FR2766750A1 - PILOT CLAMPING DEVICE - Google Patents

Abstract

A single actuator (31, 11) moves linearly, a first crew (11-15) along guide lights (202) in a second crew (20-23), and the second crew along guide lights (303 ) in a body (30) of the device. The first crew contains fingers (13) which are taken out with a pilot element (21) of the second crew passing through a hole (TR) in sheets (T1, T2) to be clamped in order to be welded. While the second crew is immobilized by tweezers (33), the first crew (11-15) is retracted into the body so that the fingers pivot around an axis (15) towards the outside of the pilot element and jaws (135) clamp the sheets onto the body. The two crews entered the body together thanks to an overtravel of the first crew to link it to the second crew by tweezers (23).

Description

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  Pilot clamping device The present invention relates generally to devices for moving at least alternately one or more elements back and forth. More particularly, it relates to a compact pilot clamping device, in particular electrical, for positioning, centering, clamping or holding at least one part to be worked, treated or transported. This type of pilot clamping is used, for example, to clamp sheet metal

  chassis in automobile assembly lines.

  Conventional clamping or clamping heads are generally associated with a double-acting hydraulic or pneumatic cylinder housed in a housing on which a clamping arm is mounted in rotation, the arm being controlled in rotation by the jack between a clamping position and a release position by means of a rod sliding between two extreme positions. The transformation of the reciprocating movement of the rod into a rotational movement of the

  arm is made using an articulated linkage.

  Clamping heads of this type are also known with a relatively large size. The clamping which results from such tools is due to a pendulum movement of the clamping arm which, in the case of certain parts to be treated, can lead to a malfunction of said clamping arm and, consequently, a bad clamping of the part. This can then lead to safety problems, as a work piece or several pieces to be treated are not properly tightened and maintained.

together.

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  The structure of these known clamping heads is also relatively complex. In addition, the actuation being carried out using hydraulic or pneumatic cylinders, it is not possible to control the stroke of the clamping arm, which most often results in a relatively sudden movement of the clamping arm during tightening which can cause danger to users and

defects on the parts to be tightened.

  The French patent application filed on October 25, 1996 under N 9613036 and not published describes a pilot clamping device comprising first and second mobile equipment. The first mobile assembly comprises a yoke and two clamping elements, such as fingers, pivoting in opposition in the yoke and is moved linearly by a first motor. The second equipment comprises a sheath sliding in the body of the device and in which the yoke slides, and a pilot element from which the clamping elements can protrude by pivoting in order to clamp two sheets against the part.

upper body.

  The second crew is moved by a second motor to move the two crews, including

  with the first engine, in the body.

  When using the pilot clamping device, the second crew with the first crew is first moved linearly so that the pilot element projects out of the end of the body of the device and engages in a hole in the sheets to be clamped. Then the first motor is actuated to make the first crew and particularly the elements slide in the opposite direction from the previous

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  clamping element in the pilot element so that the clamping elements pivot from an extreme loosening position to an extreme clamping position in which the sheets are pressed against the upper part of the body. In order to clamp the sheets through which the pilot element passes, the clamping elements are driven in linear displacement independently with respect to the pilot element, towards the extreme clamping position, that is to say

that they are brought back to the body.

  The pilot clamping device thus comprises two electric motors, and is therefore heavy,

bulky and expensive.

  The present invention also aims to overcome the drawbacks of the clamping heads by providing a method of linear displacement of two crews overcoming the disadvantage of the second motor for

move the first motor.

  To this end, a method for linearly moving a first crew between two first positions relative to a second crew, and the second crew between two second positions relative to a fixed body, is characterized in that the first and second crews are movable by a common actuator, the first and second crews can be moved together from one of the second positions to the other, the second crew is stationary in the body at one of the second positions when the actuator moves the first crew between the second positions , the first crew can be moved from one of the first positions to one of the third positions at which the first and second

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  crews are provisionally linked together, the second crew being stationary in the body at said a second position when the first crew is untied from the second crew to the other of the third positions and is moved from said other third position to said a second position. The invention also relates to a device for implementing the method according to the invention, comprising a first crew, and a second crew movable in a body. The device, such as a clamping device, is characterized in that it comprises a single actuator, first connecting means for detachably linking the first and second crews so that the actuator moves the first and second linearly together crews in the body, and second connecting means for detachably connecting the second crew to the body so that the actuator linearly displaces only the first crew in the second crew

motionless in the body.

