US3565402A

US3565402A - Proximity sensing device

Info

Publication number: US3565402A
Application number: US842565A
Authority: US
Inventors: Ernest A Linke
Original assignee: Breeze Corp Inc
Current assignee: Breeze Corp Inc
Priority date: 1969-07-17
Filing date: 1969-07-17
Publication date: 1971-02-23
Anticipated expiration: 1988-02-23

Abstract

A magnetic sensing device is described which employs a rotating coil and core in a stationary limit position for sensing the proximity of a permanent magnet secured to the object to be sensed. The coil is connected to an amplifier circuit which may discriminate between frequency ranges and which is adapted to actuate a relay when the coil voltage is greater than a predetermined value.

Description

United States Patent Inventor Ernest A. Linlre [56] References Cited A I N 11 222 UNITED STATES PATENTS f July 1969 2,913,129 11/1959 Lindstrom 318/468 3,261,427 7/1966 Morris 317/123(P) Patented Feb. 23, 1971 Assignee i m Corporation Inc 3,487,280 12/1969 Santos 318/468 3,238,515 3/1966 Schrader etal 243/16 I Union, NJ.

Primary Examiner-Harvey C. l-lomsby Assistant ExaminerMerle F. Maffei PRQXIMITY SENSING DEVICE Attorney-Albert F. Kronman 10 Claims, 9 Drawing Figs. U.S.Cl 254/173, ABSTRACT: A magnetic sensing device is described which 254/168, 318/466, 324/34, 317/ 123, 340/258, employs a rotating coil and core in a stationary limit position 340/282, 254/186 for sensing the proximity of a permanent magnet secured to Int. Cl B66d l/48 the object to be sensed. The coil is connected to an amplifier held of Search 254/173, circuit which may discriminate between frequency ranges and 168; 243/16 (M); 318/466, 468; 324/34; 317/123 which is adapted to actuate a relay when the coil voltage is (P); 340/282 greater than a predetermined value.

M0704 I? l I 0 AL (on/ 7601 a X; r l ,34'6

BACKGROUND OF THE INVENTION Limit switches which turn off a motor or other circuit devices are common in the electrical art and have been employed for some time. However, when using a single limit switch on hoists or winches to stop the motion of articles having large inertia, the result is often unpredictable since a heavy moving object, such as a cable and hook plus the mass of the winch can overtravel when moving at high speed and move against the winch stop causing considerable damage. When moving at slow speeds, the hook may be left dangling. The use of several cam devices secured to the cable or winch gear train and operable to slow the cable speed in one or more steps before stopping it results in a satisfactory operation except when the end of the cable is damaged andthe hook is replaced. Before satisfactory operation can beeffected, the cams must be readjusted and tested.

The present invention employsa magnetic system which eliminates mechanical cams and settable limit switches. A permanent magnet is secured to the end of the cable, resting on top of the hook or other grappling device. The presence of the magnet is sensed by a rotating core and magnetic winding mounted just below the winch stop. The rotating winding is connected to one or more controlled rectifier or unijunction transistor trigger circuits which are adjusted to deenergize a relay whenever the generated voltage is equal to or more than a predetermined value. A first trigger circuit can be set to slow the cable motion to a known speed and then the second trigger circuit causes the cable to stop. In this manner the cable hook can be stopped at a position close to the limit position without any damage. 1

While the invention is described and illustrated in connection with a winch and cable termination, it can be adapted to many other mechanisms including rotating machinery, the tool support on a lathe, and the carriage on any type of metalcutting machine.

For a better understanding of the present invention, together with other details and features thereof, reference is made to the following description taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a side view of a motorized winch, a cable with a hook, and a sensing device surrounding the cable.

FIG. 2 is a cross-sectional view of the sensing device taken along a plane through the cable and showing the rotating coil, its core, and the coupling unit which moves it.

FIG. 3 is a cross-sectional view of the sensing device shown in FIG. 2 and taken along line 3-3 of that FIG.

FIG. 4 is a schematic diagram of connections of a circuit which can be used in connection with the sensing device. It includes a band-pass filter, an adjustable voltage divider, two controlled rectifier circuits, each terminated by a relay, and a motor.

FIG. 5 is a schematic diagram similar to FIG. 4, but showing only a single control circuit with a zener diode to establish the voltage level for opening the relay.

FIG. 6 is a cross-sectional view of a form of coupling which can be used to transfer the proximity signal from a rotating pickup device to a stationary magnetic system.

FIG. 7 is a portion of a sensing circuit similar to the one shown in FIG. 5 but using a unijunction transistor as the voltage-sensing means.

FIG. 8 is a bottom view of the stationary core shown in FIG. 6.

FIG. 9 is a complete proximity sensing circuit (shown in block) of a means for controlling a hydraulic lift.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, a winch 10 is shown having a reel I1 and a support 12 secured to a base 13. A cable 14 is wound on the reel 11 and is terminated by a hook 15. Just above the hook 15 a permanent bar magnet 16 is secured to the cable by any suitable means. A set screw may be used or a nonmagnetic clamping means may hold the magnet in place. The cable 14 passes through a hole in the base 13 and through the center of a sensing unit 17 which senses the proximity of the permanent magnet 16.

