Patent ID: 12246437

DETAILED DESCRIPTION OF THE INVENTION

FIGS.1-5show a first embodiment100of the gripper for industrial manipulators according to the present invention.

The gripper100comprises a body101inside which a cylinder102having an air piston103movable therein is defined, according to a typical cylinder-piston coupling. Compressed air is supplied through the nozzle105. The gripper comprises two jaws106and107fitted to the body by means of pins108and109, so as to be able to pivot between an open position, at which the jaws106,107are spread out as shown inFIGS.1,2and5, and a closed position, at which the jaws106,107are in abutment against each other as shown inFIG.3.FIG.4shows an intermediate position between the open position and the closed position, which can be defined piece gripping position, with the jaws106,107slightly spread out and closed against a piece P to be handled.

The closing movement of the jaws106,107is caused by the piston103that has a wedge-shaped portion110which gets in between the jaws106,107when the compressed air is supplied through the nozzle105and the piston103moves towards the end of the cylinder102closest to the jaws106,107themselves, i.e. it moves towards the point that can be called closure dead point. Precisely to achieve the closure, the jaws106,107are equipped with shoulders106′ and107′ (which can also be defined proximal ends) extending from the respective pins108,109towards the wedge-shaped portion110of the piston103, on the opposite side with respect to the distal ends106″ and107″ which have the function of picking up and holding the pieces P.

A resilient element111, such as a spring or rubber element, is inserted between the jaws106,107to cause the gripper to automatically open when the piston103returns to its initial position, i.e. when the compressed air supply is suspended. The spring111exerts a thrust that tends to spread out the distal ends106″ and107″ of the jaws106,107, i.e. it tends to return the jaws106,107to the open position when the thrust exerted by the wedge-shaped portion110of the piston103stops.

In the example shown in figures, the spring111acts along a direction orthogonal to the longitudinal direction along which the piston103is displaced.

The gripper100comprises a sensor denoted as a whole by the numeral112, whose function is to generate an electrical signal indicating the position taken at any given moment by the jaws106,107. Unlike the solutions known in the art, in the gripper100the sensor112is not positioned on board the piston103or on the distal end106′,107′ of one of the jaws106,107; the sensor112is functionally interposed between the piston103and one of the jaws106,107, in particular between the wedge-shaped portion110of the piston103and the shoulder106′,107′ of one of the jaws106,107.

In the example shown inFIGS.1-5, the sensor112is interposed between the wedge-shaped portion110of the piston103and the shoulder106′ of the jaw106.

The sensor112is of magnetic type and now its structure and operation will be described in detail.

Turning toFIG.5, the sensor112comprises a first portion113intended to be fixed to the shoulder106′ of the jaw106in order to be stationary with respect to the latter; in other words, the first portion113of the sensor112is intended to rotate fixedly with the shoulder106′ with respect to the pin108. In the example shown, the first portion113of the sensor112has protrusions114that snap into corresponding holes115obtained on the shoulder106′ of the jaw106.

On the portion113of the sensor112there is an electronic circuit116able to detect, by Hall effect, the presence of a magnetic element at a given distance. In order to power the electronic circuit116and to collect the electrical signal generated by the sensor112, wiring117is provided.

The sensor112also comprises a second portion118, which can be defined sliding block, pivotally constrained to the first portion113, thanks to a pin119inserted through the shoulder106′ of the jaw106and through both the first portion113and the second portion118of the sensor112. In other words, the second portion118of the sensor112is hinged to the first portion113by means of the pin119.

Thanks to this configuration, the second portion118is movable with respect to the first portion113, and therefore also with respect to the shoulder106′ of the jaw106, between a distal position, corresponding to the maximum possible angle between the two parts, and a proximal position, corresponding to the minimum possible angle between the two parts113and118.

As best shown inFIG.5, a magnetic element120, shaped like a pellet, is housed in a dedicated seat120′ in the second portion118. Since the magnetic element120moves fixedly with the second portion118, the detection of the position of the magnetic element120by the electronic circuit116fitted on board the first portion113of the sensor112corresponds to indirectly measure the angular position of the second portion118, which in turn depends univocally on the position taken by the jaw106at the time of detection. The second portion118is always in abutment against the wedge-shaped portion110of the piston103, acting as a sliding block on the respective surface, and for this reason the second portion118of the sensor112preferably has a rounded surface to facilitate the sliding of the piston103on the wedge-shaped portion110.