  The actuator is only linked to the first crew so that the movements of the second crew can be carried out so that the first crew pushes the second crew without being linked to the first crew from one of the second positions and pulls the second crew being provisionally linked to the first crew of one towards

the other of the third positions.

  Preferably, the only actuator is a jack

  electric having a screw fixed to the first crew.

  The single actuator makes the device according to the invention more compact, such as a device for

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  pilot tightening, and contributes to a reduction in sound

weight and cost.

  Strokes in the opposite direction of the first crew between said a first position and said a third position and between said other third position and said a second position, intended only to link and untie the first and second crews are preferably substantially equal and significantly shorter that the substantially equal strokes of the first and second crews together between said first positions and between said third positions, intended to remove a pilot element from the body of the device and to bring back jaws situated at the ends of clamping elements against parts, sheets or the like to be tightened. The travel of the pilot element, and therefore of the second crew, is limited to said second positions at which the second crew is brought into abutment against the body in opposite directions. The body of the device then includes two stops to limit the linear movement of the

second crew.

  The first crew in said third position can be abutted against the second crew in order to link the first crew to the second

  crew already abutted against the body.

  The first connection means may include a first projection in one of the first and second crews, and a first elastic retention means fixed to the other of the first and second crews to retain said first projection as long as the actuator does not exercise no effort greater than a first predetermined value for

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  separate the first projection from the first retention means. According to a preferred embodiment, the first assembly comprises a piston linked to the actuator, at least one pivoting clamping element, and a hinge pin between the piston and the clamping element, the first projection being one end of

the axis of articulation.

  The second connecting means may have structure and arrangement similar to the first means

  to reduce manufacturing costs.

  In this case, they comprise a second projection in one of the second equipment and body, and a second elastic retention means fixed to the other of the second equipment and body to retain said second projection as long as the actuator does not exert force greater than a second predetermined value to separate the second projection from the second retention means. According to a preferred embodiment, the second projection is one end of a pin passing through a lumen of a clamping element in the first crew, and having a portion parallel to the direction of linear movement of the crews and a portion, for example curvilinear, secant to said direction of travel

linear.

  In order to further reduce the number of mechanical parts, the pin passes through the pilot element of the second assembly in which the clamping element slides pivotally and which is in abutment against the body when said pin is retained by the

  second means of elastic retention.

  In the previous embodiments, it is important that the first predetermined value of effort is higher than the second predetermined value of effort so that the second crew

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  either linked to the body during the movement of the only first crew and is untied from the body while remaining linked to the first crew in order to pull the first and second crews together and thus enter the pilot element with the element

Clamping.

  According to a preferred embodiment, each of the first and second elastic retention means is a tweezer. For example, a tweezer is attached to one end of a lumen in which the axis

  joint or the pin is moved.

  Other characteristics and advantages of the present invention will appear more clearly on

  reading the following description of several

  preferred embodiments of the invention with reference to the corresponding appended drawings in which: - Figures 1 and 2 are axial sectional views and partially in section taken along two perpendicular axial planes of a pilot clamping device according to the invention at a first low position of first and second mobile equipment inside the device; - Figure 3 is a detailed front view of two pivoting fingers, corresponding to the position shown in Figure 2; - Figures 4A and 4B are timing diagrams of the cycle of ascent and descent of the first and second moving parts, respectively; - Figures 5 and 6 are views similar to Figures 1 and 2 of the pilot clamping device according to the invention with the two moving parts in a second high position; - Figures 7 and 8 are views similar to Figures 1 and 2 of the pilot clamping device according

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  the invention with the first crew in an intermediate clamping position and the second crew in the high position shown in Figures 5 and 6; - Figure 9 is a detailed front view similar to Figure 2, of the two articulated fingers after pivoting for tightening in correspondence with Figures 7 and 8; - Figures 10 and 11 are views similar to Figures 1 and 2 of the pilot clamping device according to the invention with the first crew in a fourth highest position and the second crew in the second high position shown in Figures 5 and 6 ; and - Figures 12 and 13 are views similar to Figures 1 and 2 of the pilot clamping device according to the invention with the first crew in a lower position somewhat higher than that shown in Figures 1 and 2 and the second crew at the

  low position shown in Figures 1 and 2.

