Patent Application
20090194405
This application claims priority to Great Britain Patent Application No. 0801704.8 filed on Jan. 31, 2008, and the disclosure of which is expressly incorporated herein.
The present invention relates to a safety switch, and in particular a safety switch arrangement.
Safety switches are well known, and are typically used to prevent access to for example dangerous electromechanical machinery when that machinery is in operation. In a conventional arrangement the safety switch is mounted on a doorpost of a machinery guard, and an actuator for the safety switch is mounted on a corresponding door. When the door is closed the actuator engages with the safety switch, which in turn closes a set of electrical contacts which allow power to be supplied to the machinery. This arrangement ensures that power can only be supplied to the machinery when the guard door is shut. When the guard door is opened, the actuator disengages from the safety switch, thereby opening the electrical contacts and cutting off the supply of power to the machinery.
A typical safety switch comprises a housing, in which is provided a set of contacts fixed in position relative to the housing. An axially slideable plunger is mounted inside the housing, and is moveable relative to the housing. The plunger (or another plunger in contact with the plunger, for example a contact block plunger) is provided with another set of contacts. The plunger is biased towards a cam arrangement by a spring. The actuator mentioned above is arranged to engage with the cam arrangement.
In many safety switches, if the actuator is not engaged with the cam arrangement (i.e. if the actuator is not engaged with the safety switch), the cam arrangement is arranged to prevent the contacts on the plunger coming into contact with the contacts of the housing by preventing movement of the plunger (i.e. the plunger is kept in a first plunger position). By preventing the contacts from contacting one another, the switch cannot conduct electricity while the actuator is not engaged with the cam arrangement.
Bringing the actuator into engagement with the cam arrangement causes the cam arrangement to rotate, which in turn causes the plunger (which is biased toward the cam arrangement) to move into a notch provided in the cam arrangement. The plunger is then in a second plunger position. When the plunger moves into the notch, the contacts on the plunger are brought into contact with the contacts of the housing, allowing electricity to flow through the safety switch.
Before a safety switch is sold to a customer, it is often desirable to undertake certain tests on that safety switch, or on a safety switch similar to that safety switch (for example, a safety switch from the same batch, production run, series of safety switch, etc.) to validate the quality of construction and operability of the switch. For instance, it may be desirable for the manufacturer or supplier of the safety switch to ensure that the safety switch performs to a desired level, for example a level quoted in literature or marketing documentation. The tests may also be desirable to ensure that the safety switch is of a desired standard, and is, for example durable enough to be used in the conditions in which the safety switch is intended to be used. For instance, in some jurisdictions throughout the world, safety switches have to meet certain safety criteria (for example, safety standards set by governments or government related bodies) which these switches have to meet in order to be sold or used in that particular country.
The testing mentioned above may take one of a number of forms. For instance, an actuator may be repeatedly engaged with and disengaged from the safety switch to check that the safety switch remains operable during and after the repeated engagement and disengagement. For example, the actuator may be engaged with and disengaged from the safety switch a hundred thousand times to ensure that, when sold, thereby increasing confidence that the same or similar safety switch will not fail prematurely.
If the safety switch (or switches) in question pass the test, the safety switch can be sold with reasonable confidence that the switch is durable enough to withstand a desired or expected number of operations. However, once sold, there is no way of telling how many times the safety switch has been used. For instance, there is no way of telling how many times somebody has entered and left an enclosure incorporating such a safety switch, and therefore how many times an actuator has been engaged with and disengaged from the safety switch. More importantly, there is no way of telling whether the safety switch is being used or has been used to such an extent that it exceeds the level up to which it was initially tested. For example, if the safety switch was tested to ensure that it retained structural integrity and an operating state for 50,000 operations, once installed for use, there is no reasonable way of telling the number of uses of the switch by the end user. That is, for an exemplary switch having an asserted useable life of at least 50,000 uses, there is no reasonable means for assessing if the end-user of the safety switch has used it 25,000 times and is within the level of testing, or if the end-user has used it 100,000 times and exceeded the level of testing. Since the safety switch may not have been tested to the extent which the end-user has used the switch, there is no way of telling if the safety switch is as safe as was intended. Clearly this is undesirable.
It is therefore an object of the present invention to provide a safety switch arrangement which may overcome or substantially mitigate at least one disadvantage of the prior art, whether identified herein or elsewhere.
According to the present invention there is provided a safety switch for affecting the operating state of equipment to which the safety switch is at least indirectly connected. The safety switch includes a configuration arranged to change from a first condition to a second condition depending on whether or not an actuator has been engaged with or disengaged from the safety switch. The safety switch includes an arrangement for determining information that is at least indicative of an operational property of the configuration, and for storing information that is at least indicative of the obtained information.
