Article presence sensor

• US 4,004,234 A
• Filed: 06/23/1975
• Issued: 01/18/1977
• Est. Priority Date: 06/23/1975
• Status: Expired due to Term

• Current Assignee: Owens-Illinois Glass Container, Inc. (O-I Glass, Inc.)
• Original Assignee: Owens-Illinois Incorporated (O-I Glass, Inc.)
• Inventors: Juvinall, John W.
• Primary Examiner(s): Miller, Jr., Stanley D.
• Assistant Examiner(s): Davis, R. P.
• Application Number:
  US05/589,633
• Time in Patent Office: 575 Days
• Field of Search: 328/5, 340/258 C, 331/65, 307/308, 307/235 K, 324/61 R
• US Class Current: 307/652
• CPC Class Codes: H03K 17/955 using a capacitive detector

Abstract

Apparatus for sensing the presence of an article. One end of a very high impedance resistor is held at a fixed voltage. The other end of the resistor is connected to a sensing element. When an article is placed close enough to the sensing element, a form of capacitive coupling to ground is created which causes a minute current flow through the resistor. This causes a small voltage drop across the resistor. The current and voltage difference are presented to a voltage follower which effectively amplifies the current. Sample and hold circuits furnish a signal which indicates the actual voltage level. A minimum level detector measures the voltage level with no article present. This level is compared with the sample and hold signal, and an article present signal is generated if the sample and hold signal is a pre-selected amount greater than the minimum level.

Claims

1. Apparatus for sensing the presence of an article which comprises, in combination:

a source of alternating current;

a high impedance resistor of at least 100 megohms value having one side thereof connected to said source of alternating current;

a metallic sensing element connected to the other side of said resistor;

a voltage follower circuit, connected to the same side of said resistor as said sensing element, for amplifying any signal generated as a result of an article being present before said sensing element;

electronic circuit means, connected to the output of said voltage follower circuit, for furnishing an output signal quantity representative of the total range of the signal from said voltage follower circuit;

said electronic circuit means including

first electronic means for sampling and holding the positive going peak of any electrical signal from said voltage follower;

second electronic means for sampling and holding the negative going peak of any electrical signal from said voltage follower; and

electronic difference means, connected to the output of both said first and second electronic means for sampling and holding, for generating an output signal quantity indicative of the peak to peak output value of said voltage follower;

electronic minimum level detection means connected to said electronic circuit means for detecting and holding the minimum value presented by said electronic circuit means during a pre-selected time period; and

electronic comparison means, connected to said minimum level detection means and to said electronic circuit means, for generating an output signal indicative of the presence of an article in response to said output signal from said electronic circuit means exceeding said minimum value by a pre-selected amount.

2. The apparatus of claim 1 which further includes electronic filter means connected in circuit between said electronic circuit means and said electronic comparison means for removing extraneous noise signal components.

3. The apparatus of claim 1 wherein the value of said high impedance resistor is 1000 megohms.

4. The apparatus of claim 1 which further includes:

a wave shaping circuit, connected to said source of alternating current, for generating a first output pulse in response to the positive peak of said alternating current and a second output pulse in response to the negative peak of said alternating current, said output pulses being transmitted to said electronic circuit means.

5. The apparatus of claim 4 wherein said first electronic means includes a trigger circuit response to said first output pulse to initiate said signal sampling.

6. The apparatus of claim 4 wherein said second electronic means includes a trigger circuit responsive to said second output pulse to initiate said signal sampling.

7. A method for detecting the presence of an article adjacent to a metallic sensing element which comprises the steps of:

furnishing an alternating current to a resistor having one side thereof connected to said sensing element;

inducing a current in said resistor as a result of a capacitive coupling of said article and said sensing element;

electronically generating a signal quantity representative of the peak to peak voltage across said resistor resulting from said induced current;

electronically sampling and holding a value representative of the minimum peak to peak voltage across said resistor during periods when no article is present;

electronically comparing said value representative of said minimum voltage and said signal quantity representative of the peak to peak voltage; and

generating an output signal indicating the presence of an article if said signal exceeds said value representative of said minimum voltage by a pre-selected amount.