An elastic element121, preferably a spring, is functionally interposed between the two portions113and118of the sensor112, so as to constantly exert a thrust that tends to move the second portion118away from the first portion113. It is right the piston103that, when moving towards the respective closure dead point, counters the spring121by slotting in between the shoulders106′ and107′ of the jaws106and107and thus limiting the relative movement of the second portion118with respect to the first portion113of the sensor112.

In other words, when the gripper100is activated and the piston103is thrust by the compressed air, the piston103itself exerts a thrust on the second portion118of the sensor112, thereby counteracting the force exerted by the spring121. If a piece P is gripped, the new angular position taken by the jaw106causes the second portion118to pivot on the pin119and the angle between the parts113and118to correspondingly decrease; in this circumstance the electronic circuit116detects the approach of the magnetic element120. When a given relative position of the magnetic element120is reached, i.e. when the electronic circuit116detects that the flux intensity of the magnetic field generated by the magnetic element120reaches a threshold value, corresponding in practice to an univocal angular position of the portion118of the sensor112and, therefore, corresponding to the situation of the piece having been gripped, the sensor112generates a corresponding signal.

If the gripper100accidentally loses the piece P, or the latter is not gripped at all, the piston103stops against a limit stop122(closure dead point), without causing the elastic element121to be compressed, and therefore without generating the signal corresponding to the piece P having been successfully gripped. For example, inFIG.4the portion110of the piston103is not in abutment against the limit stop122, as is conversely shown inFIG.3.

In particular,FIG.2shows the gripper100with the jaws106,107completely open: the angle between the second portion118and the first portion113of the sensor112is maximum and the magnetic element120is at the maximum distance from the electronic circuit116.FIG.3shows the gripper100with the jaws106,107completely closed: the angle between the second portion118and the first portion113of the sensor112is maximum and the magnetic element120is at the maximum distance from the electronic circuit116.FIG.4shows the gripper100with the jaws106,107in the intermediate gripping position of the piece P: the angle between the second portion118and the first portion113of the sensor112is minimum, and the magnetic element120is in the position closest to the electronic circuit116precisely because of the angular displacement of the jaw106from the closed position.

By adopting the solution just described, the industrial manipulator is able to determine without errors that the piece P has possibly fallen or that it has not been gripped. In both cases, the consent of the sensor112fails and the manipulator stops, i.e. the gripper100is stopped.

The solution described provides several advantages.

First of all the space around the jaws106,107remains completely free: the sensor112is not fitted to a distal end106″ or107″ of the jaws106,107, i.e. it is not fitted to the part of the jaws106,107that must interact with the piece P to be handled. This way, the gripper100can be better utilized.

Secondarily, the gripper100is symmetrical due to the absence of the sensor112between the distal ends106″ or107″ of the jaws106,107, since the jaws106and107are symmetrical and move in mirror-like manner with respect to the longitudinal axis of the gripper100along which the piece is maintained during handling.

Another advantage is that the sensor112can be made with cheap components: in fact, the sensor112is not required to be of the low hysteresis or analog type because the operation of the sensor112is also based on the presence of the elastic element121. In more detail, the spring modulus121is selected so that the spring121can be pressed only if the gripper100grips the piece P; if the gripper100does not pick up the piece, due to an error, the spring121is not compressed.

The closing movement of the jaws106,107on a piece will be described with reference toFIGS.2,2A,3and4A-4C, considering the case in which the gripper100has to pick up three pieces with circular section, but with different diameter, P′, P″ and P′″, respectively.

For example, at first, when the command of picking up the piece P reaches the gripper100, the jaws106,107thereof may be open, as shown inFIG.2, or the jaws106,107may be closed, as shown inFIG.3.

It should be noted that during the closing movement of the jaws106,107, from the position shown inFIG.2, as long as the jaws do not close on the piece P, the angle between the second portion118and the first portion113of the sensor112is maximum, and the magnetic element120is in the position furthest from the electronic circuit116.

In other words, during the closing movement of the jaws106,107, as long as the jaws do not both comes in abutment onto the piece P to be handled, the second portion118of the sensor112, i.e. the sliding block, moves fixedly with the jaw106, i.e. these elements do not pivot with respect to each other on the pin119.

