Abstract:
A safety position switch including a push rod which responds to the movement of an actuator connected to a device to be made safe in order to act upon an electrical device by a lockable transmission mechanism acted on by the push rod. The transmission mechanism includes a pivoting lever capable of assuming a locked position and an unlocked position. The pivoting lever has force applied to it from the push rod such that a movement of translation of the push rod generates a rotation of the lever and the pivoting lever has an arm with a jamming element that is applicable, in the locked position of the lever and transversely with respect to the main axis, against the locking head.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a safety position switch of the type comprising a push rod which responds to the movement of an actuator connected to a device to be made safe, in such a way as to become displaced along a main axis in order to assume a rest position and a working position, comprising an electrical device, in particular a contacts block, switchable according to the position of the push rod, by means of a lockable transmission mechanism actuated by the push rod, and comprising a device for locking the transmission mechanism, which has a head for locking the mechanism, the locking head being capable of assuming a locked position and an unlocked position. 
   2. Description of the Related Art 
   In order to simplify the description, the expression “safety position switch” will hereafter be replaced by the expression “safety switch”. 
   Safety switches of the type described above are known for example from the document EP 817 227. These switches are associated with devices to be made safe, such as dangerous machines. 
   The locking device of the transmission mechanism is frequently produced in the form of an electromagnet disposed laterally with respect to the actuating head/push rod/contacts block assembly. It can also be a manually controlled device, for example by a key, or a pneumatic device or any other similar driving device. 
   Other safety switches have an elongated arrangement, or are of the “vertical” type, such that the locking electromagnet is located in the axis of the push rod and of the contacts block to be actuated (see for example EP 801 801). This configuration is advantageous for responding to certain size prescriptions of switches. However, the switches of this type do not sufficiently disassociate the movement of the locking device with respect to that of the push rod. 
   SUMMARY OF THE INVENTION 
   It is desirable to produce a safety switch having a reliable lockable drive mechanism and which is of small size but nevertheless allowing certain freedoms of implementation, such as a rotation of the operating head, without changing the state of certain components of the switch. Furthermore, it is desirable to correctly retain the inherent safety function of the switch when extraction forces are applied on the actuator and, if necessary, to be able to unlock the switch whilst the actuator is under load. 
   The purpose of the invention is to respond to these desiderata. 
   According to the invention, the transmission mechanism comprises a pivoting lever capable of assuming a locked position and an unlocked position; the pivoting lever has force applied to it from the push rod such that a movement of translation of the push rod generates a rotation of the lever, and the pivoting lever is provided with a jamming element that is applicable, in the locked position of the lever and transversely with respect to the main axis, against the locking head. 
   The mechanism thus described makes it possible to jam the locking head by a mechanism of small size, with a jamming force that is easy to predetermine. It also makes it possible to unlock the safety switch whilst the actuator is under load. This means that, whilst the actuator is subjected to a considerable force of extraction from the head of the switch, the locking device, in particular the electromagnet, can nevertheless be switched from its locking state to its unlocking state. It is also possible to define the transmission mechanism as comprising a jamming system that is deformable under the effect of the movement of the push rod, this system being provided with a stop for the locking head in the direction of the main axis and with a jamming element applying on the locking head a force that is transverse with respect to the main axis when the actuator tends to be withdrawn from the switch casing. 
   It is advantageous for the lever to be mounted such that it pivots about an axis perpendicular to the main axis and that it is arranged such that the force applied to the locking head is low in comparison with the force undergone by the actuator, in a ratio allowing a movement of the locking head whilst the actuator is under load and following a control to unlock the locking device. 
   The locking head can move in translation along the main axis and the pivoting lever can form a stop keeper for the end of the locking head in the locked position and a bearing slope adjacent to the keeper, the end of the locking head then being applied, in particular under the effect of a spring, against the slope in the unlocked position. 
   The transmission mechanism can comprise a slider mounted in the casing such that it moves parallel, and in particular coaxially, with the main axis, the slider being coupled on the one hand in translation to the push rod and on the other hand by a slot or cam to the pivoting lever. 
   The pivoting lever can for example have the shape of a fork engaged around the slider in order to be applied against bearing rollers provided on a spindle situated at the end of the locking head, a bearing roller being provided at the centre of the spindle in order to be applied on the slider when the bolt applies a lateral thrust. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS. 
