CONVEYOR SPEED MONITOR

• US 3,780,297 A
• Filed: 10/04/1971
• Issued: 12/18/1973
• Est. Priority Date: 10/04/1971
• Status: Expired due to Term

• Current Assignee: Big Dutchman Cyclone Incorporated
• Original Assignee: Fred Geary
• Inventors: Geary, Fred
• Primary Examiner(s): Stolwein, Walter
• Application Number:
  US05/186,137
• Time in Patent Office: 806 Days
• Field of Search: 250/231,219FR,219DR,206,223R,223B,233
• US Class Current: 198/502.4
• CPC Class Codes: G01P 1/103 by comparing the value of the measured signal with one or several reference values in general G01R17/00
• CPC Class Codes: G01P 3/486 delivered by photo-electric detectors

Abstract

Light chopping means are coupled to a conveyor belt such that as the speed of the conveyor belt varies, a light path between a source of light and a photo-resistance cell is interrupted at a frequency directly related to the conveyor belt speed. The photo cell is coupled in an electrical circuit for detecting speed variations by detecting the resulting frequency variations of the light pulses. The electrical circuit provides an indicating signal when the speed of the conveyor belt reaches a predetermined level and also develops a control signal which can be employed for automatically regulating drive apparatus or other equipment associated with the conveyor system.

Claims

1. A speed monitor circuit comprising:

means for generating electrical signals whose frequency is directly related to the speed of a moving object, said generating means including a continuous source of light and light chopping means, said light chopping means being mechanically coupled to a moving object such that the rate of chopping of said light from said light source is directly related to the speed of said moving object, and a photoresistance cell whose resistance value varies when light is directed upon a light responsive surface thereof, said cell positioned to receive pulses of light developed by said light chopping means;

a direct voltage source;

means coupling said charge storage device to a direct voltage source to charge said device at a selectable rate, and coupling said photo-resistance cell to said source of voltage;

voltage responsive switch means including a control element coupled to said photo-resistance cell and responsive to signals therefrom to be activated each time a light pulse intercepts said photo-resistance cell thereby completing a conduction path, said switch means coupled to said charge storage device to discharge said device when the conduction path of said switch is completed; and

circuit means coupled to said charge storage device and actuated by predetermined voltage across the device to provide an output signal when the frequency of signals from said generating means falls below a predetermined value.

2. A circuit as defined in claim 1 wherein said means coupling said charge storage device to said voltage source includes a variable resistance to provide a selectable charging rate of current to said charge storage device.

3. A circuit as defined in claim 2 wherein said circuit means includes a second voltage responsive switch coupled to said charge storage device and responsive to the voltage across said charge storage device when the voltage across said charge storage device reaches said predetermined value to conduct.

4. An electrical circuit as defined in claim 3 wherein said voltage responsive switch comprises a discharge tube coupled in series with an impedance element, the combination coupled in parallel with said charge storage device such that a signal is developed across said impedance element when said discharge tube is activated.

5. An electrical circuit as defined in claim 4 wherein said circuit means includes a third voltage responsive switch having a control element coupled to said impedance element such that said third voltage responsive switch is activated by a signal developed across said impedance element.

6. A circuit as defined in claim 5 and further including:

a first output terminal coupled to said source of voltage, and a second output terminal coupled to said third voltage responsive switch such that when said third voltage responsive switch is activated, an output signal is developed across said first and said second output terminals.

7. In a conveyor having a moving conveyor belt, a conveyor speed monitor comprising:

means coupled to a conveyor for generating light pulses whose frequency is directly related to the speed of the conveyor belt;

a source of direct voltage;

means including switch means coupled across a resistor and having a calibration position in which said switch shorts out said resistor and an operating position in which said switch is open for coupling said direct voltage source to a capacitor for charging said capacitor at a first or second selected rate corresponding to calibration and operation of said speed monitor;

circuit means coupled to said generating means and responsive to said light pulses to provide a periodic discharge current path for said capacitor;

variable resistance means coupled from said switch means to said capacitor such that when said switch means is in the calibration position to short out said resistor, said variable resistor can be adjuSted to maintain the voltage developed across said capacitor below a predetermined level; and

detecting means coupled to said capacitor and responsive to said predetermined voltage level across said capacitor to develop an output signal when said capacitor is charged to said predetermined voltage level when the conveyor speed decreases below the desired speed and the time interval between the periodic discharging of said capacitor increases to permit said capacitor to be charged to said predetermined voltage.