This behavior is due to the fact that the second portion118of the sensor112cannot be rotated on the pin119with respect to jaw106by the wedge-shaped portion110of the piston103as long as the preload of elastic element121is not exceeded; this exceeding condition only occurs when the jaws106,107move to grip a piece P and the wedge-shaped portion110of the piston103moves further in the direction corresponding to spreading out the portions106′ and107′ of the jaws106and107.

This way, i.e. by preventing the relative rotations of the second portion118of the sensor112with respect to the jaw106before the jaws106and107clamp the piece P, the magnetic element120is kept away from the sensor112.

This circumstance is favorable, because although cheap sensors112are adopted, not necessarily of low-hysteresis type, false positive signals are avoided.

FIG.2Ashows the gripper100at a time when the jaws106,107are moving to be closed on a piece P (pieces P of three different diameters are schematically shown): during the closing movement the angle between the second portion118and the first portion113of the sensor112remains constant, and preferably equal to the maximum value, up to the point where the jaws close on the piece P and, after that, said angle decreases as long as the second portion118of the sensor112rotates and reaches the limit stop corresponding to the magnet120in abutment right against the sensor112and corresponding to a null angle.

FIGS.4A-4Cshow the gripper100with the jaws106,107(especially the portions106″ and107″) closed on a small-diameter piece P′, an intermediate-diameter piece P″ and a large-diameter piece P′″, respectively.

As can be seen, in all three cases between the second portion118and the first portion113of the sensor112there is a null angle: the magnet120is in abutment against the sensor and the signal that the piece has been gripped, i.e. the signal indicating that the piece P′, P″, P′″ is closed between the jaws106,107, is generated.

Thanks to the fact that, at first, the jaw106and the second portion118of the sensor112move fixedly and then they rotate with respect to each other, a signal always correct without false positives regardless of the diameter of the piece P′, P″, P′″ can be obtained by the sensor112.

FIGS.6-9show a second embodiment200of the gripper according to the present invention, equivalent to the first embodiment100. Also in this structural variation, two jaws206and207swing on respective pins208,209with respect to the body201, in response to the stresses exerted by an air piston203functioning as an actuator and moving, alternately in the longitudinal direction, inside a cylinder202obtained in the body201.

An elastic element211, basically a preloaded spring, is interposed between the two jaws206,207, on the opposite side of the piston203with respect to the pins208,209, to bring the jaws206,207to the open position when the piston203moves back in the cylinder202. In other words, the spring211exerts a thrust on the distal ends206″ and207″ of the jaws206,207to spread them out, and the piston203exerts a thrust on the shoulders206′ and207′ of the jaws206,207′, by means of a wedge-shaped portion210that slips right between the shoulders206′ and207′ to spread them out, countering the force exerted by the spring211.

The sensor212comprises a first portion213that can be fixed to the shoulder206′ of the jaw206, and a second portion218hinged to the first portion213by means of a pin219. An elastic element221, preferably a spring, is interposed between the two portions213and218of the sensor212. A magnetic element220, that can be seen inFIG.9, is inserted in the second portion218of the sensor; an electronic circuit216detecting the magnetic element220is fitted to the first portion213of the sensor212.

The second portion218has a rounded portion intended to interact with the wedge-shaped portion210of the piston203, like a sliding block. The reciprocating movement of the piston203limits the rotation of the second portion218of the sensor212with respect to the first portion213.

When the jaws206,207are in the closed position shown inFIG.7, the wedge-shaped portion210of the piston203stops against the limit stop222. On the other hand, in the gripping position of the piece P shown inFIG.8, the wedge-shaped portion210of the piston203does not touch the limit stop222.

InFIG.6the gripper200is shown with the jaws206and207open due to the thrust exerted by the spring211. InFIG.7the gripper200is shown with the jaws206and207closed due to the thrust exerted by the piston203. InFIG.8, the gripper200is shown with the jaws206and207in the gripping position of the piece P, i.e. with a piece P held by the distal ends206″ and207″.

The operation of the gripper200is similar to the operation of the gripper100described above.

