GB2348962A

GB2348962A - A proximity switch for detecting an object at two locations

Info

Publication number: GB2348962A
Application number: GB0009243A
Authority: GB
Inventors: Norman Victor Wheat
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-04-14
Filing date: 2000-04-14
Publication date: 2000-10-18
Also published as: GB0009243D0; GB9908365D0

Abstract

A proximity switch device 4 is fitted to a first item at location 8 for detecting the relative movement of a second item 2. The proximity switch device 4 comprises a sensor capable of sensing the presence of the second item at at least two positions 9, 11, and triggering a change in the condition of the device. The sensor may comprise a magnetic coil or core for generating a magnetic field and two sensor circuits. The switching positions may be adjusted by tuning the point of resonance of the sensor circuits, using a screw head mechanism or a microprocessor.

Description

Proximity Switch The invention to which this application relates is a proximity switch which is a term given to describe a range of devices which are used to provide an indication of the proximity of one item to another and especially, when an item is moving with respect to the other, to indicate when the item comes close to or moves away from the other item.

There are various forms of proximity switches such as inductive switches, capacitive switches but in general the switch is mounted on the item which is in a fixed position. Thus, in use, if the moving item comes toward the switch it reaches a point known as the switching point which causes an electrical signal to be generated in the switch. If the item moves away from the switch then, when it reaches a distance known as hysteresis, the electrical signal at the switch is turned off.

It will therefore be appreciated that there are a number of possible uses for proximity switches and the same can be arrange to operate in a number of ways. For example, if it is desired to indicate when the moving item has moved too close to the fixed item the switch can be arrange so as to provide the indication by causing a change in the electrical signal which, in some instances may be from the signal changing from off to on when the item moves towards the fixed item and past the switching point, or vice versa. If the desire is to detect when the moving item moves too far away from the fixed item the change in electrical signal occurs when the device moves past the point of hysterisis and again the electrical signal can be arrange to move from on to off or vice versa. It will therefore be appreciated that it is the change in condition of the electrical signal which provides the required indication to allow detection of position of the moving item at switching locations.

When it is required to measure two parameters such as the desired closest and furthest distances for the movable item from the fixed item, it is currently necessary to use two proximity switches, one set to provide a change in electrical signal when the moving item passes a closest switching point and the other to provide a change in electrical signal when the moving item passes the furthest hysteresis or switching point. It is then possible for the electrical signals to be processed and one signal generated for subsequent use.

The use of two proximity switches to detect furthest and nearest points is costly in that double the equipment is required and can be more susceptible to failure in that with two switches being used there is an increased risk of failure, which cannot always be easily detected in certain operating conditions of the switches, such as when the switch is normally off, and there is an increased risk of one of the switches being moved out of position.

The aim of the present invention is to provide a proximity switch which can be used and controlled to provide an indication of the position of a moving item relative to another item at two locations such as to provide an indication when the item is positioned between desired furthest and nearest locations.

A further aim is to provide the switch in a manner which allows failure of the same to be more clearly detectable.

In a first aspect of the invention there is provided a proximity switch device fitted to a first item to detect movement of a second item with respect to the proximity switch and wherein said proximity switch comprises a sensor and is capable of sensing the position of said first item at at least two spaced locations, with respect to the proximity switch.

Typically the first item is held in a fixed position so that the proximity switch effectively provides an indication of the position of the second item with respect to the first item.

In one embodiment the proximity switch device is provided with or connecte to any or any combination of visual and/or audio indication means which indicate the condition of the same and changes as the moving item moves through the first and/or second locations.

In one embodiment a magnetic coil is provided which can generate a wide-ranging magnetic field, which allows the switch to sense positions around the sensor. Alternatively, a magnetic core is provided which can generate a unidirectional magnetic field to sense positions at the sensor.

In one embodiment the proximity switch device can be controlled to change condition when the second item passes one location.

In one embodiment the device inclues a first electronic circuit which is used to sense and cause a change in condition as the second item moves past a first location, and a second electronic circuit which is used to sense and cause a change in condition as the second item moves past a second location.

In one embodiment a screw head is used to adjust the position of the first switching location and/or the at least second switching location.

In a further embodiment a microprocessor is provided to adjust the position of the first switching location and/or the at least second switching location.

