GB2515127A

GB2515127A - Safety switch and actuator

Info

Publication number: GB2515127A
Application number: GB1313374.9A
Authority: GB
Inventors: Mabruk Farrah; Matthew Bagley
Original assignee: MECHAN CONTROLS PLC
Current assignee: MECHAN CONTROLS PLC
Priority date: 2013-07-26
Filing date: 2013-07-26
Publication date: 2014-12-17
Anticipated expiration: 2033-07-26
Also published as: GB201313374D0; GB2515127B

Abstract

A magnetically operable safety switch arrangement includes a safety switch 1 and an actuator 2. The safety switch 1 includes an array of at least four magnet sensors (H1-4, fig 4). At least two sensors are arranged to be triggered by a magnetic field with a first orientation, and those two sensors are separated by at least one sensor arranged to be triggered by a magnetic field with a second, opposite, orientation, the switch being arranged to change state when all four sensors have been triggered. The actuator includes an array at least four magnets 3 arranged to trigger all the sensors (H1-4, fig 4) of the switch when the actuator is brought within a predetermined distance of, and alignment with, the safety switch. The safety switch may include relays, preferably at least two normally open relays connected in series and/or at least two normally closed relays connected in parallel.

Description

SAFETY SWYFCH AND ACTUATOR

Technical Field of the Invention

The present invention relates to a safety switch and actuator for the safety switch.

Background to the Invention

Safety switches are used, amongst other things, to prevent operation of machinery unless it is in a particular state, for example that a guard is in an operative position.

Non-contact safety switches comprise a switch and an actuator. When the actuator is brought into certain proximity of the switch the switch is triggered and changes state, typically to either complete or open an electrical circuit.

In a common type of tion-contact safety switch the actuator comprises a magnet and the switch a magnetic sensor. A problcrn with this arrangement is that the switch can potentially be triggered by a magnetic field other than that created by the actuator, either inadvertently or deliberately, with a consequent negative impact on safety.

Embodiments of the present invention have been made in consideration of this problem.

Summary of the Invention

According to an aspect of the present invention there is provided a magnetically operable safety switch comprising an array of at least Ibur magnet sensors wherein at least two sensors are arranged to be triggered by a magnetic field with a first orientation, and those two sensors are separated by at least one sensor arranged to he triggered by a magnetic field with a second, opposite, orientation, the switch being arranged to change state if all four sensors are triggered.

Such an arrangement of sensors camiot be triggered by a single magnet, and thus this significantly reduces the risk of the switch changing state other than under the influence olmagnetic held generated by a. dedicated actuator. The arrangementprovides for eight different relative orientations of sensors, and the addition of one or more additional sensors, or groups of four sensors, provides for many more. So it is possible to produce so called coded switches and actuators so that, on a given installation with several switches and actuators, one actuator is only capable of actuating one, or selected, switches.

The sensor away may be linear. The sensors may all be disposed in the same plane. The magnetic sensors may comprise Hall Effect devices. Hall Effect sensors have an advantage in that triggering the sensor does not depend upon thc direction in which it is approached by a magnet, in contrast, for example, to a reed switch. The sensors may be evenly spaced apart. The switch may comprise five or more sensors. [he switch may comprise eight sensors.

Two sensors may be arranged to be triggered by a magnetic field with a first orientation and two sensors arranged to he triggered by a magnetic field with a second, opposite, orientation. Alternatively three sensors may be arranged to be triggered by a magnetic field with a first orientation and one sensor arranged to be triggered by a magnetic field with a second, opposite, orientation.

The switch may comprise one or more relays which change state when the switch changes state. There may be at least one normally open relay and one normally closed relay. At least two normally open relays may he connected in series and/or at least two normally closed relays may be connected in parallel.

The switch may comprise at least two groups of four magnetic sensors arranged so that when all four sensors of one group are triggered one relay changes state and when all four sensors of the other group are triggered another relay changQs state.

According to another aspect of the present invention there is provided an actuator for a magnetically operable safety switch according to the first aspect of the invention, comprising an array olibur magnets, wherein at least two of the magnets have polarity of substantially the same orientation, and those two magnets are separated by at least one magnet with a polarity of substantially opposite orientation.

The array may be linear. The magnets may be permanent magnets. The magnets may be substantially evenly spaced.

The magnets may by substantially cylindrical. The magnets may be spaced apart by at least their width, diameter in the case of a cylindrical magnet. or at least twice or two and a half times their width. In some embodiments the magnets are spaced apart by at at least 6 or at least 12mm. This helps to ensure that the magnetic field produced by one magnet is sufficiently separated from that produced by adjacent magnet so that each magnet can only trigger a respective sensor of a similarly spaced sen sor array comprised in a switch.

