Gripping Device with Holding Jaws or Holding
Fingers for the Handling of Rod or Bar Shaped Articles.
The invention relates to a gripping device with gripping jaws or gripping fingers for the handling of rod or bar shaped articles, such as reinforcement steel, said gripping device being arranged at the end of a robot arm. It is the purpose of the invention to provide a gripping device which, within certain limits and under a controlled resistance, is able to follow violent and sudden movements of one or more rod shaped articles being processed, e.g. being cut. Thereby is avoided the relatively extensive power effects influencing a robot arm, if a gripping device is secured in a fixed position and should obstruct the movement of an article. As an example of an article being moved due to the processing and during the processing can be mentioned reinforcement steel which by means of a scissor tool should be cut free from a rod of reinforcement steel . Here the rod will be bent around the cutting edge of the scissor tool, if the part of the rod situated on one side of the scissor tool is secured in its position and thereby is prevented fro moving. According to the invention this purpose is achieved by a gripping device of the kind mentioned above, and which is characterized in that the gripping device with its gripping jaws is arranged so that it is pivotable around a jaw axis being parallel with the longitudinal direction of the grippinr fingers, that the device is pivotable in relation to tne robot arm around a hinge axis being parallel with the jaw axis, that it is movably arranged between a fixed position and the hinge axis, and that the gripping device is so connected to a servo control means, such as a pneumatic cylinder, that this may bias the gripping device with a pressure in the direction away from the hinge axis and towards the fixed position.
Thereby is achieved that the gripping device in a resilient way, e.g. resilient in a pneumatic way, without substantial resistance may yield under the influence of limited, forced movements deriving from an article gripped by the jaws, namely a rotation around the hinge axis, a rotation
around the jaw axis and a movement towards the hinge axis. This makes the gripping device suitable for gripping firmly around an article, e.g. a reinforcement steel, before it - e.g. after a bending operation - shall be cut free from a rod of reinforcement steel, lock the grip and follow the deflec¬ tion of the reinforcement steel during the cut and then carry the reinforcement steel away for packing. Seeing that the gripping device thus may yield for forced movements, it is avoided that the robot should be dimensioned to produce the relatively large forces necessary for securing the gripping device in a fixed position and thus prevent a deflection of the reinforcement steel during the cut.
An embodiment of a gripping device according to the invention can be characterized in that the gripping device with the gripping jaws is arranged on a swivel plate imot. tje swivel plate of which is pivotably connected via a swivel plate housing to a slide block which can be displaced on a slide bar, and which has a side adapted for abutting against a face on a stop plate, that the swivel plate is pivotable in relation to the swivel plate housing on the slide block around the jaw axis being parallel to the longitudinal direction of the gripping fingers, thar. the slide bar is arranged on a plate being hinged to a robot arm plate which in turn is secured to the robot arm, said plates being pivotable in relation to each other around the hinge axis being parallel to the jaw axis, that the slide block extends from the stop plate towards the hinge axis, and that a servo control device, such as a pneumatic cylinder, in its one end is hinged to the robot arm plate and in its other end to a face of the swivel plate housing turning towards the hinge axis.
The invention will now be described in more detail in connection with a preferred embodiment and with reference to the drawing in which Fig. l shows a perspective view of an embodiment of a gripping device according to the invention, where the gripping device is arranged pivotably around an axis C,
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Fig. 2 shows a section of a swivel plate, a plate for reception of a hinge for a piston rod from a pneumatic cylinder and damping springs inserted between the two plates, and Fig. 3 the jaws of the gripping device of Fig. 1 in a working position pivoted 90° around the axis M.
The gripping device D is preferably used in connection with the cutting of ready-bent pieces of reinfor¬ cement stee] from one or two rods of reinforcement steel and an immediately subsequent handling of the cut piece/s of reinforcement steel. Although two rods are bent, cut and handled, the following explanation will only deal with one rod or one piece.
In that case a rod of reinforcement steel to be bent is taken along a conveying path towards and past a scissor tool with cutting edges, and further on to a rod bending apparatus in which a piece of the rod is bent successively. Then the holding jaws A of the gripping device D is moved into a position around the ready-bent rod or piece of rod on a predetermined gripping place thereon, e.g. iπt ediately after the intended cutting location of the scissor tool, and then the jaws is closed around the rod piece for securing it in the gripping device D.
The cutting edge of the scissor tool has a cutting direction which in Fig. 1 is parallel to the moving direction of the gripping jaws A when the gripping device D is in its fixed position abutting against a stop plate F. The lower cutting edge can be firmly arranged and the upper cutting edge can be movable, and the piece of the reinforcement steel to be cut off extends towards that side where the movable cutting edge is located, i.e. after the scissor tool.
