Optical interruption sensor with opposed light emitting diodes

• US 8,981,280 B2
• Filed: 06/17/2010
• Issued: 03/17/2015
• Est. Priority Date: 08/03/2009
• Status: Active Grant

• Current Assignee: Illinois Tool Works Inc.
• Original Assignee: Illinois Tool Works Inc.
• Inventors: Larson, Eric K., Webster, Matthew C., Kang, Jian Hong, Grimes, Matthew J.
• Primary Examiner(s): LEE, JOHN R
• Application Number:
  US13/388,505
• Publication Number:
  US 20120138777A1
• Time in Patent Office: 1,734 Days
• Field of Search: 250/221, 250/222.1, 250/239, 250/214.A, 250/214.SW, 250/231.1, 250/231.13, 250/213.14, 250/232, 250/233, 250/231.14
• US Class Current: 250/221
• CPC Class Codes: G01D 5/2448 Correction of gain, threshold, offset or phase control
• CPC Class Codes: G01J 1/18 using comparison with a reference electric value
• CPC Class Codes: H01L 31/167 the light sources and the devices sensitive to radiation all being semiconductor devices characterised by potential barriers

Abstract

An optical-interrupter provides a mechanically integrated electric light source and electric light sensor positioned across a gap to transmit a light beam across the gap that may be interrupted with an opaque vane. The optical-interrupter uses conventional LEDs for both the light source and a light receiver. An integrated circuit comparator may be used to provide an adjustable threshold for the determination of whether the light beam is blocked.

Claims

1. A photosensor-photodetector assembly comprising:

a support defining an unobstructed light path through a gap from a first to a second position;

electrical terminals adapted to receive a direct current supply voltage and ground voltage for the photosensor-photodetector assembly and to provide an electrical output from the photosensor-photodetector assembly;

a solid-state light transmitter and solid-state light receiver attached to the support in the first and second positions so that light from the solid-state light transmitter may be received by the solid-state light receiver, the gap sized to permit an optical blocking element to pass into and out of the gap to block the light from the solid-state light transmitter to the solid-state light receiver;

a biasing circuit providing an electrical bias to the solid-state light transmitter and an electrical bias to the solid-state light receiver, when a direct current supply voltage and ground voltage are received by the electrical terminals;

detection circuitry including a threshold detector connected to the solid-state light receiver to compare a signal from the solid-state light receiver to a threshold signal to provide the electrical output;

wherein the threshold signal varies with the supply voltage to compensate for changes in the illumination of the solid-state light transmitter with changes in supply voltage; and

wherein the solid-state light transmitter and solid-state light receiver are both light emitting diodes; and

wherein a substantially continuous electrical bias that is a substantially proportional function of the supply voltage is applied to the solid-state light transmitter.

2. The photosensor-photodetector assembly of claim 1 wherein the light emitting diodes are selected to produce light of substantially identical light frequency when operated as light emitters.

3. The photosensor-photodetector assembly of claim 2 wherein the light emitting diodes emit visible light.

4. The photosensor-photodetector assembly of claim 3 wherein the light emitting diodes emit red light.

5. The photosensor-photodetector assembly of claim 2 wherein the light emitting diodes are substantially identical.

6. The photosensor-photodetector assembly of claim 1 wherein the light emitting diodes are constructed using direct band gap semiconductor materials forming a PN junction held within a housing as supported on an opaque substrate having a light transparent portion permitting light to pass along an axis to and from the PN junction.

7. The photosensor-photodetector assembly of claim 6 wherein an N-doped semiconductor of the PN junction abuts the opaque substrate.

8. The photosensor-photodetector assembly of claim 1 wherein the first and second positions are separated by less than three inches.

9. The photosensor-photodetector assembly of claim 1 wherein the detection circuitry connected to the solid-state light receiver provides a two-state electrical output having a first state when the solid-state light receiver receives a first intensity of light provided by unobstructed light from the solid-state light transmitter as biased by the biasing circuitry and having a second state when the solid-state light receiver receives a second intensity of light less than the first intensity of light.

10. The photosensor-photodetector assembly of claim 9 wherein the detection circuitry includes a comparator and wherein the comparator receives at one input an electrical signal from the solid-state light receiver having first and second values for the first and second intensities of light and the comparator receives at another input the threshold signal having a value between the first and second values.

11. The photosensor-photodetector assembly of claim 10 wherein the threshold signal and the electrical bias of the biasing circuit are each a function of a supply voltage to the photosensor-photodetector assembly.

12. The photosensor-photodetector assembly of claim 11 wherein the comparator is an integrated circuit differential amplifier.

13. The photosensor-photodetector assembly of claim 11 wherein the comparator provides an open collector output.

14. The photosensor-photodetector assembly of claim 1 wherein the support is a flexible printed circuit board held within a housing bending the flexible printed circuit board into a U-shape with the first and second positions located at ends of the U-shape.

15. The photosensor-photodetector assembly of claim 1 wherein the support is a rigid planar printed circuit board cut into a U-shape with the first and second positions located at ends of the U-shape.

16. The photosensor-photodetector assembly of claim 15 wherein the light emitting diodes provide a maximum light emitting direction parallel to a mounting surface of the light emitting diode abutting the support surface.

19. The photosensor-photodetector assembly of claim 1 wherein the biasing circuit includes a filter capacitor stabilizing its output voltage.

17. A photosensor-photodetector assembly comprising:

a movable light opaque vane;

a housing defining a light path through an open space from a first to a second position, the open space sized to permit movement of the vane into the open space in a first state and out of the open space in a second state;

electrical terminals adapted to receive a direct current supply voltage and ground voltage for the photosensor-photodetector assembly and to provide an electrical output from the photosensor-photodetector assembly;

a light source and light detector fixed with respect to the housing at respective first and second positions so that light from the light source may be received by the light receiver across the open space in the first state and blocked from the light receiver in the second state;

a biasing circuit providing an electrical bias to the light source and an electrical bias to the light detector, when a direct current supply voltage and ground voltage are received by the electrical terminals;

detection circuitry including a threshold detector connected to the light source to compare a signal from the light detector to a threshold signal to provide the electrical output;

wherein the threshold signal varies with the supply voltage to compensate for changes in the illumination of the solid-state light transmitter with changes in supply voltage; and

wherein both the light source and light detector are light emitting diodes designed to emit light of a same frequency when biased for light emission, the light emitting diodes having direct band open space semiconductor materials forming a PN junction held within a case and supported on an opaque substrate, the case having a non-opaque portion permitting light to pass into and out of the housing; and

wherein a substantially continuous electrical bias that is a substantially proportional function of the supply voltage is applied to the solid-state light source.

18. The photosensor-photodetector assembly of claim 17 wherein an N-doped semiconductor of the PN junction abuts the opaque substrate over an entire face of the N-doped semiconductor.