  A pilot clamping device according to the invention essentially comprises a set of fixed parts 3 and first and second sets of moving parts 11-15 and 20-23. These parts are first described with reference to Figures 1 and 2 in which the device has a longitudinal axis of symmetry YY which is located for example vertically so as to clamp at least two sheets T1 and T2 which are positioned horizontally in device head. In FIGS. 1 and 2, the moving parts are assumed to be stationary at a first low position P1. Stroke lengths are given below by way of nonlimiting example in the case of the tightening of two or more sheets

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  together having a thickness E of less than approximately 15 mm. The first mobile assembly 11-15 essentially comprises in the lower part a cylindrical piston 12 connected to a motor screw 11, and in the upper part a pair of clamping elements, such as pivoting clamping fingers 13, as well

than two pins 14 and 15.

  The second movable element 20-23 surrounds the first element and essentially comprises in the lower part a cylindrical sheath 20 and in the upper part a pilot element 21, as well as a

pair of elastic tweezers 23.

  The set of fixed parts essentially comprises a hollow cylindrical body 30, a single motor 31, a support part 32 and a pair

elastic tweezers 33.

  The body 30 contains in the lower part the motor 31 which is an electric actuator which can be controlled automatically through a connection terminal 300 so that the first mobile assembly is moved according to a cycle of four up and down strokes M2, D3, M41 + M42, D5 + Dl, as will be seen below with reference in particular to FIG. 4A. The forces of the electric actuator are more easily and precisely modifiable during a cycle than with a hydraulic or pneumatic actuator. The electric actuator is an actuator of the screw / nut type, the screw 11 of which is stationary in rotation and movable in translation along the axis YY. The electric actuator maintains the positions of the moving parts in the event of

power outage.

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  The support piece 32 is a cylindrical ring slidingly surrounding the pilot element 21 and having a flange fixed by screws 321 on the upper end face of the body 30. Between the upper face 311 of the motor housing from which motor screw 11 protrudes, and the support piece 32, the interior of the body 30 comprises from bottom to top, a recess 301 and a long bore 302. The recess 301 allows the second crew to race M2. A lower collar 201 of the sheath 20 of the second crew is mounted with clearance in the recess 301. The bore 302 extends below the support piece 32 over a length substantially equal to that of the sheath. The sheath body 20 and a lower flange 211 of the pilot element 21 are slidably mounted

in bore 302.

  In the upper part of the body 30 are formed two substantially rectangular longitudinal slots 303, diametrically opposite. Ends of the pin 22 of the second assembly project diametrically at the upper end of the sheath 20 and are guided in the slots 303. The length of the slots is substantially greater than the sum of the diameter of the pin 22 and the length of travel of rise / fall M2 = D5 of the second crew. The 303 lights are closed from the outside by a thin protective cover

  cylindrical 304 held by the support piece 32.

  The tweezers 33 are housed diametrically

  opposite the upper ends of the lights.

  Each tweezer 33 has a profile substantially in uppercase omega Q. The circular upper head 331 of the tweezers bears against the upper end of the respective lumen 303 and has a diameter substantially larger than that of the pin 22, it 2766750

  which is bigger than the crotch 332

  next to the head when the tweezers 33 is at rest.

  Feet 332 of the tweezers 33 are supported substantially perpendicular to the axis YY of the tweezer legs 332 and the body 30 in two

  machining opening into the respective lumen 303.

  A plane support boss 305 provided with tapped holes 306 extends laterally on the body 30 to fix the device by screws on a plate which, for example, supports other pilot clamping devices according to the invention for clamping the sheets Tl and T2 at other holes, and / or other automata, such as welders, drills, etc. In the first assembly, the main parts constituted by the piston 11 and the pair of fingers 13 are located respectively in the lower part and in the upper part inside 301-302 of the body and are respectively mounted with axial sliding in the sheath 20 and pivoted in the pilot element 21 of the second crew. In a axial blind hole with deep counterbore 121 made from the underside of the cylindrical piston 12 penetrates a smooth end of the engine screw 11 which is linked in translation and rotation to the piston by the

diametrical pin 14.

