11. The material detector of claim 7, wherein the transducer structure includes a probe, including:

a base having a substantially planar top surface,

a piezoelectric element mounted to the base and having a length extending from the top surface of the base; and

a plurality of substantially columnar protective posts, each having a length and narrow cross-section for minimizing unwanted accumulation of material, and extending orthogonally from the planar top surface of the base, the posts being located at predetermined locations away from the piezoelectric element.

12. The material detector of claim 11, wherein the base and the protective posts are a molded plastic, and wherein the protective posts each have a length substantially equal to the length of the piezoelectric element.