Preferably, the information may be stored with a display device. Alternatively, the information may be stored in a memory.
The configuration may be electromechanical. The configuration may comprise a contact that is fixed in position relative to the safety switch and a contact that is moveable relative to the safety switch. The moveable contact is preferably moveable into and out of contact with the fixed contact such that electrical current can or cannot flow between the moveable and fixed contacts. The configuration may comprise a fixed pair of contacts that are displaced from one another and a moveable bridging contact. The moveable bridging contact is preferably moveable into and out of contact with the fixed pair of contacts such that electrical current can or cannot flow through the bridging contact. The moveable contact may be carried by a plunger.
The arrangement may be configured to detect an electrical signal, or change in an electrical signal associated with the configuration. The arrangement may be configured to detect an electrical signal, or change in an electrical signal associated with the configuration when the configuration changes from the first to the second condition. The arrangement may be configured to detect a change in one or more of a current flowing through the arrangement, a potential difference across the arrangement, or a resistance of the arrangement. The arrangement may be configured to store information that is at least indicative of the number of times the change is detected. The arrangement may be configured to store the value of the current, potential difference, or resistance. The arrangement maybe configured to store the value of the current, potential difference or resistance each time the current, potential difference or resistance is detected to be above or below a pre-determined threshold. The arrangement may be configured to store the number of times the value of the current, potential difference or resistance each time the current, potential difference or resistance is detected to be above or below a pre-determined threshold. The arrangement may comprise an electrical circuit.
The arrangement may be arranged to detect mechanical movement of a part of the configuration. The arrangement may be arranged to detect movement of one or more of a cam arrangement, a plunger or a moveable electrical contact of the configuration of the safety switch, or the actuator when it is brought into or out of engagement with the configuration. The arrangement may be configured to store the number of times movement is detected. The arrangement may be configured to store the number of times movement is detected beyond a threshold value. The threshold value may correspond to the amount of movement necessary for the configuration to change from a first condition to a second condition.
The safety switch may be provided with a counter, with which information at least indicative of an operational property of the configuration may be stored. The counter may be electrical in nature. The counter may be mechanical in nature.
The safety switch may be provided with a display arranged to provide a visual indication of information at least indicative of an operational property of the configuration of the safety switch. The display maybe the counter mentioned above.
In use, the safety switch maybe arranged to be connected to the equipment using a wired arrangement. In use, the safety switch may be arranged to be connected to the equipment using a wireless arrangement.
The first condition of the configuration may be such that the supply of electricity to the equipment is allowed, and the second condition is such that the supply of electricity to the equipment is prevented. The first condition of the configuration may be such that the equipment is arranged to operate at a first speed, and the second condition is such that the equipment is arranged to operate at a second speed. The first condition of the configuration may be such that movement of at least a part of the equipment is allowed, and the second condition is such that movement of the equipment is prevented.
Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
a and 2b schematically depict a cam arrangement of the safety switch of
a and 4b schematically depict circuit arrangements in accordance with an embodiment of the present invention;
a to 6d schematically depict operating principles of a display of the safety switch of
The plunger 4 is biased by a spring 5 towards a second part of the housing, which forms a head 6 of the safety switch. The head 6 of the safety switch is provided with a rotatable cam arrangement 7. The cam arrangement 7 is arranged to receive and engage with an actuator (not shown in
a and 2b illustrate the interaction between the cam arrangement 7 and the plunger 4 in more detail.
It can be seen from
b depicts an actuator 10 that has been brought into engagement with the cam arrangement 7. It can be seen from
The thus far described features and operating mechanisms of the safety switch can be found in prior art safety switches. The safety switch shown in and described with reference to
a and 4b schematically depict circuits which give an example of how the circuitry 100 may obtain information that is indicative of the operation of the safety switch. The circuitry 100 is shown as being in electrical connection with two fixed safety contacts 2 of the safety switch (the rest of the safety switch is not shown for clarity). Movable safety contacts 2a are also shown in relation to the fixed safety contacts 2. In practice, and as illustrated in
b shows the situation when the movable safety contacts 2a have been brought into contact with the fixed safety contacts 2. For example, such movement may be undertaken when the actuator is brought into engagement with the safety switch, or is disengaged from the safety switch, as described above in relation to earlier Figures. It can be seen that the movable safety contacts 2a electrically connect the fixed safety contacts 2. In other words, the movable safety contacts 2a serve as bridging contacts, extending between the two fixed safety contacts 2. It can also be seen that an electrical circuit has now been formed. The circuitry 100 can use the opening or closing (or in other words, making or breaking) of the safety contacts 2, 2a to obtain information indicative of the operation of the safety switch.
