Microwave Sensing

The present invention relates in general to microwave sensing and, more particularly, concerns novel apparatus and techniques for reliably counting or sensing objects. The apparatus is compact, requires very little input power, and is relatively easy to install and adjust.

There are numerous microwave sensing systems. It is an important object of this invention to provide an improved microwave sensing system which is readily and easily included as a component in control systems. To accomplish this goal, the invention senses a wide range of objects and is operable in an industrial environment.

According to the invention, there is circuitry to regulate and condition the input power, microwave transceiving means for transmitting microwave energy and receiving a portion of the transmitted energy reflected from an object to be sensed, amplifying and detecting means for providing a signal representative of an object to be sensed, and hold-off circuitry means for providing an output signal during a predetermined time interval after an object has been detected; the whole embodied in a compact, rugged unit requiring very little input power.

Numerous other features, objects and advantages of the invention will become apparent from the following specification when read in connection with the accompanying drawing in which:

FIG. 1 is a block diagram illustrating the logical arrangement of a system module according to the invention; and

FIGS. 2A and 2B are a schematic circuit diagram of a preferred embodiment of the invention.

With reference now to the drawing and more particularly FIG. 1 thereof, there is shown a block diagram illustrating the logical arrangement of a system according to the invention. A cavity controlled Gunn diode oscillator 13 is, cyclically pulsed on for 10 microseconds at a 100 Hz rate by the driver/detector circuitry 14 to provide microwave energy to the antenna 11 which illuminates an area where items or objects are to be sensed. The antenna 11 has a narrow radiation beam, typically within an angle of 22 degrees in one plane, usually horizontal, and 36 degrees in the perpendicular plane, usually vertical. Energy reflected from an object in this area captured by antenna 11 causes a change in the D.C. operating parameters of the Gunn oscillator. The driver/detector 14 samples the current drawn by the Gunn diode during each pulse, and any change in the reflected energy received by the oscillator (due, for example, to an object moving in or out of the beam of antenna 11) will, therefore, result in a change in the detected output. A.C. amplifier and filter 15 amplifies the detected signal by an amount determined by sensitivity control 23 which is accessible to the user. The threshold detector 16 provides an output pulse when the amplified signal exceeds a predetermined threshold. This threshold is adjusted automatically by the threshold circuitry to compensate for long-term changes in the Gunn oscillator due to environmental conditions. The output pulse of the threshold detector 16 then is lengthened by the re-triggerable hold-off delay circuitry 17 to eliminate multiple triggers from one object. This hold-off delay is controlled by adjustment 22 which is also accessible to the user. The output of the hold-off delay circuitry 17 is then amplified by output driver 12 to provide a signal at terminal 11 which is suitable for actuating a counter, control system or other devices. All the circuitry receives D.C. power from the power regulator and filter 21. The specific circuits are known in the art and are not a part of the invention. The invention is unique, however, in the application and interconnection of these circuits.

Referring to FIGS. 2A and 2B, there is shown a schematic circuit diagram of a preferred embodiment of the invention. This embodiment comprises integrated circuits U1-U4, transistors Q1-Q5 and associated circuit components. Since those skilled in the art will be able to build an actual working model of the invention with FIG. 2, FIG. 2 will only be briefly discussed. To the extend practical, circuit portions in FIG. 2 corresponding to blocks or other elements in FIG. 1 are identified by corresponding reference symbols.

The amplifier between pins 13, 14 and 16 of integrated circuit U2, the logical inverter between pins 8 and 9 of integrated circuit U3 and associated components comprise a square wave pulser that provides a 10 microsecond gating pulse every 10 milliseconds for enabling Gunn oscillator 13 and draws but 350 microamperes of current.

Resistor R9 comprises a current sensing resistor that develops a voltage indicative of the current drawn by power switch transistor Q3 when Gunn oscillator 13 is enabled to charge capacitor C7 through transistor Q4. Capacitor C7 functions as a sample and hold capacitor that provides a signal amplified by A.C. amplifier and filter 15 for delivery to threshold detector 16 to provide a signal for each item sensed through the logical inverter having terminals 7 and 12-14 of integrated circuit U3 that is delivered to hold-off circuitry 17 comprising a retriggerable monostable miltivibrator having an adjustable monostable duration controlled by the potentiometer connected to the anode of diode D3 to provide an output signal that is amplified by the output driver comprising transistor Q5.

The power regulator and filter 21 comprises integrated circuit U1 and associated components with the voltage divider network comprising resistor R3 and resistors providing D.C. potentials to the indicated pins of integrated circuits U2 and U4.

A feature of the invention resides in having the duty cycle significantly less than one percent, typically 0.1 percent. Pulsing occurs at an audio frequency, typically 100 Hz. A typical microwave frequency for Gunn oscillator 13 is 10.525 GHz.

The invention has a number of advantages. It senses both metallic and nonmetallic objects without actually touching the object. It can detect objects passing behind a screen or in a chute providing the screen or chute is nonmetallic. It is sufficiently sensitive to detect objects at a range as far as eight feet. The relatively narrow beam facilitates maintaining good resolution while having different beamwidths in orthogonal planes allows flexibility in optimizing the beamwidth for a given application. The invention is relatively unaffected by ambient contaminates, is relatively insensitive to noise, consumes very little power, operates over a wide temperature range, is of rugged construction and meets FCC regulations for RF emitting devices.

The invention may typically be used for parts counting, process control, container film monitoring, die ejection monitoring, obstruction warning systems, automatic door openers, intrusion alarms, limit switches or for counting vehicles or people.

The invention is designed to be incorporated into standard industrial enclosures with antenna 11 (which may be protected with an integral window) exposed to the environment. The unit may be designed to plug into standard circuit connectors.

There has been described novel apparatus and techniques for microwave sensing that uses a compact rugged reliable structure that may be readily incorporated into existing equipment for process control in the industrial environment. It is evident that those skilled in the art may now make numerous uses and modifications of and departures from the specific embodiments described herein without departing from the inventive concepts. Consequently, the invention is to be construed as embracing each and every novel feature and novel combination of features present in or possessed by the apparatus and techniques herein disclosed and limited solely by the spirit and scope of the appended claims.