  The upper part 122 of the piston 12 is in the form of a yoke and has an axial groove in which are pushed in sliding and side by side the rounded lower ends 131 of the fingers 13. The second pin 15 passes diametrically in sliding the branches of the yoke 122 and the

  lower fingertips 131.

  The ends of the pin 15 projecting from the yoke 122 are guided in translation parallel to

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  the YY axis in two substantially rectangular longitudinal openings 202, diametrically

  opposite, formed in the sheath 20.

  At the upper end of each guide lumen 202 is housed one of the two elastic tweezers 23. Like the tweezers 33, the tweezers 23 has a profile substantially in omega capital Q, a circular upper head 231 which has a substantially larger diameter. to that of the pin 15 and which bears against the enlarged upper end of the respective lumen 202, and of the feet 233 bearing perpendicularly in two machining operations perpendicular to the axis YY and opening into the

respective light 202.

  The tweezers 23 has substantially the same shape as the tweezers 33 but its thickness is greater. The tweezers 23 thus oppose a much higher flexural strength than the tweezers 33, in a ratio of 1 to 6; typically, the stop pin 22 must be pushed under an effort of at least about 5 daN to spread the crotch 332 and pass through the head 331 of the tweezers 33, while the pin 15 must overcome an effort of at least 30 daN approximately to spread the crotch 232 and pass through the head 231 of the tweezers 23. As will be seen below, this difference in pinches between the tweezers 33 and 23 allows: (i) the descent D3 and the ascent M41 of the first crew 11-15 after the exit of the pilot element 21 and the holding in the upper position of the second crew 20-23 as shown in Figures 6 and 8, and thus authorize the descent D3 of the first crew only when the pin 22 is clipped into the tweezers 33, and

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  (ii) provisionally connect the piston 12 and the sheath 20 and therefore the two crews together in translation after the rise M42 of the pin 15 in the tweezers 23, as shown in FIG. 11, and to pull them together down during the next descent D5, as shown in figure 13, in

  detaching the pin 22 from the tweezers 33.

  The lower ends 131 of the fingers 13 are pivotally mounted around the pin 15, while the slots 132 of the fingers 13 extending substantially longitudinally in the middle of the fingers

  are slidably mounted around the pin 22.

  Each finger lumen 132 has a longitudinal profile which constitutes an active surface relative to the section of the pin so as to transform the translation of the first crew in descent D3 and climb M41, as shown in FIGS. 5 to 11, into a pivoting of the finger respective 13. The light 132 comprises a short rectilinear short portion 133 and a long curvilinear upper portion 134. The short position 133 extends parallel to the axis YY and radially to the respective finger hole crossed by the articulation pin 15, and has a length at least equal to the climb stroke M42 of the first crew so that the pin 15 is forced into the heads 231 of the lower tweezers 23, as shown in FIG. 11. The upper long portion 134 of the light 132 intersects at the axis YY is curved in a direction opposite to the pivoting sought for the respective finger, that is to say the light is curved towards the right of the axis YY for the finger to pivot the left, and vice versa, as shown in FIG. 3. The length of the upper long portion of light 134 is substantially equal to each of the descent and ascent races D3

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  and M41 of the first crew to pivot the fingers 13 in opposite directions so that they are deployed out of the pilot element 21 and tighten the sheets T1 and T2, then then to pivot the fingers respectively in opposite directions to the previous ones for

release the sheets.

  The major part of the body of each finger 13 extends in a long longitudinal groove 212 of the pilot element 21, open from the pin 22 rigidly connecting the sleeve 20 and the pilot element, to the nose 213 of the element pilot. The nose is frustoconical to facilitate the crossing of a hole TR in the sheets T1 and T2 by the pilot element and

  accept berthing faults on the sheets to be clamped.

  The fingers are terminated by jaws 135 substantially perpendicular to the bodies of the fingers

to tighten the sheets.

  In FIG. 1, the upper screed end 122 of the piston 12 is at the distance M42 from the lower end 210 of the pilot element 21, and the finger jaws 135 are at a distance substantially greater than the length of stroke M42 from the bottom of the groove 212 in the pilot element nose 213 so that the first crew 11-15 can still be mounted from M42 for the clipping of the pin 15 in the lower tweezers 23, as

shown in Figures 10 and 11.