Visual and/or audio indication means can be provided to indicate the first switching location, the at least second switching location and/or the position of the second item. The visual indication means can include LED's, LCD's and/or display screen on which bar graphs and the like can be shown.

According to a second aspect of the present invention there is provided a proximity switch device fitted to a first item to detect movement of a second item with respect to the proximity switch and wherein said proximity switch comprises a first electronic circuit to sense and cause a change in condition as the second item moves past a first location, and at least a second electronic circuit is provided to sense and cause a change in condition as the second item moves past at least a second location.

Specific embodiments of the invention are now described with reference to the accompanying drawings wherein ; Figure 1 illustrates one possible use of a proximity switch device according to the invention ; Figures 2 and 3 illustrate cross sectional views through a proximity switch device in one embodiment ; Figures 4 and 5 illustrate cross sectional views through a proximity switch device in a second embodiment ; Figure 6 illustrates a circuit diagram of the proximity switch device in one embodiment ; and Figure 7 is a schematic diagram of an embodiment of the present invention.

Referring firstly to Figure 1 there is illustrated a roller 2 for a conveyor belt system and a proximity switch device 4 in accordance with the invention positioned with respect to the roller 2. In operation, it is necessary to receive an indication if the roller noves excessively to the left or right, i. e. out of line, and conventionally it would be required to mount a proximity switch at the position 6 and a proximity switch at position 8, to measure movement of the roller in the direction of arrows 10, 12 respectively. However, using the proximity switch device in accordance with the current invention, only one device is required to be mounted at either of the locations 6 or 8 and in the Figure is shown at location 8, and still obtain an indication of movement in the direction of arrows 10, 12 between and beyond first and second switch locations indicated by numerals 9 and 11 for illustrative purposes, so that if the roller moves outwith the space 7 between the locations 9 and 11, then the switch changes condition and indicates that the roller is in an incorrect position.

To achieve this indication the proximity switch device 4 inclues a single sensor arrangement 14 for measuring movement of an item in the directions indicated by arrows 16 and 19 as shown in Figures 2 and 3 and in the direction 18 as indicated in Figures 4 and 5. In the Figures 3 and 5 the switch components are shown housed in a plastic tubing 16 for protection as required. In the switch shown in Figures 2 and 3 a cylindrical ferrite coil 13 is used to generate a wide ranging magnetic field which allows the ability to sense positions around the sensor. In Figures 4 and 5 a cup shaped ferrite core 15 is used to generate a unidirectional magnetic field which allows sensing of position at the end 17 of the sensor.

In each case the signals received from the sensor are processed and utilise in two ways as follows and with reference to Figure 6 also.

The proximity switching device of the invention has two locations at which the moveable item can be sensed and at which a change in condition of the device can occur and these are set as follows. When the moving item is in the desired position which is typically within the required range the sensing locations or switching points of the device are controlled so that the output signal is on or off as required. This means that the safety of the system is enhanced as the signal will fail to safe in the event of the proximity switch device being moved or detached from the fixed object or in the event of loss of electrical supply, damage to the wiring or damage to the switch unit.

In the Figure 6 the first circuit for the first location or switching point inclues an integrated circuit IC1 with a sensing coil L and other components to form an arrangement of an inductive switch which has a switching location, the position of which can be adjusted and set by the user, in this case via a screw head 21 which acts on VR1. The electrical output of IC1 appears at pin 5 and, via diode D1, turns on the output transistor TR1 at the switching location which has been set.

A second circuit for the detection of the second switching location inclues an integrated circuit IC2 which monitors the voltage produced from IC1 and generates an electrical signal at the second switching location, which location can be adjusted via screw head 23 which acts on VR2. The electrical signal output is used to turn off the output transistor TR1 so that the transistor is in effect only turned on when the moving item lies between the first and second switching locations with these locations being set by the user by using VR1 and VR2 for the first and second locations respectively.

It should however be appreciated that the circuit shown in Figure G only illustrates one of a range of possible embodiments.

The adjustment of the two switch locations is factory set via screw heads acting on VR1 and VR2, as shown in Figure 6. VR1 is used to adjust the point of resonance of the tuned circuit comprising L and C1 and by virtue of this resonance condition, the adjustment of VR1 is non-liner and this may result in incorrect adjustment by an unskilled person.

