Solid state limit switch and safety loop

Abstract

A solid state switch including a Hall effect sensor, a magnet that is detectable by the Hall effect sensor, and an inductor that can selectively interrupt the detection of the magnet so that the Hall effect sensor will only provide a predetermined output when the switch is operating properly and the magnet is detected. The solid state switch may be used in a safety loop having of plurality of solid state switches in series, where an input signal is provided to the first solid state switch is then provided by the output of each solid state switch to the inductor of the next switch if the switch has properly detected its associated magnet. If the final solid state switch outputs the same square wave signal that was input to the first switch, the safety loop can conclude that all switches are operating properly and have all properly detected the presence of the magnets.

Description

TITLESOLID STATE LIMIT SWITCH AND SAFETY LOOP BACKGROUND OF THE INVENTION1. FIELD OF THE INVENTION

[0001] The present disclosure relates to limit switches and, more particularly, to a solid state limit switch.2. DESCRIPTION OF THE RELATED ART

[0002] Limit switches are used in many areas to provide information about the state of equipment with moveable components, such as to confirm that passenger rail car doors are closed and locked. For example, mechanical limit switches having normally open and normally closed contacts that cannot be closed at the same time are connected in series and monitored to ensure that all of the doors of a rail car are closed and locked, and thus it is safe for a train to proceed. Unfortunately, mechanical limit switches are prone to failure over time, such as a result of contamination or oxidation inside the switch. When these switches are used to signal that a system is operating properly, such as by signaling that all rail car doors are closed and that it is safe for the train to proceed, a switch failure can cause unnecessary delays.

[0003] Conventional attempts to remedy the problems of mechanical switches include the use of solid state switches that operate without any moving parts. Solid state switches have not been successfully employed, however, because existing switch designs do not provide the necessary fail-safe conditions and therefore require complex circuits that users are often reluctant to adopt. Accordingly, there is a need in the art for a solid state switch design that can replace the functionality of a mechanical switch while maintaining the simplicity and reliability of the systems that employ the mechanical switch.BRIEF SUMMARY OF THE INVENTION

[0004] The present invention provides a solid state limit switch that can replace mechanical limit switches and be used to form reliable safety loops that will not provide false signals in the event of a failure. In a first embodiment, the present invention is solid state switch having a sensor configured to detect to a magnetic field having a predetermined orientation by outputting a signal, a magnet producing the magnetic field of the predetermined orientation and moveable between a proximate position where the magnet will be detected by the sensor and a spaced position where the magnet will not be detected by the sensor, an inductor interposed between the sensor and the magnet when the magnet is in the first position, and a pulse generator coupled to the inductor and configured to drive theinductor with a square wave signal that will selectively cancel the magnetic field produced by the magnet. The sensor may comprise a Hall effect sensor.

[0005] The present invention also provides an improved safety loop such as that used in connection with passenger rail car doors to signal that all doors have properly closed and are locked. More specifically, the door safety loop includes a first solid state switch having a first sensor configured to detect to a first magnetic field having a first predetermined orientation by outputting a first signal, a first magnet producing the first magnetic field of the first predetermined orientation and moveable between a first proximate position where the first magnet will be detected by the first sensor and a first spaced position where the first magnet will not be detected by the first sensor, and a first inductor interposed between the first sensor and the first magnet when the magnet is in the first proximate position. A second solid state switch having a second sensor configured to detect to a second magnetic field having a second predetermined orientation by outputting a second signal, a second magnet producing the second magnetic field of the second predetermined orientation and moveable between a second proximate position where the second magnet will be detected by the second sensor and a second spaced position where the second magnet will not be detected by the second sensor, and a second inductor interposed between the second sensor and the second magnet when the magnet is in the second proximate position is positioned downstream of the first sensor and has the second inductor driven by the first output of the first solid state switch. The sensor may comprise a Hall effect sensor and the inductor may be a drum core inductor. The pulse generator may be configured to drive the inductor to counteract a south pole of the magnet. The signal that is output from the sensor may be a square wave voltage that matches the square wave signal of the pulse generator when the magnet is in the proximate position. The signal output from the sensor may not be a square wave voltage that matches the square wave signal of the pulse generator when the magnet is the spaced position. The sensor and the inductor may be attached to a fixed location and the magnet may be coupled to a structure that is moveable into and out of proximity to the fixed location, such as a door frame and a door positioned in the door frame, respectively.A pulse generator is coupled to the first inductor and configured to drive the first inductor with an initial square wave signal that will selectively cancel the first magnetic field produced by the first magnet so that when the first magnet is in the first proximate position the first solid state switch will output a second square wave signal. Because the first output of the first solid state switch is coupled to the second inductor, any square wave signal output from the first solid state switch will selectively cancel the second magnetic field produced bythe second magnet when the second magnet is in the second proximate position so that second solid state switch will also output a square wave signal. The pulse generator may be coupled to the output of the second solid state switch and is configured to determine whether the square wave signal output from the second solid state switch matches the initial square wave signal. The first solid state switch may be associated with a first door controller unit of a first door and the second solid state switch associated with a second door controller unit of a second door. The pulse generator may be coupled to a door interlock relay. The door interlock relay may be configured to report that the first door and the second door are closed in response to the pulse generator determining that the third square wave signal matches the first square wave signal. The door interlock relay may be configured to report that the first door and the second door are not closed in response to the pulse generator determining that the third square wave signal does not match the first square wave signal. Thus, a number of solid state switches may be coupled in series so that the detection of the appropriate square wave signal by the pulse generator confirms that all solid state switches in the series have properly detected the presence of their associated magnets, thereby indicating - for example -that all doors are closed and locked so that the associated door interlock relay can report to the train that it is safe to proceed.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