  The operating cycle illustrated in diagram form in FIGS. 4A and 4B is now described with reference to five successive positions P1 to P5 of the first crew 11-15 illustrated in the figures

1-2 to 12-13.

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  At rest, prior to a first stage of the pilot clamping device cycle, as shown in FIGS. 1 and 2, the superimposed sheets Tl and T2 are positioned on the support piece 32 so that one TR of their holes is centered on the nose 213 of the pilot element 21 which protrudes about 5 mm from the upper face of the support piece. According to other variants, the sheets are positioned after the rise M2 of the pilot element 21. In the initial position Pl shown in FIG. 1, the engine screw 11 is as low as possible, with the underside of the piston 12 abutting against the upper face 311 of the motor housing 31. The stop pin 22 has its ends abutting against the lower ends of the slots 303 in the body, and consequently the second crew 20-23 is at the lowest position Pl, the sleeve 20 being almost completely contained in the lower recess 301, and the pilot element 21 being almost

  completely contained in the bore of body 302.

  The articulation pin 15 is located between the legs 232 of the lower tweezers 23, just below the natural narrowing at the base of the tweezer heads 231. Jointly, the pin 22 crosses zones between the lower rectilinear short portions and long upper curvilinear portions. of light 133 and 134 of the fingers 13, at a distance of at least M41 and M42 respectively from the upper and lower ends of the lights 132. The positions of the fingers 13 above the piston are completely contained in the groove 212 of the pilot element , the fingers are "aligned" along the YY axis and the 135 finger jaws are

  at least at the distance M42 from the bottom of the groove 212.

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  At the first cycle step P1-P2, the screw of the motor 11 is mounted by M2 = 35 mm to reach the position P2 shown in Figures 5 and 6. During this rise, thanks to the pin 15 wedged in the crotch 232 tweezers 23, the piston 12 pushes up the sheath 20 permanently linked to the pilot element 21 until the ends of the pin 22 are introduced into the heads 331 of the upper fixed tweezers 33 and the lower collar 201 the sleeve abuts against a shoulder 307 between the recess 301 and the bore 302. The thrust exerted upwards by the motor screw 11 is greater than a second predetermined value by at least about 10 daN and sufficient to overcome the pinching of the tweezers 33 and make the crotch 332 of the tweezers 33 pass through the ends of the pin 22, but is much lower than a first predetermined value and insufficient

  to overcome pinching tweezers 23.

  During the climb M2 from P1 to P2, the first and second crews are thus translated together, without relative displacement between them, the first pushing the second. Pilot element 21 is out

maximum body 30.

  At a second cycle step P2-P3, the engine screw 11 is lowered from (D3-E) so that the first mobile assembly 11-15 reaches a third position P3 intermediate between positions Pl and P2, as shown in FIGS. 4A , 7, 8 and 9. The second crew 20-21 remains stationary at position P2, as indicated in FIG. 4B; pinching heads

  of pincers 331 retaining the pin 22.

  During the descent (D3-E), the walls of the upper curvilinear portions 134 of the lights of

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  finger 132 slide on the central portion of the stationary pin 22 which, on the opposite side, pivots the fingers 13 around the pin 15. The opposite pivoting of the fingers progressively spreads the jaws 135 while approaching the sheets T1 and T2, so to bring them one against the other and tighten them against the support piece 32. The thrust exerted by the jaws 135 from above the sheets deflects, if necessary, sheets slightly veiled in the vicinity of the hole TR. The descent D3-E thus has a length equal to the difference of the axial length D3 = 20 mm of the upper long light portions 134 and of the total thickness E of the sheets T1 and T2 typically less than about 15 mm. At the end of the descent stroke D3, the ends of the hinge pin 15 do not reach the lower ends of the sheath slots 202. If the clamping works without sheet metal to be clamped, the jaws 135 of the fingers press on the workpiece. support 32. The upper ends of the finger slots 132 have play with respect to the pin 22. The pin 15 has play with respect to the lower ends of the

scabbard lights 202.

  Between the second and third cycle stages, the tight sheets Tl and T2 are welded together or

  undergo any other specific treatment.

  The third cycle step comprises two consecutive ascents M41-E and M42 from the first crew 11-15 from the intermediate position P3 to the highest position P4 shown in FIGS. 10 and 11, the second crew 21-23 still remaining stationary in the position

P2.