In one example, each time the movable safety contacts 2a are moved into contact with and bridge the fixed safety contacts 2, electrical current may flow through the circuitry 100. Each time current flow is detected, a counter of circuitry 100 may be increased. The counter may be increased incrementally, or in any suitable manner, and may be stored in the circuitry 100, be part of the circuitry 100, or be in connection with the circuitry 100. The counter will therefore contain information at least indicative (and more likely directly proportional to or equal to) the number of times the safety contacts 2, 2a have been brought together. In other words, the counter will store information at least indicative of the number of times an actuator has been engaged with the safety switch. The circuitry 100 may be arranged to detect the absence or a reduction in the current, such that the opening, breaking, moving apart, etc., of the moveable safety contacts 2a and fixed safety contacts 2 may also be detected and used to affect the value of a counter. As mentioned above, information in or on the counter may be stored and/or displayed. A user of the safety switch may be able to access this information, virtually or otherwise, in order to determine if the safety switch has been used for a number of occasions which is approaching, equal to or exceeding a previously determined or defined testing threshold.
It is appreciated that there are a number of ways of assessing the number of operations of the safety switch. For example, circuitry 100 can count the number of times the safety contacts 2, 2a are brought into contact with one another, or the number of times when the safety contacts 2, 2a are moved apart from one another. When, for instance, the safety contacts 2, 2a have been brought into contact with one another, other information may be obtained. For example, the current flowing through the safety contacts 2, 2a may be determined, or the resistance across the contacts 2, 2a, or the potential different across the contacts 2, 2a. All such information may be used to obtain information at least indicative of the operation of the safety switch. For instance, an increase in the measured resistance may indicate a build up of debris or similar between the fixed contacts 2 and the movable contacts 2a. An increase in resistance up to or beyond a certain level may detract from operation of the safety switch and/or render the safety switch inoperable. The circuitry 100 can store information indicative of the current flowing through the contacts, the resistance across the contacts, or the voltage across the contacts, or may add to a counter each time the measured values are lower than or exceed a threshold value. Such information may be stored and/or displayed such that a user of the safety switch may be able to easily access information regarding the operation of the switch.
a to 6d schematically depict examples of how the display 120 can provide information at least indicative of the state of the counter mentioned above. In
b shows that the display 120 may be arranged to display a first colour, then a second colour, and then a third colour. The first colour may be indicative of a counter value which is below a first threshold value. The second colour may be indicative of a counter value which is between the first threshold value and a second threshold value, for instance when maintenance of the switch, or replacement of the switch is recommended. The display 120 could then change to the third colour when the counter value exceeds the second threshold value. This may be, as described above, when the counter exceeds a value for which the switch was tested.
c illustrates how the display 120 can display the value of the counter itself, such that the user may accurately determine operational information of the safety switch, for example, the number of times an actuator has been engaged with and disengaged from the safety switch.
d shows how the display 120 can display textual information which may for example provide instructions to the user. For instance, it can be seen in the Figure that the display 120 changes from displaying “OPERATIONAL” to “CONTACT ENGINEER”. The display 120 may be arranged to display the term “CONTACT ENGINEER” (or other text) when the counter exceeds a threshold value, for example.
It will be appreciated that the display 120 may be electronic, or mechanical, and may be configured to display any desirable information. The information which the display 120 is configured to display to the user may be dependent upon language requirements, safety requirements or any other requirements. For instance, it may be preferable to use block changes in colour as opposed to text.
In the foregoing description, circuitry 100 has been described. The circuitry 100 allowed information indicative of the operation of the safety switch to be obtained electrically. It is appreciated that similar and/or other information indicative of the operation of the safety switch may be obtained, at least in part, by mechanical means.
It is further envisioned that, rather than the mechanical detection of movement of the cam arrangement, movement of the contacts or plunger may be mechanically detected. For instance, the contacts or plunger may be arranged to contact a lever or other mechanism each time the contacts or plunger move. In one example, the plunger may be provided with a protrusion which impacts against the lever each time the actuator is engaged or disengaged with the switch. Movement of the lever may be used to increase a mechanical or electrical counter. The number of times that any part of the safety switch moves may be detected and stored to give, for example, an indication of the number of times the switch has been used. The number of times that movement of such a part is detected beyond a threshold value may be stored. For instance, the threshold value may correspond to the amount of movement necessary for the part to move a distance that it would need to move in order for the safety switch as a whole to move from a first condition to a second condition (e.g. to a non-conducting state from a conducting state, or to a conducting state from a non-conducting state).