[0006] The present invention will be more fully understood and appreciated by reading the following Detailed Description in conjunction with the accompanying drawings, in which:

[0007] FIG. 1 a schematic of a solid state switch according to the present invention.

[0008] FIG. 2 is a schematic of a safety loop employing a series of solid state switches according to the present invention.DETAILED DESCRIPTION OF THE INVENTION

[0009] Referring to the figures, wherein like numerals refer to like parts throughout, there is seen in FIG. 1, a solid state switch 10 that can be used detect and identify faults and that will provide a safe condition in the event of a failure of any of the components. Solid state switch 10 includes a magnet 12 and a sensor 14 that can detect the proximity of a specific magnetic field, such as a Hall effect sensor. As is known in the art, Hall effect sensors can be powered by a supply voltage and, depending on the presence or absence of a specific magnetic field, output the supply voltage. While a Hall effect sensor is preferred as sensor 14, other approaches that can be selectively switched by the presence of apredetermined magnetic field to output a corresponding voltage may be used such as tunneling magnetoresistance (TMR) sensors or Reed switches.

[0010] An inductor 16, such as a drum core inductor, is positioned between magnet 12 and sensor 14. Inductor 16 is driven by a pulse generator 18 to generate a magnetic field will counteract the magnetic field created by magnet 12 when magnet 12 is positioned proximately to sensor 14. FIG. 1 illustrates the use of a Hall sensor that responds to the south pole of magnet, so the inductor 16 would need to be driven oppositely to counteract the south pole of magnet 12. As seen in the top of FIG. 1, pulse generator 18 is configured to drive inductor 16 according to a square wave input so that the magnetic field generated by inductor 16 will selectively block the magnetic field of magnet 12 according to period of the square wave input. As a result, the presence of magnet 12 in proximity to sensor 14 will cause sensor 14 to output a square wave voltage that matches the square wave input to inductor 16 by pulse generator 18 as sensor 14 is only allowed to periodically detect the magnetic field of magnet 12. When magnet 12 is spaced apart from sensor 14, as seen in the bottom of FIG. 1, sensor 14 will not detect magnet 12 at all, and thus not provide a square wave output matching the input to inductor 16. If magnet 12 is again positioned proximately to inductor 16 and sensor 14, and inductor 16 is driven by the square wave input, sensor 14 will again provide a square wave output. Solid state switch 10 thus provides a square wave output in the present of magnet 12 that matches the square wave input used by pulse generator 18 to drive inductor 16.

[0011] In the event of any failure of sensor 14, inductor 16, or pulse generator 18, the output of sensor 14 will not be a square wave. For example, if sensor 14 fails by shorting out, it will no longer output a square wave. Even if inductor 16 is driven by a square wave input and thus is periodically blocking the magnetic field of magnet 12, the output from sensor 14 will be a constant voltage. If sensor 14 ceases to work, there will be no voltage output. If inductor 16 fails, sensor 14 will again either output a constant voltage or provide no output depending on whether magnet 12 is present or absent, and thus will not provide a square wave output. Finally, if pulse generator 18 has failed and is not providing the square wave input to inductor 16, sensor 14 will either provide a constant output if magnet 12 is present or provide no output if magnet 12 is absent, and thus will still not provide a square wave output. As a result, any output other than a square wave output from sensor 14 means that the magnet is not present (or that solid state switch 10 has failed) and a square wave output will always only indicate the magnet is in position. Solid state switch 10 may therefore be used in the same manner as a conventional mechanical limit switch, such as those used to confirm that adoor is closed or that a door is locked, and will never fail in a way that falsely provides a confirmation signal.