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  The length of the rise M41-E <20 mm is equal to that of the previous descent D3-E so that the engine screw 11 pushes the first crew upwards until it returns to the position P2, as shown in the figures 5 and 6. The jaws 135 are released from the sheets Tl and T2 and the fingers 13 pivot respectively in opposite directions to those during the descent D3 so as to be folded down completely

  in the axial groove 212 of the pilot element 21.

  From position P2, the first crew 11-15 can be pushed upwards since the collar 201 of the sleeve 20 is applied against the shoulder of the

body 307.

  On the other hand, from position P2 to position P4 at which the piston yoke 122 abuts against the lower end 210 of the pilot element 21, the first assembly 11-15 is pushed upwards over a length M42 = 5 mm thanks to a high force exerted by the motor screw 11 greater than the first predetermined value of at least about 60 daN and sufficient to overcome the pinching exerted by the narrowing between legs 232 and heads 231 of the elastic tweezers 23, which connects the two crews 11-15 and 20-23. During the short climb M42, rectilinear lower portions 133 of the finger slots 132 slide on either side of the upper stationary pin 22. The fingers 13 do not pivot during the climb M42. The jaws 135 are brought closer to the bottom of the groove 212 in the pilot element 21 which is still kept out of the

device body 30.

  At the fourth cycle step, the engine screw 11 is lowered following a stroke D5 = 35 mm and pulls the two crews down together, and

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  particularly the second crew 20-23 towards the initial position P1, shown in FIGS. 1 and 2, until the ends of the pin 22 abut against the lower ends of the body openings 303, in a direction opposite to the stop of the sheath collar 201 against the body shoulder 307 at the end P2 of the first step. At the start of the descent D5, the traction exerted by the motor screw 11 is higher than the second predetermined value of force to overcome the pinching of the stop pin 22 exerted by the fixed tweezers 33 in order to remove the pin 22 from the tweezers 33, and is lower than the first predetermined force value and therefore insufficient to separate the hinge pin 15 from the tweezer heads 231 which keeps the two crews together. At the end of the descent D5, the nose 213 of the pilot element 21 containing the folded fingers 13 is again at the level of the sheets Tl and T2 which at this stage can be removed. Due to the previous climb M42 to connect the two crews through the hinge pin 15, the position P5 of the first crew 11-15 at the end of the descent D5 is higher by M42 = Dl = 5 mm than the position P1 of the first crew, as shown in

Figure 4A.

  At the end of the cycle, following the descent D5, or according to another variant at the start of the cycle, before the rise M2, the motor screw 11 is lowered from Dl and exerts on the first crew 11-15 a pull down high greater than the first predetermined force value corresponding to the pinching exerted by the tweezers 23 on the ends of the hinge pin 15. This

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  traction causes the pin 15 to come out of the tweezer heads 231 towards the crotch 232 of the tweezers 23 and also the separation of the first crew 11-15 and the second crew 20-23, the ends of the pin 22 of which are held in abutment against the lower ends of body lumens 303 in the direction of pull

exercised downward.

  The invention is not limited to the preferred embodiment described above. According to other variants, the jaws of the finger can be replaced by other tools, and the relative movement of the fingers can be modified by modifying the layout of the lights 132. The pilot element and the fingers are interchangeable so as to adapt them in various dimensions and sections for example, cylindrical, oblong or square, of the hole in the

parts to be clamped.

  A means to temporarily immobilize the

  first crew 11-15 in the second crew 20-

  23 and a means for temporarily holding the second assembly 20-23 temporarily in the body 30 may be other than assembling a tweezer 23 with one end of the pin 15 and assembling a

  tweezers 33 with one end of the pin 22.

  Naturally, equivalent and "reverse" assemblies to the preceding ones may be suitable, comprising for the first, a tweezer fixed to the piston 12 and a radial lug in the sheath 20, and for the second, a tweezer fixed to the sheath 20 or to the pilot element 21 and a radial lug in the

body 30.

  According to another variant, at least one of the elastic stationary assemblies with tweezers and pins

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  is replaced by an assembly between a radial spring housed in the first, respectively, the second equipment, and a ball or any equivalent equivalent piece pushed by the spring into a housing provided in the second equipment, respectively the body, or is replaced by a reverse assembly to the previous one.