Each magnet may have a smcngtli on the range 4 mT to 40 mT.

The magnets may be disposed in a housing. The magnets may be mounted adjacent to a first wall of the housing, and spaced from a second wall of the housing, opposite to the first wall. the magnets may be positioned, and the housing dimensioned so that if the first wall of the housing is brought into contact with a switch intended for use with the actuator the magnets will actuate the switch, hut if the second wall of the housing is brought into contact with the switch the magnets will not actuate the switch.

The magnets may be spaced from the second wall ofthe housing by more than 10, 15 or 20mm.

The invention also provides a safety switch arrangement comprising a magnetically operable safety switch according to the first aspect of the invention and at least one actuator according to the second aspect of the invention whercin the maguets of the or each actuator are arranged to trigger all of the sensors of the safety switch together when the actuators are brought within a predetermined distance of, and alignment with, the safety switch.

The spacing of the sensors may substantially correspond to the spacing of the magnets.

Detailed Description of the Invention

in order that the invenlion may be more clearly understood, embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, iS of which: Figure 1 shows a first embodiment of a safety switch and actuator; Figure 2 shows a plan view of the actuator with top removed; Figure 3 shows a perspcctivc view of the actuator of figure 2; Figure 4 shows a printed circuit board supporting an array of sensors of the safety switch of figure 1; Figure 5 shows a schematic circuit diagram of the safety switch of figure 1; Figure 6 shows a second embodiment of a safety switch and actuators; and Figure 7 shows a schematic circuit diagram of the safety switch of figure 6.

Referring to figures 1 to 5 a safety switch arrangement comprises an electrical switch 1 and an actuator 2. When Lhe switch 1 and actuator 2 are brought together in a predetermined alignment to within a predetermined distance of each other the actuator causes the switch ito change state. The arrangement would typically be used to prevent operation of a machine unless components of the machine to which the switch 1 and actuator 2 are mounted respectively are positioned such that the state of the switch 1 is changed by the presence of the actuator 2. An example would be to prevent operation of a machine unless a safety guard was in an operative position.

The switch I and actuator 2 each comprise sealed, substantially cuboidal housings.

The actuator 2 housing comprises a hollow housing which houses a linear array of four substantially cylindrical permanent magnets 3 substantially evenly spaced along a long side wall of the actuator housing ith a respective maet at each end of that wall.

The magnets is formed from Neodymium (N3 8-45). Each magnet is arranged so that its North and South poles arc aligned along the rotational axIs of the cyllndcr, thc axis extending substantially perpendicularly to the side wall of the actuator housing. In this embodiment the diameter of the magnets is about 6mm and the length of the sidewall of Ihe housing along which they are arranged, internal to the housing, is about 50mm. Other dimensions are of course possible.

Th.e housing is formed from a plastics material, Tn other embodiments it is formed from stainless stecl. t'he housing is filled with a resin material (not shown) which encapsulates the magnets.

In the illustrated actuator 2, the magnets are arranged with alternating polarity, as labeled in figure 2. Other arrangements are possible, provided that two of the four magnets with polarity of the same orientation are separated by at least one magnet with polarity of the opposite orientation.

Two generally circular apertures 4 extend through the housing of the actuator 2 to enable the aciLlator to he fastened to a machine, or other item, by way of screws or other fasteners. tubes 5 extend between the apertures in opposite faces of the housing, so that the apertures do not communicate with the remainder of the inside of the housing.

The switch 1 housing is also hollow and is of substantially the same size and dimensions as the actuator housing. An elongate printed circuit board 6 is mounted along and adjacent to the inside of a long side wall of the housing. An eight core electrical cable 7 is connected to terminals on the printed circuit board 6 and extends out of the housing through an aperture formed in the opposite long side wall to that behind which the circuit board 6 is mounted. Four Hall Effect devices Hi -4 arc mounted on the printed circuit board 6. The devices all lie substantially in the same plane and are spaced substantially evenly along the length of the circuit board 6. The devices are arranged on the circuit board, and the circuit board is arrangcd in the housing, so that thc plane in which the devices lie is substantially parallel to the inside of the side wall of the housing adjacent which they are positioned, and so that the devices HI, P4 at each end of the circuit board 6 are adjacent the inside of the shorter walls of the housing. That is to say, the Hall Effect devices are arranged in thc switch housing in the same way that the magnets 3 are arranged in the actuator housing. Adjacent Hall Effect devices face in opposite directions, so they arc sensitive to oppositely directed magnetic fields. The relative orientation of the Hall Effect devices thus corresponds to the orientation of the niaguets. Indeed, if a different orientation of magnets is used, a corresponding different orientation of Hall Effect devices should be adopted.