FIG.10is a perspective and exploded view of the jaw206and the sensor212of the gripper200. As can be seen, the first portion213of the sensor212is provided with a slot213′ in which the electronic circuit216(not shown for simplicity inFIG.10) is slidingly inserted, with the final position of the electronic circuit216that can be adjusted and locked. The first portion213is perforated to allow the insertion of the pin219along an axis parallel to the pins208and209. The shoulder206′ of the jaw206is shaped like a fork and is also perforated with opposing holes215, and elastic protrusions214provided on the sides of the first portion213of the sensor212snap into these holes. A hole218′ is obtained through the second portion218of the sensor212, to house the pin219and allow the hinge coupling with the first portion213to be achieved. Two seats226and223to house the spring221and the magnetic element220, respectively, are provided on the second portion218. Suitable countercheck surfaces224prevent the first portion213from rotating with respect to the shoulder206′ of the jaw206when the sensor212is correctly fitted thereto. The reference numeral225denotes the rounded portion of the sensor212, and in particular of the second portion218intended to move on the wedge-shaped portion210of the piston213, like a sliding block, so that the second portion218is allowed to relatively rotate with respect to the first portion213in response to the stresses exerted by the jaw206when the piece P is gripped.

The space between the jaws206,207remains completely free also in this second embodiment200: the sensor212is not fitted to a distal end206″ or207″ of the jaws206,207, i.e. it is not fitted to the part of the jaws206,207that must interact with the piece P to be handled.

The sensor212can also be made with cheap components, because the low hysteresis type is not required. The spring modulus221is selected so that the spring221can only be pressed if the gripper200grips the piece P; if the piece P is not picked up by the gripper200, due to an error, the spring221is not compressed and this circumstance is distinguished by the sensor212.

FIGS.11-15show a third embodiment300of the gripper. It is a pneumatic gripper300, i.e. whose actuator is a piston303that moves inside a cylinder302defined in the body301of the gripper300, along a direction defined longitudinal. Unlike the grippers100and200described above, in the gripper300the jaws306and307do not rotate but translate closer to and away from each other. In other words, the grippers100and200are angular grippers, and the gripper300is a gripper with parallel jaws306,307.

The jaws306,307can slide on a dedicated guide301′ fixed with the body301of the gripper300. The guide301′ is oriented orthogonally to the longitudinal direction of displacement of the piston303: the displacement of the piston303to the respective closure dead point causes the jaws306,307to move closer to each other and vice versa, the movement of the piston303away from the closure dead point causes the jaws306,307to move away from each other, due to the force exerted by the elastic element311.

The jaws306,307are moved on the guide301′ by respective swinging arms330,331pivoted to the body301of the gripper300at the pins308and309. In particular, the swinging arms330and331each comprise a lobed portion332,333which fits into the corresponding jaw306,307to exert the thrusts in the two translation directions.

In this embodiment300the distal ends306″,307″ of the jaws306,307are identified in the sliding blocks on the guide301′ shown in the figures, and the proximal ends306″,307″ are identified in the swinging arms330and331, which for the purposes of the present invention can be considered as parts of the jaws306,307even if they are not made in one piece with them.

FIG.11shows the gripper300in elevation and perspective, with the jaws306,307open. The figure shows the spring311countering the piston303and the guide301′ as well as the sensor312functionally interposed between the piston303and the proximal end306″ of the jaw306.FIG.12shows the gripper300in elevation and perspective, and partially in phantom view; the piston303is in the respective opening dead point (opposite the closure dead point) and therefore it does not exert a thrust on the swinging arms330,331with its wedge-shaped portion310, so that the spring311keeps the oscillating arms330,331spread out, and therefore keeps the jaws306,307open.FIG.13is an elevation and (longitudinal) sectional view of the gripper300in the configuration with the jaws306,307completely closed; the piston303is in the respective closure dead point, in abutment against the limit stop322, and its wedge-shaped portion310is inserted between the swinging arms330,331so as to spread them out in the area between the same piston303and the pins308,309. In this configuration the lobed portions332,333of the swinging arms330,331are at the minimum distance from each other.FIG.14is an elevation and sectional (longitudinal) view of the gripper300in the configuration with the jaws306,307in the gripping position of the piece P, i.e. in abutment against a piece P to be handled, from opposite parts with respect to the latter.