8. A conveyor speed monitor as defined in claim 7 wherein said means for generating light pulses comprises a source of continuous light and chopping means for chopping light from said source into pulses, said chopping means being mechanically coupled to said conveyor belt such that the pulse frequency of the resulting chopped light is directly related to the speed of said conveyor belt.

9. A monitor as defined in claim 7 wherein said circuit means responsive to said light pulses to provide a periodic discharge current path includes a voltage responsive switch having a control element, light sensitive means for receiving light pulses from said light source, and means coupling said light sensitive means to said control element of said voltage responsive switch such that as a light pulse intercepts said light sensitive means, said voltage responsive switch is activated to conduct and said capacitor.

10. A monitor as defined in claim 7 wherein said detecting means includes a voltage responsive switch coupled to said capacitor whereby said voltage responsive switch is actuated when said capacitor voltage reaches said predetermined level, said second voltage responsive switch coupled in series with a source of voltage and an impedance such that a voltage is developed across said impedance when said voltage responsive switch is actuated.

11. A conveyor speed monitor as defined in claim 10 wherein said detection means further includes an additional voltage responsive switch having a control element coupled to said impedance, said additional voltage responsive switch coupled in series with indicator means, the combination coupled from a voltage source to ground.

12. A monitor as defined in claim 11 wherein there is further included a first output terminal coupled to a first terminal on said indicator means and a second terminal coupled to a second terminal on said indicator means such that an output signal is developed across said output terminals in the event said third voltage responsive switch is actuated.

13. For use in a conveyor system employing a movable conveyor belt, a conveyor belt speed monitor comprising:

a housing including a central opening for receiving a spool, a first aperture for receiving a light source, a second aperture spaced across said central opening from said first aperture for receiving a light responsive means, said housing including an additional aperture providing a light path from said first aperture to said second aperture;

a spool rotatably mounted within said central opening and including at least one aperture extending therethrough which aligns momentarily with said second and additional apertures to provide a momentary light path across said central opening as said spool is rotated;

a shaft coupled to said spool and extending from said housing, a wheel mounted to said shaft and external to said housing;

means for mounting said housing to said conveyor such that said wheel contacts the conveyor belt of said conveyor; and

circuit means coupled to said light responsive means for generating a control signal in response to light pulses received by said light responsive means.

14. A monitor as defined in claim 13 wherein said housing includes a bearing block assembly for rotatably holding said shaft.

15. A monitor as defined in claim 14 wherein said light responsive means comprises a photo resistance device.

16. The system as defined in claim 15 and further including a circuit board for supporting components of said circuit means including said photo resistance device, and a container supporting said circuit board and said housing relative to one another such that said photo resistance device extends into said second aperture of said housing.

17. A speed monitoring circuit comprising:

means for generating electrical signals whose frequency is directly related to the speed of a moving object;

a direct voltage source;

a charge storage device;

means coupling said charge storage device to said direct voltage source to charge said device continuously with current from said direct voltage source and at a selectable rate;

voltage responsive switch means including a control element coupled to said generating means and responsive to signals therefrom to be actuated to conduct, said switch means coupled to said charge storage device to discharge said device when the conduction path of said switch is completed; and

circuit means coupled to said charge storage device and actuated by a predetermined voltage developed across said device during the period of time between successive periods of non-conduction of said voltage responsive switch to provide an output signal when the frequency of signals from said generating means falls below a predetermined value, thereby allowing the voltage across said charge storage device to exceed a predetermined value.

18. A circuit as defined in claim 17 wherein said generating means includes a continuous source of light and light chopping means, said light chopping means being mechanically coupled to a moving object such that the rate of chopping of said light from said light source is directly related to the speed of said moving object.

19. A circuit as defined in claim 18 wherein said generating means further includes light intercepting means comprising a light responsive device positioned to receive pulses of light developed by said light chopping means.

20. A circuit as defined in claim 10 wherein said light responsive device comprises a photo-resistance cell whose resistance value varies when light is directed upon a light responsive surface thereof.