The printed circuit board 6 supports an electrical circuit as shown schematically in figure 5. The circuit comprises input terminals Al and A2 which, in use, are connected to +24Vdc and ground of a suitable power supply.

The circuit comprises various components to protect Lhe circuit mid regulate its power supply. Diode Dl protects the circuit in the event that the power supply is connected incorrectly. Capacitor Cl is a smoothing capacitor, provided, to smooth any ripples in the supply voltage. Resistor Ri limits the current drawn by Zener diodes D2 and D4 which, in turn, limit the maximum voltage across the circuit to 24Vde. Light emitting diode (LED) LED 1 is a bi-colour LED. When power is supplied to the circuit it illuminates red, drawing current via D2, which flows through the diode via resistor R4 and transistor Q2.

The four Flail Effect devices, 1-11-4, are connected across the regulated power supply and in series with each other. A respective bypass capacitor C2-5 is connected between the V0 and GND tcrminnls of each hail Effect device to reduce external noise and noise generated by the Hall Effect device.

When each Hall Effect device is activated by a magnetic flcld with the correct orientation the resulting current flow causes the current to reverse through the Bi<olour LED 1, which then illuminates green. In addition, activation of all of the Hall effect devices causes current to flow through Mofset relays lJl-3 causing their contacts to change state. Relays U 1 and 2 have normally open contacts, and relay U3 has normally closed contacts.

In use, the circuit is connected to an appropriate power supply and. the outputs of the Mofset relays UI -3 are connected to appropriate control circuitry of a machine or other device to be control led by the switch, and the switch 1 and actuator housings 2 are mounted appropriately to the machine or other device.

When the actuator 2 approaches the switch 1 with the correct orientation, the four magnets 3 in thc actuator become positioned adjacent respective Hall Effect devices 1-11-4 in the switch. As the orientation of the magnets matches Lhat of the Hall Effect devices, each device is activated, causing the bi-colour LED to change colour and the Mofset relays UI -3 lo change state.

Provision of four Hall Effect devices in a linear array, with at least two devices of the same orientation being separated by at least one device with an opposite orientation, provides considerable security against accidental or deliberate operation by a magnet other than those of a matched actuator, or by a matched actuator in an inverted or rotated state. TI a matched actuator is inverted or rotated, the orientation of magnets in the actuator will no longer match the orientation of Flail Effect Devices iii the switch. Even if, the actuator is rotated and inverted, so that the magnets 3 are correctly oriented relative to the lid.! Effect dcvi ces 1-11 -4, the switch will still not he triggered because the magnets will be at the side of the actuator remote from switch when the actuator approaches the switch and the magnetic field is then insufficiently strong to trigger the Hall Effect devices. In contrast to arrangements with three Hall Effect devices, it is not possible to trigger the switch with a single magnet.

Integrity of the switch can be further improved by increasing the number of Hall Effect devices to a number greater than four. With five or more Hall Effect devices there is a far greater number of ways of orienting the devices enabling a number of uniquely coded actuator switch pairs to be produced.

In an alternative embodiment eight Hall Effect devices are provided. This is illustrated in figures 6 and 7. This embodiment comprises single switch unit 1, which is used in conjunction with two actuators 2. The actuators 2 are identical to that illustrated in figures 1 to 3, save that orientation of the four magnets maybe altered as desired.

The switch comprises an elongate housing which houses a printed circuit board, similar to the type shown in figure 4, but supporting two, spaced apart, arrays of four Hall Effect Devices arranged for activation by the two actuators, one actuator for each 1 0 activating each array.

The switch is arranged so that both arrays of four Hall Effect devices must be triggered in the appropriate way in order to change the state of the switch.

Figure 7 is a schematic view of the electrical circuit comprised in the switch, which is to a large extent a combination of two circuits of the type shown in figure 5.

A similar arrangement is provided to regulate and protect the circuit from the power supply.