Referring to Figure 7, there is illustrated a schematic view where a microprocessor 25 is provided to create the adjustment of VR1, thus enabling a more linear signal to be generated than can be generated manually.

The microprocessor 25 generates a varying signal and records the value of that signal when the electrical output of IC1 reaches a maximum. In this way, the tuned circuit can be brought to an optimum resonance despite varying conditions, such as temperature and the influence of the surrounding metal. The value of the signal stored in the memory of the microprocessor 25 is further processed to produce an input signal which approximates to a more linear position of the item being sensed.

A display device 27 can be provided on which the approximate linear position can be displayed. The form of display can include a bar graph display created by LED, LCD technology and/or the like.

As such, the position of the item being sensed can be displayed within the band defined by the maximum and minimum location positions of the proximity switch.

Referring to Figure 7, two further adjustment potentiometers VR3 and VR4 can be provided, to signal to the microprocessor 25, the first location point and the second location point respectively. The microprocessor 25 in turn can produce one or more output signals which are dependent on whether the input signal, as mentioned above, is greater in value or less than the signal values generated by VR3 and VR4.

The values of VR3 and VR4 can also be displayed on display screen 27. The user can then adjust the sensing locations for the proximity switch whilst monitoring the position of the item being sensed relative to the sensing locations.

In the embodiments shown in Figures 2-5 the indication of the position of the moving item with respect to the proximity switch device is illustrated visually by means of lamps Y, R and G. In one use, the lamp Y is lit when the moving item is too far away from the proximity switch and therefore lies outside the space between the first and second switching locations and the lamp R is lit when the moving item is too close to the proximity switch and therefore lies outside the space between the first and second switching locations.

The lamp G is only lit when the moving object is within the space between the first and second switching locations, i. e. in the correct position.

Thus the present invention provides for the use of a proximity switch device which inclues one sensor arrange to provide an indication of the position of an item with respect to two locations which can be pre-set with the device. This over comes the need for a separate proximity switch to be used for each switching location and therefore reduces cost and the need for more than one mounting location and increases the electrical fail to safe aspects of the application.

Claims

CLAIMS :

1. A proximity switch device fitted to a first item for detecting movement of a second item with respect to the proximity switch device and wherein said proximity switch device comprises a sensor and is capable of sensing the position of said first item at at least two spaced locations, with respect to the proximity switch device.

2. A proximity switch device according to claim 1 wherein the first item is fixed and the proximity switch device provides an indication of the position of the second item with respect to the first item.

3. A proximity switch device according to claim 1 wherein a magnetic coil is provided which is capable of generating a magnetic field to sense positions around the sensor.

4. A proximity switch device according to claim 1 wherein a magnetic core is provided which is capable of generating a unidirectional magnetic field to sense positions at the sensor.

5. A proximity switch device according to claim 1 wherein the switch device can be controlled to change condition when the second item passes one of the at least two spaced locations.

6. A proximity switch device according to claim 1 wherein a first electronic circuit is provided to sense and cause a change in condition as the second item moves past a first location, and at least a second electronic circuit is provided to sense and cause a change in condition as the second item moves past at least a second location.

7. A proximity switch device according to claim 6 wherein a screw head is used to adjust the position of the first switching location and/or the at least second switching location.

8. A proximity switch device according to claim 6 wherein a microprocessor is provided to adjust the position of the first switching location and/or the at least second switching location.

9. A proximity switch device according to claim 1 wherein visual and/or audio indication means are provided to indicate the condition of the proximity switch device.

10. A proximity switch device according to claim 1 wherein visual and/or audio indication means are provided to indicate the first switching location, the at least second switching location and/or the position of the second item.

11. A proximity switch device according to claim 9 or 10 wherein the visual indication means inclues one or more LED's.

12. A proximity switch device according to claim 10 wherein display means are provided on which graphs and/or the like can be displayed.

13. A proximity switch device fitted to a first item for detecting movement of a second item with respect to the proximity switch device and wherein said proximity switch device comprises a first electronic circuit to sense and cause a change in condition as the second item moves past a first location, and at least a second electronic circuit is provided to sense and cause a change in condition as the second item moves past at least a second location.

14. A proximity switch device as herein described with reference to the accompanying Figures.