     The following detailed description, given with reference to the appended drawings, illustrates an embodiment given by way of example. 
       FIG. 1  is a diagrammatic representation of a safety position switch associated with a dangerous machine. 
       FIG. 2  illustrates a first embodiment of the safety switch according to the invention in the locked state. 
       FIG. 3  illustrates a second embodiment in the unlocked state. 
       FIGS. 4 and 5  show the drive mechanism in the unlocked state and in the locked state respectively. 
       FIGS. 6 and 7  are enlarged views of the detail A of  FIGS. 4 and 5 . 
       FIGS. 8 and 9  are two exploded views in perspective, from the left and from the right respectively, of a part of the safety switch according to the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The safety position switch illustrated in  FIG. 1  comprises in a casing  10  an electrical switch block  11 , in particular a contacts block, and a drive mechanism  12  intended to switch the switch block. The mechanism  12  acts on the block  11  in response to a movement towards or away from the casing (see arrow F 1 ) of an actuator  13 . The actuator is provided with specific mechanical and, if necessary, electronic recognition means and it is for example associated with a protective device  14  (grid, obstacle, etc.) associated with a dangerous machine M. 
   The safety switch has at least one rotating roller  15  or other element provided with shapes appropriate for cooperating with special shapes of the actuator  13  and capable of locking the actuator when the latter is inserted in the casing  10 . The roller  15  is housed in a head  16  of the casing  10  of the switch and acts on a push rod  17  included in the head and capable of assuming, depending on whether or not the actuator  13  is coupled with the roller, a rest position (low position in the figures) or a working position (high position in the figures). The head  16  is mounted on the casing in a rotating manner—in order to allow different orientations of the actuator; the mechanism allows this rotation of the head without changing the state of the contacts of the switch block  11 . 
   The drive mechanism  12  interposed between the push rod  17  and the switch block  11  is lockable, that is to say it can be released or locked by a locking device  20 . This locking device  20  is an electromagnet, a key operated by an operator, a pneumatic device or any other similar driving device (see for example the documents EP 817 227 and FR 2 751 122). When the device  20  is an electromagnet, it comprises a coil  21  and a core  22 , this core being terminated by a locking head  23  which constitutes the locking piece of the mechanism. The locking head  23  locks the mechanism in a single direction, that is to say it prohibits the movement of the push rod from its working position into its rest position, without prohibiting the movement from the rest position to the working position. 
   A control system S is associated with the machine M in order to control its switching on and off (connection Sa); the system S can also receive the “state of the contacts of the block  11 ” information (connection Sb) and can also control the switching of the electromagnet  20  (connection Sc). 
   The drive mechanism  12  comprises, according to the invention, a slider  30  and a pivoting lever  40  forming a system that is deformable under the effect of the movement of the push rod in order to jam the locking head. 
   The slider  30  is mounted on a support, such as a wall of the casing  10  or a base installed in this casing, in order to move in translation along an axis X′ parallel with the main axis X of movement of the push rod  17  (see  FIGS. 2 to 9 ). The casing  10  extends along the direction X, with the disposition of the core  22  of the electromagnet  20  parallel with the axis X of the push rod and, preferably, in alignment with the axis X. The locking head  23  of the core has a spindle  24  that is transverse with respect to X and which carries two lateral rollers  25  and a central roller  26  whose function will be explained below. The slider  30  has a coupling element  31 , such as a finger or a fork, coupled to the lower end of the push rod  17 , preferably in an annular groove of the push rod in order to allow a rotation of the head  16  of the casing, without changing the state of the contacts of the block  11  nor that of the locking system. The coupling element  31  could also be simply applied against the end of the push rod by a spring. The slider  30  has at least one slot  32  or other form of guidance determining the translation of the slider, and cooperating with two fixed guidance spindles  33 ,  34 . Finally the slider  30  has a control pin  35  slightly offset laterally with respect to the axis X′. A lateral face  36  of the slider  30  can be acted upon by the central roller  26  of the locking head  23 , as will be described below. 