Alternatively or in addition to displaying information indicative of the operation of the safety switch, other functionality may be provided. For instance, if the electrical or mechanical counter reaches or exceeds a threshold value, the safety switch could be moved to a condition whereby it cannot conduct electricity to electrical machinery that the switch is in connection with. For instance, upon reaching a threshold value the circuitry could be arranged to open or close a switch to ensure that the safety switch cannot conduct electricity to electrical machinery that the switch is in connection with. Upon reaching such a threshold value, opening or closing of a switch could be undertaken mechanically. For instance, in a mechanical incremental counter, when a dial representing the number in the tens of thousands moves from 0 to 1, the movement may trigger the opening or closing of a switch. In another example, the information indicative of the operation of the switch may be stored as well as or instead of initiating incremental switch movement. It is further envisioned that the stored information may be accessed by connecting another device to the safety switch, either using a wired or wireless link. For instance, the circuitry may communicate with a control device in a wired or wireless manner, and the control device could be arranged to control the operating state of machinery based on the information obtained by the circuitry.
In general, the present invention provides a safety switch for affecting the operating state of equipment to which the safety switch is at least indirectly connected. The safety switch includes a configuration that is arranged to change from a first condition to a second condition depending on whether or not an actuator has been engaged with or disengaged from the safety switch. The safety switch includes an arrangement for determining information that is at least indicative of an operational property of the configuration and for storing information that is at least indicative of the obtained information. The safety switch may be directly or indirectly connected to the equipment in a wired or wireless manner, respectively. The configuration could be a set of contacts, as described above, or it could be any electrical, mechanical or electromechanical configuration such as a solid state electronic arrangement or the like. The actuator may physically move at least a part of the configuration, for example the cam arrangement described above. Alternatively, the actuator could be a magnet or other apparatus that can change the state of the configuration without necessarily any physical contact. The arrangement for determining the information could be electrical, mechanical or electromechanical in nature, or a combination of these. The information may be stored in the form of an output, a display or in a memory. The display need not be electrically powered, but could instead be entirely mechanical in nature.
In the embodiments described above, a plurality of safety contacts has been described. However, it will be appreciated that any suitable configuration of safety contacts (and even auxiliary contacts) may be employed. For example, a plunger may be provided with only a single safety contact, and not two as shown in the Figures. In some embodiments a plunger provided with contacts extending through it may be located in a contact block or the like. The plunger in the contact block may be biased against a surface of the cam arrangement. Alternatively, the plunger in the contact block may be biased against an intermediate plunger located substantially outside of the contact block. The intermediate plunger may be biased against the cam arrangement by the contact block plunger.
It will be understood by the skilled person that a contact is a conductor which may be shaped at each of its ends, i.e. to define contact points. In the above described embodiments, the moveable safety and auxiliary contacts are conductors which extend transversely through the plunger, and protrude from both sides of the plunger (e.g. they are bridging contacts). The fixed contacts are conductors fixed in position relative to the housing of the safety switch.
The plunger of the present invention has been described in relation to a safety switch having a fixed set of contacts located and fixed in position in the housing of the safety switch. The fixed contacts of the housing may be individually fixed or integral to the housing, or may form part of a safety switch contact block. The safety switch contact block is a structure that is provided with the fixed contacts (or conductors). The safety switch contact block as whole is fixed in position into the housing. As such, it is appreciated that the fixed safety contacts (conductors) may be formed integrally with the housing, individually fixed in position in the housing, or form part of a contact block which is itself fixed in position in the housing.
In the foregoing description, the safety switch has been described as having a cam arrangement and plunger co-operable with the cam arrangement. It is appreciated that other mechanisms can provide similar operability. Any mechanism may be used to convert the engagement or disengagement of an actuator into, for example, opening and closing of one or more sets of contacts. For example, the engagement of the actuator with the safety switch may push against the contacts themselves. Alternatively, there may be an intermediate structure between the contacts and the actuator. For instance, the actuator may come into contact with and move a rod or elongate element which may push against the contacts or something carrying the contacts.
In the foregoing description, the making or breaking, or opening or closing, of contacts has been described as having the effect of allowing or preventing the safety switch from conducting electricity to electrically powered machinery. Generally, opening or closing of the contacts has the more general effect of changing the operating state of the machinery, for example slowing the machinery down, or stopping its movement while still maintaining its power supply. The changing of the operating state may be controlled directly by the safety switch (e.g. power supplied or not supplied) or by a control arrangement in communication with the safety switch and the machinery. The opening or closing of contacts in the safety switch may be used by the control arrangement to determine the control that is required to alter the operating state of the machinery. For example contacts open/closed may result in the control arrangement controlling the machine such that it slows down.
It will be appreciated by a person skilled in the art that the invention is not limited to the embodiments described above, and that various modifications may be made to those and other embodiments without departing from the invention, which is defined by the claims which follow.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0801704.8 | Jan 2008 | GB | national |