Each array of four Hall Effect devices is connected in series and arranged to drive two normally open UI, U2, U4, US and one normally closed U3, U6 Mofset relay. Each normally open relay associated with one array is connected in series with a normally open relay associated with the other array between a pair of terminals, in this case terminals 13 and 14, and 23 and 24. The normally closed relays associated with each array of 1-Tall Effect devices are connected in parallel between terminals 31 and 32. So, the circuit provides the same switching functionality as that shown in figure 5 except that switching only talces place if all eight Hall Effect devices are correctly triggered. It also provides for the same eight connections that are provided on the circuit shown in figure 5, and so can he wired in exactly the same way.

The circuit offigure 7 has a different arrangement of light emitting diodes (LEDs) to indicate its operation to the circuit of figure 5. LED1 illuminates when power is provided to the circuit. LEDs 2 and 3 illuminate when the hail Effect devices withwhich they are associated (LED2 is associated with Hall effect devices 111-4 and LED3 is associated with Hall Effect devices H4-8) are triggered, and therefore indicate that the Mofset relays they control have changed state. LED4 illuminates when all eight hall Effect devices have been triggered.

As the switch of this embodiment can be used with two actuators it can replace two switches of the type shown in figure 1 where they need to be deployed side by side, for example to ensure that double doors are closed before a machine is permitted to operate. In these circumstances the doubled headed switch shown in figure 6 confers advantages over the use of two separate single headed switches. It is only necessary to install one switch, the double headed switch is more economic to produce than two single headed switches and wiring in simplified in that only one set of eight connections nccd be made to the switch, compared to two sets, i.e. sixteen connections, for a pair of single headed switches T'he above embodiments arc described by way of example only. Many variations are possible without departing from the scope of the invention as defined in the appended ci ai ins.