Considering that the first portion313of the sensor312is fixed to the swinging arm330, which also defines the proximal end306′ of the jaw306, the operation of the gripper300is as follows. When the piston moves towards the respective closure dead point, it counters the second portion318of the sensor312thus limiting the rotation thereof on the pin319with respect to the first portion313, which remains stationary with respect to the swinging arm330. The electronic circuit316inserted in the first portion313and fixed thereto generates an electrical signal indicating the position of the magnetic element320with respect to the electronic circuit316itself. The spring321acts to return the second portion318to its initial position when the gripper300is deactivated, i.e. when compressed air is no longer supplied to the piston303. Similarly, the spring311reopens the jaws306,307when the piston303returns to the opening dead point.

As already noted for the grippers100and200, also in the gripper300the spring321between the two portions313,318of the sensor312contributes to make the system effective. In fact by comparingFIGS.13and14it is possible to deduce that in the condition of closed jaws306,307the spring321is not compressed or is only slightly compressed, while in the condition where the jaws306,307are gripping the piece P, the spring321is compressed. As explained above, the spring321cooperates with the electronic circuit316and the magnetic element320to allow the sensor312to detect without error the case where the piece P is not present between the jaws306,307. In fact, thanks to the described configuration, the spring321is compressed only in the case shown inFIG.14where the jaws306,307actually take the piece P, otherwise the spring321remains uncompressed or only partially compressed. The reason is that the jaw306is rotated with respect to the closed position when a piece P is held. As a result, by appropriately selecting the spring modulus321, for example by carrying out tests, the sensor312can be manufactured without using low-hysteresis components.

Also, the gripper300is self-centering, like the grippers100and200described above.FIG.14shows that the piece P is held along the longitudinal axis of the gripper300.

FIGS.16-20show a fourth embodiment400of the gripper. It is an angular gripper with pneumatic actuator440orthogonal to the longitudinal axis along which the piece P is kept. In particular,FIGS.16-18show the gripper400in elevation and longitudinal section, with the jaws406,407open, closed, and gripping the piece P, respectively.FIG.19shows gripper400in elevation and perspective, with the jaws406,407open.FIG.20is an exploded view of the gripper400.

In more detail, the jaws406,407are fitted to the body401of the gripper400so as to be pivotable of the pins408,409, i.e. they can swing. Compressed air is supplied into the body401via the nozzle405. Inside the body401there is a volume440connected to the nozzle405and partitioned in two opposing chambers441and442that are arranged on opposite sides with respect to the nozzle405and in which respective air pistons403′ and403″ are movable. The compressed air injected through the nozzle405causes the pistons403′ and403″ to move away from each other in the respective chambers441and442; the pistons403′ and403″ can slide in the respective chambers441and442and are constrained to each other by a telescopic coupling. In particular, the piston403″ has a shaft partially inserted in the piston403′ in a sliding way.

The piston403′ acts on the shoulder406′ of the jaw406, and the piston403′ acts on the shoulder407′ of the jaw407, so that when the gripper is activated by supplying compressed air, the pistons403′,403″ move away from each other and spread out the shoulders406′,407′ of the jaws406,407, causing them to rotate on the pins408,409and causing the distal ends406″ and407″ of the same jaws406,407to move closer to each other. As mentioned above, the pistons403′,403″ move along a direction orthogonal to the longitudinal axis of the gripper400.

When the gripper400is deactivated, an elastic element411, practically a spring, returns the jaws406,407to the open position shown inFIGS.16and19. The spring411is housed in a special seat in the body401of the gripper400, oriented parallel to the movement direction of the pistons403′,403″, but obviously arranged opposite them with respect to the pins408,409.

The gripper400is equipped with a sensor412fitted on board the jaw407, and in particular arranged on the shoulder407′. InFIG.20the sensor41has been omitted for simplicity, but is clearly visible inFIGS.16-19.

The sensor412comprises a first portion413made in one piece with the shoulder407′ of the jaw407, in which there is an electronic circuit416equipped with a LED light indicator450. The magnetic element420of the sensor412is housed on board the piston403″, in a corresponding seat, and a spring421is functionally interposed between the piston403″ and the shoulder407″ of the jaw407. The spring421is held on the piston403″ by the shoulder407′ of the jaw407, which prevents the spring421from accidentally coming out.