[0012] In one embodiment, solid state switch 10 may be used as a limit switch by positioning sensor 14 and inductor 16 in a fixed location, such as a door frame, with magnet 12 positioned on a component or structure that is moveable into and out of proximity to the fixed location, such as a door opening and closing (or vice versa). When the door is open, sensor 14 will not provide an output as magnet 12 is positioned removed from sensor 14. When the door closed, magnet 12 is brought into proximity to inductor 16 and sensor 14, and sensor 14 will output a square wave matching the square wave input to inductor 16 from pulse generator 18. If the output of sensor 14 does not match, then the door has not closed. The signal from solid state switch 10 may thus be used in the same manner as that received from a mechanical switch, e.g., to provide an indication that mechanical structure is in a particular state.

[0013] In another embodiment, multiple solid state switches 10 according to the present invention may be used in place of conventional mechanical limit switches, such as those used with conventional passenger car doors, to form a safety loop where multiple mechanical structures must all be in a particular state for subsequent operations to continue. For example, standard passenger cars may include two doors, with each door using two limit switches connected in series and associated with a door controller unit (DCU) to indicate that the door has closed and that the door has locked before the passenger car reports that the train is safe to move.

[0014] Referring to FIG. 2, solid state switches 10 according to the present invention may be employed to form a door safety loop 100 that can safely determine when all doors on the passenger car are closed and locked. For example, in a passenger car having two doors, two solid state switches 10 may be associated with a first DCU 110 of a first door, and two additional solid state switches 10 and 10 may be associated with a second DCU 110 of a second door to detect the position of the doors as being open or closed and the doors as being unlocked or locked. Each solid state switch 10 includes an input 20 coupled to inductor 16 and an output 22 coupled to the output of sensor 14. As seen in Table 1 below, the output of each solid state switch 10 depends on the presence of magnet 12 and the input to inductor 16:Table 1

[0015] Pulse generator 18 includes an output 24 coupled to the input 20 of the first solid state switch 10 and an input 26 coupled to the output 22 of the last solid state switch 10. Although FIG. 2 illustrates a loop containing a total of four solid state switches 10, it should be recognized that the loop may include any number of solid state switches 10. As explained above, pulse generator 18 is configured to continuously provide a square wave output, which in the example of FIG. 2 is provided to input 20 of first solid state switch 10. If magnet 12 of first solid state switch 10 is present, first solid state switch 10 will output a corresponding square wave via output 22 to input 20 of the next solid state switch 10. Thus, once magnet 12 associated with each solid state switch 10 in door safety loop 100 is present, e.g., all doors are closed and all doors are locked, the square wave signal generated by pulse generator 18 will propagate through every solid state switch 10 in door safety loop 100 and pulse generator 18 will receive a square wave at its input 26 that matches the square wave provided to input 20 of first solid state switch 10. Pulse generator 18 is thus configured to determine that it has received at its input 26 a square wave signal corresponding to the square wave signal provided at its output 24. The receipt of any other signal by pulse generator 18 indicates that not all doors are closed and locked or that there is a fault somewhere in the door safety loop. Door safety loop 100 could be implemented as a safety loop in any other situation where it is necessary to confirm the positioning of several moveable structures prior to taking further action, whether in a train or any other system or structure where mechanical limit switches may be used, such as safety interlocks on elevators, amusement rides, etc.

[0016] As seen in FIG. 2, pulse generator 18 may be installed proximately to the door interlock relay (DIR) 112 of a standard passenger car, which is usually located in the door relay panel of the passenger car. Pulse generator 18 may then trigger the closing of the door interlock relay (DIR) 112 that is used to signal to the trainline loop that all doors are closed and locked, thereby reporting to the trainline loop that the particular passenger car is safe to move. When each passenger car has similarly reported its doors closed and locked, the trainline loop is complete and the train can move.

[0017] As additionally seen in FIG. 2, each solid state switch 10 may also be coupled to each DCU 110 by a power supply input 28 and a monitoring output 30. DCU 110 may then monitor the status of solid state switch 10 to determine whether solid state switch 10 is defective, whether magnet 12 has been detected, whether a square wave has been received at input 20, or combinations thereof. DCU 110 may further be used to power solid state switch 10 and, by monitoring the current going to the switch, determine the statuses mentioned above.