During the cutting that part of the rod lying on the conveyor upstream of the scissor tool, cannot move sub¬ stantially in a direction perpendicularly to the cutting edge of the scissor tool. Consequently, it is the freely extending bent end of the rod after the scissor tool that has to move, due to the effect of the forces exerted by the cutting edge
of the scissor tool on the rod during the cutting.
Said forces may cause the freely extending end of the rod to deflect downwards during the cutting, e.g. 30°in relation to the part of the rod lying on the conveyor. Said deflection is happening almost momentarily, and while the freely extending, possibly ready-bent end of the rod is cut free.
If a robot arm with gripping jaws A, gripping firmly around a reinforcement steel during the cutting off thereof in order to handle it immediately after the cutting, also during the cutting off has to prevent the rod of reinforcement steel to be deflected or bent, the gripping jaws would have tc absorb relatively large forces being transferred to the parts of the robot, which therefore should be dimensioned to absorb said large forces.
By the embodiment shown in Fig. 1 a rod of reinfor¬ cement steel can be caken forward and between the jaws A on the gripping device D, and the freely extending, possibly ready-bent end of the reinforcement steel to be cut off, can be taken forward at the outer side of the stop plate F.
A scissor tool is arranged on the side of the gripping device D turing away from the freely extending end of the rod. The scissor tool may have a stationary, lower cutting edge and an upper cutting edge movable parallelly with the jaws A, said upper cutting edge being arranged between the lower cutting edge and the gripping device D. In that case the freely extending end of the rod will during a cutting operation deflect anticlockwise around the lower cutting edge of the scissor tool. As shown on the drawing the gripping device is secured to a swivel plate being supported pivotably around the axis M in a swivel plate housing which along with the swivel plate forms a swivel plate unit E.
The swivel plate unit E is secured to a slide block K being movable along a slide bar G being secured to a plate H, which in its one end is supported pivotably around the axis C and at its other end carries a stop plate F. The pivoting of the plate H is limited by two adjustable stops on
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a robot arm plate J which pivotably supports the plate H around the hinge axis C. A pneumatic cylinder B is at its one end pivotably connected at Q with the swivel plate housing in the swivel plate unit E and at its other end it is pivotably connected with a bracket R on the robot arm plate J.
Before the cutting the jaws A of the gripping device D are arranged in a firm engagement with the rod part to be cut, and the swivel plate in the swivel plate unit E is forced against the stop plate F by a pressure in the pneuma- tic cylinder B.
If the lower, fixed cutting edge of the scissor tool is aligned with the hinge axis C, the jaws A will during a cutting movement make a circular movement around the hinge axis C. The movement is counteracted by a pressure in the pneumatic cylinder B which acts as an air spring. The pressure in the pneumatic cylinder B may have a size which is sufficient to take the gripping device D and the cut off rod part secured therein back to its starting position before the cutting. Then the robot arm can take the cut off and possibly redy-bent rod part away to a bundling of rod parts.
The gripping device D is normally arranged so closely to the cutting edge of the scissor tool as psosible in order to obtain the smallest possible pivoting of the gripping device D during the cutting. During the cut the parr of the rod secured by the jaws A will make a circular movement having its centre in the cutting edge of the scissor tool. This means that it is insufficient that the gripping device D is pivoting around the hinge axis C. The gripping device D iε in addition thereto forced to pivot anticlockwise around the jaw axis M and make a parallel displacement towards the hinge axis C.
Said parallel displacement is made possibly by the gripping device D being secured to the swivel plate in the swivel plate unit E, which is secured to a slide block K, and which will follow the pivoting of the gripping means D around the jaw axis M. Thus, a corner on the side of the swivel plate turned towards the inner side of the stop plate F, will r
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press against the stop plate F and during the pivoting will press the swivel plate E and the slide block K connected thereto along the slide bar G against the hinge axis C.
During the cutting operation the jaws A may follow that part of the rod being cut, apart from the resistance exerted on the swivel plate E in the direction against the stop plate F by a pressure from the pneumatic cylinder B. Said pressure can preferably be so high, that the gripping device D, which with its jaws A grips the cut off rod part, after the cut is pressed backwards to its starting position, wherein the plate K is pivoted to abut its one stop and the swivel plate is pressed to abut the stop plate F.
Fig. 2 shows the pivotable swivel plate, a plate L on the housing for adopting a hinge Q for a piston rod on the pneumatic cylinder B, and damping springs P inserted between said two plates. Said springs P may have such characteristic and such location that they define a resting position for the unloaded gripping means D around the jaw axis M, while the pressure in the pneumatic cylinder B only serves to take the gripping device back to its starting position with the plate H abutting one of its limit stops and with the swivel plate in the swivel plate unit E abutting the stop plate F after a cutting.
The gripping device D shown in Fig. 3 is pivoted 90° in relation to the gripping device of Fig. 1, so that the rod to be gripped after bending and before cutting, can be gripped at a location where the rod extends perpendicularly to the direction of that rod being gripped by the jaws A in Fig. 1.
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