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Claims (14)

  1 - Method for linearly moving a first crew (11-15) between two first positions (P2; P3) relative to a second crew (20-23), and the second crew (20-23) between two second positions (P1, P2) relative to a fixed body (30), characterized in that the first and second crews (11-15; 20-23) are movable by a common actuator (31,11), the first and second crews are movable together one (Pl) towards the other (P2) of the second positions, the second crew (20-23) is stationary in the body at one (P2) of the second positions when the actuator moves the first crew (11 -15) between the second positions (P2, P3), the first crew (11-15) can be moved from one (P2) of the first positions to one (P4) of third positions (P4, P5) at which the first and second crews (11-15,20-23) are provisionally linked together, the second crew (20-23) being stationary in the e body (30) in said a second position (Pl) when the first crew is untied from the second crew to the other (P5) of the third positions and is moved from said other third position (P5) to said a second position (Pl).   2 - Process according to claim 1, according to which the actuator (31,11) is linked only to the first crew (11-15).   3 - Process according to claim 1 or 2, according to which the first crew (11-15) pushes the second crew without being linked to the first crew 23 2766750   from one (Pl) to the other (P2) of the second positions and pulls the second crew by being linked to the first crew from one (P4) to the other (P5) third positions.   4 - Process according to any one of   Claims 1 to 3, according to which races in   opposite direction (M42, D1) of the first crew (11-15) between said a first position (P3) and said a third position (P4) and between said other third position (P5) and said a second position (Pl) are substantially equal and significantly shorter than the substantially equal strokes (M2, D5) of the first and second crews together (11-15, 20-23) between said first positions (P1, P2) and between said third positions (P4, P5).   - Process according to any one of   claims 1 to 4, according to which the second   crew (20-23) is at said second positions (P1, P2) abutted against the body (30) according to opposite directions.   6 - Process according to any one of   claims 1 to 5, according to which the first   crew (11-15) at said one third position (P4)   is abutted against the second crew (20-23).   7 - Device for implementing the method   according to any one of claims 1 to 6,   comprising a first crew (11-15), and a second crew (20-23) movable in a body (30), characterized in that it comprises a single actuator (31,11), first connecting means 24 2766750   (15,23) to detachably link the first and second crews so that the actuator linearly moves the first and second crews together in the body, and second connecting means (22,33) to detachably link the second crew (20-23) to the body so that the actuator linearly displaces only the first crew (11-15) in the second crew   (20-23) immobile in the body (30).   8 - Device according to claim 7, wherein the body (30) comprises two stops (307,303) to limit the linear movement of the second crew (20-23).   9 - Device according to claim 7 or 8, wherein the single actuator (31,11) is an electric actuator having a screw fixed to the first crew (11-15).   - Device according to any one of   claims 7 to 9, wherein the first means   of connection comprise a first projection (15) in one (11-15) of the first and second crews, and a first elastic retention means (23) fixed to the other (20-23) of the first and second crews for retain said first projection (15) as long as the actuator does not exert a force greater than one first predetermined value.   11 - Device according to claim 10, wherein the first assembly comprises a piston (12) linked to the actuator (31,11), at least one pivoting clamping element (13), and a hinge pin (15 ) between the piston and the clamping element, said 2766750   first projection being one end of said axis articulation (15).   12 - Device according to any one of   claims 7 to 11, wherein the second   connecting means comprise a second projection (22) in one (20-23) of the second equipment and body, and a second elastic retention means (33) fixed to the other (30) of the second equipment and body to retain said second projection (22) as long as the actuator exerts no force greater than   a second predetermined value.   13 - Device according to claim 12, wherein said second projection is one end of a pin (22) passing through a lumen (132) of a clamping element (13) in the first crew, and having a portion (133 ) parallel to the direction of linear movement of the crews and a portion (134) intersects said direction.   14 - Device according to claims 11   and 13, in which said pin (22) passes through a pilot element (21) of the second assembly in which the clamping element (13) slides pivotally and which abuts against the body (30) when said pin (22) is retained by the second means of elastic retention (33).   15 - Device according to claim 10   or 11 and any one of claims 12 to   14, in which the first predetermined force value is higher than the second value predetermined effort. 26 2766750   16 - Device in accordance with any of   claims 10 to 15, wherein the means of   elastic retention is tweezers (23,33).