[0018] Solid state switch 10, particularly when used as part of a safety loop such as door safety loop 100, offers many advantages over mechanical switches. For example, if a wire connecting the switches together is connected by accident to the passenger car body, to the battery return, or to the battery positive, no unsafe situation will be created as it might with a mechanical switch. The monitoring by DCU 110 will further allow for easier trouble shooting. For example, in case of a door loop failure, the location of the failure can be more easily located. As Hall effect sensors can cycle multiple billions of times, solid state switch 10 has a virtually unlimited lifespan and is unaffected by contamination or oxidation of the contact. Finally, solid state switch is completely fail-safe as any failure will cause the square wave pulse to stop.

[0019] The foregoing description of the present invention has been presented for purposes of illustration and description and is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiments were chosen and described in order to best explain the principles of one or more aspects of the invention and the practical application, and to enable others of ordinary skill in the art to understand one or more aspects of the present invention for various embodiments with various modifications as are suited to the particular use contemplated.

Claims

CLAIMSWhat is claimed is:

1. A solid state switch, comprising:a sensor configured to detect to a magnetic field having a predetermined orientation and to output a signal in response to detection of the magnetic field;a magnet producing the magnetic field of the predetermined orientation and moveable between a proximate position, where the magnet will be detected by the sensor, and a spaced position, where the magnet will not be detected by the sensor;an inductor interposed between the sensor and the magnet when the magnet is in the proximate position; anda pulse generator coupled to the inductor and configured to drive the inductor with a square wave signal that will selectively cancel the magnetic field produced by the magnet.

2. The solid state switch of claim 1, wherein the sensor comprises a Hall effect sensor.

3. The solid state switch of claim 1, wherein the inductor is a drum core inductor.

4. The solid state switch of claim 1, wherein the pulse generator is configured to drive the inductor to counteract a south pole of the magnet.

5. The solid state switch of claim 1, wherein the signal that is output from the sensor is a square wave voltage that matches the square wave signal of the pulse generator when the magnet is in the proximate position.

6. The solid state switch of claim 1, wherein the signal output from the sensor is not a square wave voltage that matches the square wave signal of the pulse generator when the magnet is the spaced position.

7. The solid state switch of claim 1, wherein the sensor and the inductor are attached to a fixed location and the magnet is coupled to a structure that is moveable into and out of proximity to the fixed location.

8. The solid state switch of claim 7, wherein the fixed location is a door frame and the structure is a door positioned in the door frame.

9. A door safety loop, comprising:a first solid state switch having a first sensor configured to detect to a first magnetic field having a first predetermined orientation by outputting a first signal, a first magnet producing the first magnetic field of the first predetermined orientation and moveable between a first proximate position where the first magnet will be detected by the first sensor and a first spaced position where the first magnet will not be detected by the first sensor, anda first inductor interposed between the first sensor and the first magnet when the first magnet is in the first proximate position;a second solid state switch having a second sensor configured to detect to a second magnetic field having a second predetermined orientation by outputting a second signal, a second magnet producing the second magnetic field of the second predetermined orientation and moveable between a second proximate position where the second magnet will be detected by the second sensor and a second spaced position where the second magnet will not be detected by the second sensor, and a second inductor interposed between the second sensor and the second magnet when the second magnet is in the second proximate position; anda pulse generator coupled to the first inductor and configured to drive the first inductor with a first square wave signal that will selectively cancel the first magnetic field produced by the first magnet so that when the first magnet is in the first proximate position the first sensor will output a second square wave signal; andwherein the first solid state switch includes a first output coupled to the second inductor so that the second square wave signal output from the first sensor will selectively cancel the second magnetic field produced by the second magnet when the second magnet is in the second proximate position and the second sensor will output a third square wave signal on a second output.

10. The door safety loop of claim 9, wherein the pulse generator is coupled to the second output and is configured to determine whether the third square wave signal matches the first square wave signal.

11. The door safety loop of claim 10, wherein the first solid state switch is associated with a first door controller unit of a first door.

12. The door safety loop of claim 11, wherein the second solid state switch is associated with a second door controller unit of a second door.

13. The door safety loop of claim 12, wherein the pulse generator is coupled to a door interlock relay.

14. The door safety loop of claim 13, wherein the door interlock relay is configured to report that the first door and the second door are closed in response to the pulse generator determining that the third square wave signal matches the first square wave signal.

15. The door safety loop of claim 14, wherein the door interlock relay is configured to report that the first door and the second door are not closed in response to thepulse generator determining that the third square wave signal does not match the first square wave signal.

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