The reel 11 is turned by a motor 18 which is coupled to the reel 11 by a reduction gearing (not shown). Motor 18 is connected to a control unit 20 which may contain switches, resistors, and one or more manuallyoperated switch levers 21. Power is applied to the control unit 20 by power lines 22, connected to a source of electrical power. The sensing unit 17 is coupled to a second motor 23 which receives its power from the control unit 20 and turns a sensing winding and core within the unit. The details of the motor control unit 20 are not described here because the control unit is well known in the art and is not a novel part of the invention.

Referring now to FIGS. 2 and 3, the sensing unit 17 is enclosed in a nonmagnetic compartment 25 having upper and

lowerholes

26 and 27 for the passage of the cable 14. Inside the box is a nonmagnetic hollow cylindrical support 28 secured to the top box panel. The support 28 rotatably holds a bevel gear 30on a bearing and the gear is driven by a pinion 31, secured to a shaft 32 and coupled to the second motor 23. Gear 30 is secured to an insulator cylinder 33 which supports two slip rings 34 and two windings 35, each mounted on a core 36 having pole pieces 37. Two brushes 38 make contact with slip rings 34 and are connected to output leads 40 which run to the motor control unit 20. V

Referring now to FIG. 4, the circuit is shown which couples the windings 35 to the control unit 20. The circuit may be mounted in the box 25 or in the unit 20. The winding 35 is connected to a band pass filter 41 which eliminates many of the noise pulses which may be picked up by the sensing winding 35 from other sources. The band-pass filter is adjusted to pass alternating currents having a frequency equal to the frequency of the current generated by the winding 35 when turning at its normal speed. a

The band-pass filter is connected to a rectifier circuit which includes a diode 42 and a capacitor 43. This circuit applies direct current to a resistor 45 having a variable contact point 46. The contact point 46 is connected to two

zener diodes

44 and 44A and the firing electrodes of two solid state controlled rectifiers 47 and 48. Each of the rectifiers have their cathodes connected to the negative terminal of battery 39 and their anodes connected to the positive terminal in series with resistors 49 and 55. The

zener diodes

44 and 44A are connected in series with each firing electrode in order to fire the rectifiers at predetermined voltages. One zener diode 44 may have a negative breakdown voltage of 5 volts for slowing down the motor. The other zener diode 44A may have a breakdown voltage of 10 volts for stopping the motor.

The anodes of the rectifiers are also connected respectively to the base electrodes of amplifying

transistors

50 and 51 which have their output circuits connected directly to windings 56 and 57 of two

relays

60 and 63. The first relay includes contacts 61 which short circuit a resistor 62 when closed. The second relay includes contacts 64 which are connected in series with contacts 61 on relay 60 and one terminal of motor 18. The other terminal of the motor 18 is connected to the power source 39. One side of resistor 62 and one of the contacts 61 are connected to a switch 65 which connects the components to the positive side of the power source when closed.

When the circuit shown in FIG. 4 is in operation, both relay windings 56, 57, are provided with current because

transistors

50 and 51 are conductive. When main switch 65 is closed, current flows from battery 39 through the switch,

contacts

61 and 64, to the motor 18, operating it, and then back to the negative terminal of the battery.

When the permanent magnet 16 (FIG. 1) moves close to the core 37, an alternating voltage is induced in rotating winding 35. This voltage is rectified by diode 42 and applied to resistor 45 and both zener

diodes

44 and 44A. As the magnet '16 moves closer to core 37, more, voltage is generated until the voltage applied to zener diode 44 exceeds volts. The diode 44 then conducts, firing the controlled rectifier 47 and causing a considerable voltage drop across resistor 49. The is action renders transitor 50 nonconductive no current flows through winding 56, and contacts 61 are opened, thereby sending current through resistor 62 and slowing'down the motor 18. As the magnet 16 moves closer to core 37, the voltage at point 46 becomes still higher and, when it reaches volts, zener diode 44A is made conductive, rectifier 48 also conducts, lowering the voltage on the base of transistor 51,'cutting off current to winding 57, opening contacts 64, and stopping the motor 18.

it has been found that the current circuit can be adjusted to produce desired results when the magnet 16 moves to a position about 1 foot from the rotatingcoil 36 and the motor is slowed down. When the magnet reaches about 4 inches from rotating windows 35, the motor is stopped. These values may be changed by adjusting the variable contact 46.

FIG. 5 shows a simplified control circuit for stopping the motor at a desired distance fromits limit position. The adjustable contact has been eliminated as has also one relay and resistor 62. The operation is substantially the same. When the voltage generated by the rotating core 37 is greater than the breakdown voltage of zener diode-66, the controlled rectifier 69 passes current and the voltage drop across resistor 54 causes transistor 50 to become nonconductive. The current through winding 56 is reduced to zero and contacts 61 are opened, stopping the motor.