   The pivoting lever  40  is associated with the locking head  23  of the locking core  22  which is situated towards the push rod  17 . The pivoting lever  40  has the function of locking the core  22  in its high position (working position) when the actuator  13  is inserted in the head  16  of the casing  10 . The lever  40  is mounted such that it pivots about an axis Y perpendicular to the main axis X and has for this purpose a journal  41  mounted on the fixed spindle  33 , which therefore serves on the one hand as a pivot and on the other hand as a guidance axis for the slot  32 . The axis Y is situated, in the direction X, substantially between the push rod  17  and the locking head  23 . The lever  40  also has an incurved slider  42  for cooperating with the pin  35 . The purpose of the specific shape of the slot is to cause the lever  40  to pivot in an appropriate manner about the spindle  33 . 
   The lever  40  forms a locking arm  43  which is terminated at its free end buy a jamming element  44  intended to apply a transverse pressure on the lateral rollers  25 . The lever  40  forms a stop keeper in which the locking head  23  can become lodged. On the part of the lever situated towards the head  23  there is provided a convex surface or slope  46  against which the head  23  is applied when the locking device  20  is in its unlocked state. 
     FIG. 2  illustrates an embodiment in which the contacts block  11  is actuated directly by the slider  30 , the contacts then reflecting the state of the actuator. The block  11  can also be actuated directly by the push rod  17 .  FIG. 3  shows an embodiment in which the contacts block  11  is actuated from the core  22 , the contacts then reflecting the state of the electromagnet. 
   The functioning of the switch will now be explained with reference to  FIGS. 4 to 7 . 
   In the case illustrated in  FIGS. 4 and 6 , the actuator  13  is withdrawn from the head  16  of the switch, such that the push rod  17  is placed in the low position. The slider  30  coupled to the push rod is also put in the low position and, via the pin  35 , pushes the lever  40  in the anticlockwise direction into the unlocked position. This means that the core  22  of the electromagnet, shown in the low position in  FIGS. 4 and 6 , is in an unlocked state. Depending on the case, this state corresponds to the energized case or non-energized case of the coil  21  of the electromagnet  20  (in the latter case, the core  22  is pushed upwards by a spring and remains in equilibrium against the lower surface  46  of the lever  40 ). 
   In order to change to the state illustrated in  FIGS. 5 and 7 , the actuator is engaged in the head  16  of the switch, and the push rod  17  rises whilst driving the slider  30 . By means of the pin  35 , the slider  30  forces the lever  40  to pivot in the clockwise direction until it reaches the position shown in  FIGS. 5 and 7 . If the coil  21  is (or remains) energized, the core  22  remains in the low position. If the coil  21  is (or remains) non-energized, the lower surface  46  of the lever slides over the rollers  25  of the core  22  and then the rollers  25  become engaged in the space located between the jamming elements  44  and the lateral face  36  of the slider  30  and remain lodged against the top stop in the keeper  45  formed by this space. Any force applied to the actuator to extract it from the head  16  of the switch brings about a jamming effect of the elements  44  on the locking head  23 , which becomes greater as the extraction force becomes stronger; the force cannot damage the electromagnet since the roller  26  carried by the spindle  24  of the locking head  23  is applied against the lateral face  36  of the slider  30 . The resultant force is thus taken up by the guidance of the core and, via the spindles  33 ,  34 , by the casing. 
   It is appropriate to observe that the lever arms “pivot  33 -pin  35 ” and “pivot  33 -locking elements  44 ” are mutually determined in such a way as to greatly reduce the force imparted to the core as a result of action by the actuator in the direction of extraction and thus makes it possible to unlock the locking device whilst the lever  40  is clamped on the locking head  23 . 
   The shown switch allows a rotation of the head  16  with respect to the rest of the casing without changing the state of the contacts of the switch block  11  nor the state of the drive mechanism nor that of the locking device. 
     FIGS. 8 and 9  show, in an exploded manner, the component parts of the drive mechanism  12  and illustrate in particular the guidances provided in the head  16  for the push rod  17  and in the main part of the casing  10  for the core. In particular, there can be seen the rollers  25  and  26  mounted on the spindle  24  which is associated with the locking head  23  and the embodiment of the pivoting lever  40  as a fork engaged around the slider  30 , each branch of the fork acting on a roller  25  disposed on the spindle  24 .