The operation of the sensor412is as follows. In the initial condition of inactive gripper400, shown inFIG.16with the jaws406,407open, the spring421is not compressed, or is only slightly compressed, and the magnetic element420is at a first distance from the electronic circuit416. When the gripper400is activated, i.e. compressed air is supplied thereto, the pistons403′ and403″ forces the jaws406,407to the closed position shown inFIG.17: since the pistons403′ and403″ reach a limit stop on the elastic rings436and437, the movement of the pistons403′,403″ away from each other does not cause the spring421to be compressed.

In other words, the elastic rings436and437stop the pistons403′ and403″, preventing the magnetic element420from stressing the electronic circuit416if the gripper400closes uselessly, i.e. if the piece P is not picked up and held between the jaws406,407.

When the gripper400picks up a piece P, as shown inFIG.18, the compression of the spring421compensates for the size of the piece P: in this position the shoulder407′ of the gripper407″ is closer to the piston403″ with respect to the position shown inFIG.17and, therefore, the magnetic element420is closer to the electronic circuit416, the latter detecting the former and turning on the LED450to confirm that the piece P has been gripped. The components are caused to return to the initial position ofFIG.16by the deactivation of the gripper400.

Therefore, even in the gripper400the spring421of the sensor412is compressed only when the piece P is picked up, while in all other positions of the jaws406,407there is no substantial compression of the spring421. The spring421cooperates with the electronic circuit416and the magnetic element420to distinguish in effective, error-free and simple way, the gripping condition of the piece P.

Even in the gripper400the space around the jaws406,407remains fully usable since it is not encumbered by the sensor412. Even for the clamp400, the sensor412does not need to be expensive.

Based on the provided examples, it can be considered the following method for detecting the presence of a piece between the jaws of an industrial manipulator gripper. The method is based on the fact that between the distal ends of the jaws there is not a magnetic sensor112,212,312,412, as provided in traditional solutions, but there is precisely the piece P to be handled, even if in a different position, functionally interposed between the actuator of the gripper and the proximal ends, or shoulders, of the jaws.

The sensor112,212,312,412is made with a magnetic element120,220,320,420movable with respect to a corresponding electronic detecting circuit116,216,316,416univocally depending on the relative position of the jaws106-107,206-207,306-307,406-407, and with an elastic element121,221,321,421that counteracts the approach of the magnetic element120,220,320,420with respect to the electronic circuit116,216,316,416. By correctly selecting the elastic element, i.e. selecting the correct force it exerts, the gripper is configured so that the elastic element121,221,321,421is subject to compression only when the gripper100,200,300,400actually holds a piece P.

This method has two main advantages:with respect to the traditional solution in which the magnetic element is positioned on the piston and therefore the sensor must be of the analogical or low hysteresis type, the method according to the present invention can also be implemented with cheaper digital ON-OFF sensors, because the elastic element121,221,321,421guarantees the correct operation, i.e. it guarantees that the sensor112,212,312,412generates a gripping signal of the piece P only when the piece P is actually between the jaws106-107,206-207,306-307,406-407of the gripper;compared to the traditional solution in which the magnetic element is positioned on a gripper jaw, the method according to the present invention can be implemented by positioning the sensor112,212,312,412in contact with the actuator, in a less bulky position.

FIGS.1-20show examples of grippers100,200,300,400with two jaws, but in general the present invention is also applicable to grippers with only one jaw, or with more than one jaw, for example grippers with three radial jaws.

FIGS.1-20show examples of grippers100,200,300,400with pneumatic actuator, but in general the present invention is also applicable to grippers with hydraulic or electric actuator.

FIGS.21-25show a fifth embodiment500of the gripper according to the present invention, for which the applicant reserves to file a divisional patent application. It is also in this case an angular gripper500, in which two jaws506and507swing on respective pins508,509with respect to the body501, in response to the stresses exerted by an air piston503which operates as an actuator and moves, alternately in the longitudinal direction, inside a cylinder502obtained in the body501.

An elastic element511, basically a preloaded spring, is interposed between the two jaws506,507, on the opposite side of the piston503with respect to the pins508,509, to bring the jaws506,507to the open position when the piston503moves back in the cylinder502. In other words, the spring511exerts a thrust on the distal ends506″ and507″ of the jaws506,507to spread them out, and the piston503exerts a thrust on the shoulders506′ and507′ of the jaws506,507′, by means of a wedge-shaped portion510that slips right between the shoulders506′ and507′ to spread them out, countering the force exerted by the spring511.