Claims

CLAIMS1. A magnetically operable safety switch comprising an array of at least four magnetic sensors wherein at least two sensors arc arranged [0 be triggered by a magnetic field with a first orientation, and those two sensors are separated by at least one sensor arranged to be triggered by a magnetic field with a second, opposite, orientation, the switch being arranged to change state if all four sensors are triggered.
2. A magnetically operable safety switch as claimed in claim 1 wherein the array is linear.
3. A magnelically operable safety switch as claimed in claim I or 2 wherein the magnetic sensors are all disposed in the same plane.
4. A magnetically operable safety switch as claimed in any preceding claim wherein the magnetic sensors comprise Hall Efibet devices.
5. A magnetically operable saièty switch as claimed in any preceding claim wherein the magnetic sensors are evenly spaced apart.
6. A magnetically operable safety switch as claimed in any preceding claim having five or more sensors.
7. A magnetically operable safety switch as claimed in any preceding claim having eight sensors.
8. A magnetically operable safety switch as claimed in any preceding claim wherein two sensoifs are arranged to be triggered by a magnetic field with a first orientation and two sensors arc arranged to be triggered by a magnetic field with a second, opposite, orientation.
9. A magnetically operable safety switch as claimed in any of claims 1 to 7 three sensors are arranged to be triggered by a magnetic field with a first orientation and one sensor is arranged to be triggered by a magnetic field with a second, opposite, orientaLloil,
10. A magnetically operable safety switch as claimed in any preceding claim wherein, comprising one or more relays which change state when the switch changes state.
11. A magnetically operable safety switch as claimed in claim 10 comprising at least one normally open relay and one normally closed relay.
12. A magnetically operable safety switch as claimed in claim 11 wherein at least two normally open relays are connected in series and/or at least two normally closed relays are connected in parallel.
13. A magnetically operable safety switch as claimed in claim Ii or 12 comprising at least two groups of four magnetic sensors and arranged so that when all four sensors of one group are triggered one relay changes state and when all four sensors of the other group are triggered another relay changes state.
14. An actualcr For a magnetically opcrable safety switch as claimed in any preceding claim comprising an array of four magnets, wherein at least two of the magnets have polarity of substantially the same orientation, and those two magnets are separated by at least one magnet with polarity of substantially opposite orientation.
15. An actuator as claimed iii claim 14 wherein the array is linear.
16. An actuator as claimed in either claim 14 orl5 wherein the magnets arc permanent nmgn.ets.
17. An actuator as claimed in any of claims 14 to 16 wherein the magnets are substantially evenly spaced.
18. An actuator as claimed in and of claim 14 to 17 wherein the magnets are spaced apart by at least their width.
19. An actuator as claimed in any of claims 14 to 18 wherein the magnets are disposed adjacent to a first wall ofthe housing, and spaced from a second wall of the housing, opposite to the first wall.
20. An actuator as claimed in claim 19 wherein the magnets are spaced from the second wall of the housing by at least 10mm.
21. A safety switch arrangement comprising a magnetically operable safety switch as claimed in any of claims 1 to 13 and at least one actuator as claimed in any of claims 14 to 17 wherein the magnets of the or each actuator are arranged to trigger all of the sensors of the safety switch together when the actuators are brought within a predetermined distance of, and alignmcnt with, the safety switch.
22. A safety switch arrangement as claimed in claim 18 wherein the spacing of the sensors substantially corresponds to he spacing of the magnets.
23. A magnetically operable safety swiich substantially as herein described with reference to the accompanying drawings.
24. An actuator for a magnetically operable safety switch substantially a herein described with reference to the accompanying drawings.Amendments to the claims have been filed as foflowsCLAIMS1. A safety switch arrangement comprising a magnetically operable safety switch and two separate actuators, the magnetically operable safety switch comprising a housing containing two, spaced apart arrays of at least four magnetic sensors wherein at least two sensors of each array are arranged to be triggered by a magnetic field with a first orientation, and those two sensors are separated by at least one sensor arranged to be triggered by a magnetic fi&d with a second, opposite, orientation, each of the two actuators comprising an array of four magnets, wherein at least two of the magnets have polarity of substantially the same orientation and those magnets are separated by at least one magnet with polarity of substantially opposite orientation, wherein the magnets of each actuator are arranged to trigger all of the sensors of a respective array of sensors of the safety switch together when the actuator is brought within a predetermined distance of, and aligned with, the safety switch and the safety switch is arranged so that both arrays of magnetic sensors must be triggered in the appropriate way in order to change the state of the switch.2. A safety switch arrangement as claimed in claim I wherein either or each array is linear.3, A safety switch arrangement as claimed in claim I or 2 wherein the magnetic sensors in each array are all disposed in the same plane.4. A safety switch arrangement as claimed in any preceding claim wherein the magnetic sensors comprise Hall Effect devices.5. A safety switch arrangement as claimed in any preceding claim wherein the magnetic sensors in each array are evenly spaced apart.6. A safety switch arrangement as claimed in any preceding claim having five or more sensors in each array.7, A safety switch arrangement as claimed in any preceding claim having eight sensors in each array.8. A safety switch arrangement as claimed in any of claims I to 5 wherein two sensors in either or each array of sensors are arranged to be triggered by a magnetic field with a first orientation and two sensors in either or each array are arranged to be triggered by a magnetic field with a second, opposite, orientation, 9. A safety switch arrangement as claimed in any of claims Ito S wherein three sensors in either or each array are arranged to be triggered by a magnetic field with a first orientation and one sensor is arranged to be triggered by a maetic field with a 0 second, opposite, orientation, C) 10. A safety switch arrangement as claimed in any preceding claim, comprising one or more relays which change state when the switch changes state.11. A safety switch arrangement as claimed in claim 10 comprising at least one normally open relay and one normally closed relay.12, A safety switch arrangement as claimed in claim II wherein at least two normally open relays are connected in series and/or at least two normally closed relays are connected in parallel.13. A safety switch arrangement as claimed in claim 11 or 12 wherein when all four sensors of one array are triggered one relay changes state and when all four sensors of the other array are triggered another relay changes state.14. A safety switch arrangement as claimed in any preceding claim wherein the array of magnets in either or each actuator is linear.15, A safety switch arrangement as claimed in any preceding claim wherein the magnets are permanent magnets.6. A safety switch assembly as claimed in any preceding claim wherein the magnets in either or each actuator are substantially evenly spaced.7. A safety switch assembly as claimed in any preceding claim wherein the magnets of either or each actuator are spaced apart by at least their width.8. A safety switch assembly as claimed in any preceding claim wherein each actuator comprises a housing and the magnets of each actuator are disposed adj acent to a first wall of the housing, and spaced from a second wall of the housing, opposite to the first wall. a)CJ 19. An actuator as claimed in claim 18 wherein the magnets are spaced from the second wall of the housing by at least 10mm.20. A safety switch arrangement as claimed in any preceding claim wherein the spacing ofthe sensors in each array substantially corresponds to the spacing ofthe magnets in each actuator.21. A safety switch arrangement as claimed in any preceding claim wherein each array of magnetic sensors is connected in series and arranged to drive two normally open and one normally closed relay, each normally open relay associated with one sensor array is connected in series with a normally open relay associated with the other array between a pair of terminals and the normally closed relays associated with each sensor aray are connected in parallel between a pair of terminals.22. A magnetically operable safety switch substantially as herein described with reference to the accompanying drawings.23. An actuator for a magnetically operable safety switch substantially as herein described with reference to the accompanying drawings. a) (4