The mechanism shown in FIG. 2 employs two slip rings and two brushes to connect the generated AC voltage to the sensing circuit. The arrangement shown in FlGS. 6 and 8 eliminates the slip rings and uses a magnetic coupling 67 which includes a double rotating pair of windings 68 each on its core 70, 71. These cores 70, 71, rotate adjacent to a double annular magnetic stator 72 having an outer ridge 73 and an inner ridge 74.

Ridges

73 and 74, as shown in FIG. 8, are each formed in a full circle so that, as cores 70 and 71, revolve, the air gaps between the core remains constant. The outer and

inner ridges

73, 74 are connected by two

bridges

75, 76, each bridge supporting a secondary winding 77, 78. This type of coupling has been described and claimed in a pending Pat. application Ser No. 727,152 filed May 7, 1968 by the same applicant as in the present application.

The control circuit shown in FIG. 7 is an alternate method of sensing a desired voltage value. This circuit employs a unijunction transistor 80 having two bases and a single diode connection. One of the bases is connected to a dropping resistor 54 and the base electrode of a transistor amplifier 50. For small direct current inputs, the unijunction passes no current. When the applied voltage reaches a definite value, the device conducts and current flows through the diode connection to ground, thereby reducing the potential of the base electrode of transistor 50 and operating the connected relay.

FIG. 9 illustrates an applicationof the control circuit to a hydraulic lift which may be a elevator. The magnet 16 is mounted above the passenger cage 81 which is connected by a shaft 82 to a piston 83 in a hydrauliccasing 84. A valve 85 is opened when the piston and its load are to be raised. When the magnet 16 approaches the sensing core 37, the generated AC voltage is filtered by circuit 41, then rectified by circuit 86, sensed by circuit 87, and finally amplified and applied to a solenoid 88 to close the valve 85 and stop the fluid fiow. There are many other similar power-translating devices which could use this sensing arrangement. I

Having thus fully described the invention,

I claim: t I

1. In a load-handling system having cable means coupled between a reel and a movable object, power means for operat ing said reel to draw said object toward a limit position, the improvement which comprises: a rotating winding positioned adjacent to the limit position for detecting magnetic fields and for generating an alternating current voltage proportional to the intensity of the field; a permanent magnet secured to a portion of said movable object for generating a magnetic flux for detection by the rotating winding; a rectifier circuit connected to the rotating winding for producing direct current voltages derived from the rotating winding; a voltage responsive trigger circuit coupled to the rectifier circuit for producing an output pulse whenever the rectifier circuit produces a voltage above a predetermined value; and a control unit coupled between the output of the triggercircuit and said power means for disabling the power means and stopping the movable object.

2. A power system as claimed in claim 1 wherein said rotating winding is positioned on a ferromagnetic core.

3. A power system as claimed in claim 1 wherein a bandpass filter is coupled between the rotating winding and said rectifier circuit.

4. A power system as claimed in claim 1 wherein an amplifier is coupled between the rectifiercircuit and said trigger circuit for increasing the operating range of the system.

5. A power system as claimed in claim 1 wherein said cable passes through the center of the rotating winding.

6. A power system as claimed in claim 1 wherein the rotating winding is connected to slip rings and brushes for connection to the rectifier circuit.

7. A power system as claimed in claim 1 wherein said cable is wound on a reel and the reel is turned by an electric motor.

8. A power system as claimed in claim 1 wherein a second voltage responsive trigger circuitis coupled to the rectifier circuit in parallel with the first-mentioned trigger circuit, the second trigger circuit being set to operate at an input voltage which is less than the input operating voltage of the first trigger circuit, said second trigger circuit coupled to the control unit to reduce the speed of the cable to a predetermined value.

9. A power system as claimed in claim 1 wherein a relay is coupled between the output of said trigger circuit and the control unit.

10. A power system as claimed in claim 1, wherein an electric motor is coupled to said rotating winding for turning the winding at a predetermined speed.

Claims

1. In a load-handling system having cable means coupled between a reel and a movable object, power means for operating said reel to draw said object toward a limit position, the improvement which comprises: a rotating winding positioned adjacent to the limit position for detecting magnetic fields and for generating an alternating current voltage proportional to the intensity of the field; a permanent magnet secured to a portion of said movable object for generating a magnetic flux for detection by the rotating winding; a rectifier circuit connected to the rotating winding for producing direct current voltages derived from the rotating winding; a voltage responsive trigger circuit coupled to the rectifier circuit for producing an output pulse whenever the rectifier circuit produces a voltage above a predetermined value; and a control unit coupled between the output of the trigger circuit and said power means for disabling the power means and stopping the movable object.

3. A power system as claimed in claim 1 wherein a band-pass filter is coupled between the rotating winding and said rectifier circuit.

4. A power system as claimed in claim 1 wherein an amplifier is coupled between the rectifier circuit and said trigger circuit for increasing the operating range of the system.

8. A power system as claimed in claim 1 wherein a second voltage responsive trigger circuit is coupled to the rectifier circuit in parallel with the first-mentioned trigger circuit, the second trigger circuit being set to operate at an input voltage which is less than the input operating voltage of the first trigger circuit, said second trigger circuit coupled to the control unit to reduce the speed of the cable to a predetermined value.