The gripper500comprises a pneumatic-type sensor512. The sensor512comprises in turn a first portion513that can be fixed to the shoulder506′ of the jaw506, and a second portion518hinged to the first portion513by means of a pin519. An elastic element521, preferably a spring, is interposed between the two portions513and518of the sensor512.

A duct513′ is defined in the first portion513and can be connected by means of a nozzle to an outer vacuum source, e.g. an extractor, or a vacuum pump, so that a depression, or vacuum, can be created in the duct513′.

A shutter520, preferably spherical as shown in figures, for example made of rubber, is inserted in the second portion518of the sensor512; unlike the solutions described above, which are equipped with an electronic circuit for detecting a magnetic element, in the pneumatic sensor512the detection of a magnetic element by Hall effect is not provided, being instead provided the detection of the pressure value (of depression in particular) in the duct513, as will be described later on.

The second portion518has a rounded portion intended to interact with the wedge-shaped portion510of the piston503, like a sliding block. The reciprocating movement of the piston503causes the second portion518of the sensor512to rotate with respect to the first portion513and, therefore, causes the shutter520to be displaced with respect to the first portion513and, therefore, with respect to the duct513′.

When the jaws506,507are in the closed position shown inFIG.23, the wedge-shaped portion510of the piston503stops against the limit stop522. On the other hand, in the gripping position of the piece P shown inFIG.24, the wedge-shaped portion510of the piston503does not touch the limit stop522.

InFIGS.21and22the gripper500is shown with the jaws506and507open due to the thrust exerted by the spring511. InFIG.23the gripper500is shown with the jaws506and507closed due to the thrust exerted by the piston503. InFIG.24, the gripper500is shown with the jaws506and507in the gripping position of the piece P, i.e. with a piece P held by the distal ends506″ and507″.

FIG.25is an exploded perspective view of the gripper500. As can be seen, the first portion513is perforated to allow the pin519to be inserted along an axis parallel to the pins508and529. The proximal portion, or shoulder506′ of the jaw506, is shaped like a fork and is also perforated with opposing holes515, and elastic protrusions514provided on the sides of the first portion513of the sensor512snap into these holes. A hole518′ is obtained through the second portion518of the sensor512, to house the pin519and allow the hinge coupling with the first portion513to be achieved. Two seats, to house the spring521and the shutter220, respectively, are provided on the second portion518. Suitable countercheck surfaces524prevent the first portion513from rotating with respect to the shoulder506′ of the jaw506when the sensor512is correctly fitted thereto. The reference numeral525denotes the rounded portion of the sensor512, and in particular of the second portion518intended to move on the wedge-shaped portion510of the piston513, like a sliding block, so that the second portion518is rotated relatively with respect to the first portion513.

Referring in particular toFIGS.23and24, when the gripper500is activated, i.e. when the piston503forces the jaws506,507to close, two circumstances may occur:in a first case the gripper500does not pick up the piece P, as inFIG.23. An angle is defined between the first portion513and the second portion518of the sensor512and the shutter520does not close the duct513′. A special outer instrument designed to detect the depression in the duct513′ detects a first value, for example corresponding to −0.3 bar;in a second case, the gripper picks up and holds a piece P between the jaws506and507. The second portion518of the sensor512is in abutment against the first portion513, due to the thrust exerted by the jaw506, and the shutter520closes the duct513′. The outer instrument detects a second depression value in the duct513′, for example corresponding to −0.8 bar.

Therefore, the operation of the sensor512is simple and based on the detection of the pressure (depression) value in the duct513′: the variation of the measured value distinguishes the case in which the gripper500has correctly picked up a piece P from the case in which the gripper500has been activated uselessly, without picking up the piece P.

The space around the jaws506,507remains completely free even in this fifth embodiment500: the sensor512is not fitted to a distal end506″ or507″ of the jaws506,507, i.e. it is not fitted to the part of the jaws506,507that must interact with the piece P to be handled.

The sensor512can also be made with cheap components easily available on the market and, in addition, has the advantage that the reading of the pressure value in the duct513′ can be done by outside means connected to the sensor512, even remotely positioned and very accurate, that are not susceptible to displacements and stresses precisely because not fitted on board the gripper500.