Tool holder

Device at tool holder (10) of the kind comprising an essentially C-shaped frame preferably having a long inner range, which frame at its free shank ends carries said tool, for instance a riveting, a glueing or a welding unit. The holder (10) comprises a truss or frame work, which includes an outer and an inner C-shaped frame (11, 23) and a number of slewing brackets (27–32) connected to these. The frames (11, 23) and the slewing brackets (27–32) are arranged to form a number of connected triangular sections, which connection points (18–22, 37) are designed as intersections or joints. The outer C-shaped frame (11) is arranged only to support thrust forces and the inner frame (23) thrust and tensile forces and the slewing brackets (27–32) substantially tensile forces.

The present invention relates to a device in tool holders and of the kind which comprises a C-shaped frame, has a preferably long inner range, which frame at its free shank ends carries said tool, for example a riveting, a glueing or a welding unit.

THE BACKGROUND OF THE INVENTION AND THE PROBLEM

C-shaped frames of the above mentioned kind are previously known and are used for joining of for instance car body components, frame works, train cars, air crafts, etc. They are made as I-shaped section in high tensile steel since high requirements are put on the stiffness and the structural strength of the frame. Particularly when working operations, such as e.g. riveting, is in question, large opening forces arise on the shanks of the C-shaped frame. The frame is also to be exposed to a large number of working cycles and a minimum of 2 millions cycles is a demand. The C-frame must be able to operate on deeply situated parts in certain situations, i.e, be able to reach a working area which is situated e.g. 1 meter inside an outer limitation. At large scale production in the automotive industry the C-shaped tool holder is being handled by a robot, which means that the weight of the C-frame should be so low that the total weight of the system is less than the allowed operation weight of the robot. At manual operation it is also desired to minimize the mass of the system.

Using the robots of today, one has reached and in some cases also exceeded the weight limit, but the market demands both larger and more stable tool holders with maintained or even lowered weight. The investments in robots are so high that it must be possible to use existing ones even for new and more extensive working operations.

Tests have been made to produce C-shaped frames from composite materials as solid models but the load strains in the intersections in the form, i.a., of shear and tear stresses in the glue joints will become so high, that these tests could not be performed. A typical steel C-frame, having an inner depth of 850 mm, a gap between the ends of the shanks of 400 mm and a calculated load in the form of opposed directed forces of 53 kN, has a weight of about 150 kg at a maximal permitted deflection of 7 mm between the ends of the shanks. This weight together with the weight of the necessary tool equipment exceed the carrying and operating capability of the robot and are therefore not acceptable.

THE OBJECT OF THE INVENTION AND THE SOLUTION OF THE PROBLEM

The object of the invention is to provide a tool holder, which:a. has a low weight,b. has a high stiffness,c. has a high strength,d. has a simple construction,e. is price-worthy,f. can easily be varied in shape and form,g. can operate in difficult environments, e.g., welding sputters,h. has a long service life and high reliability.

These tasks have been solved by the features defined in the claims.

DESCRIPTION OF AN EMBODIMENT

The tool holder according to the invention consists of an outer C-shaped frame11, which in turn includes six frame beams12–17, of which beams12,13and17,16form the shanks of the C and the beams14and15the intermediate part between the shanks. Beams12–17are interconnected end-to-end via intersections18–22, so that they together form a C.

Inside the outer C-shaped frame11, is provided a second C-shaped inner frame23, comprising the frame beams24and25, which also form the shanks of the inner frame23, while its intermediate part between the shanks consists of beam part26.

The outer and the inner C-frame11,23are interconnected partly via slewing brackets27to32and at the end of the shanks via unit attachments33and34. The intersections18–22are designed with connecting ears35having a through bore36for shaft journal, which form articulated joints37for the slewing brackets27–32. In the same way the inner connections between the slewing brackets and the inner frame23are designed as joints37. The beam part26and the slewing brackets29,30are designed as a fixed triangular construction part38, at which is provided a holder attachment39e.g. for a robot arm (not shown).

The intersections18–22and the unit attachments33,34are designed with guide flanges40and thrust areas41for guidance of and pressure transfer to the end part and end areas42respectively of frame beams12–17. By angularly adjustment the thrust areas41of the intersections, the ends of the frame beams can be cut perpendicularly, which simplifies manufacturing.

The torsional rigidity in the C-shaped frame is suitably obtained by the attachment of stiffening plates43at both its flat sides, which suitably are connected to the frame beams12–17and24,25during load subjected to the frame. The connection can be a glue joint, riveted joint or screw joint or the like. The material can be steel, aluminium, fibre reinforced plastic plates or equal.

In early construction work it proved itself that a frame work construction with intersections free from moments for weight reasons was preferred above a construction having moment absorbing intersections. Solutions comprising moment supporting intersections must be made relatively heavy and unwieldy to be able to handle the heavy loads. The key to achieving a light and durable construction showed to be designing the geometry of the frame work thus that all incoming bars to an intersection meet at one common point. The selected geometry resulted in that the C-frame11is put together by a number of interconnected triangles, where at least one side of a triangle is shared with the adjacent triangle.

Since the specific stiffness for composite materials exceeds the one for steel, it is desirable to use as high a ratio of composite material as possible to minimize the weight for the selected stiffness. The chosen construction principle with essentially moment-free intersection results in the outer frame being subjected to only one-axis loads; i.e., compressing strains, whereby composite material is especially suitable. As composite material can be used different kinds of reinforced plastic e.g., carbon fiber reinforced plastic, having a coefficient of elasticity of about 95 in longitudinal direction compared to about 25 for steel, which means that the carbon fiber frame is almost four times lighter than the corresponding steel frame. Since also combined loads arise in the inner parts of the outer frame and steel is a more cost effective construction material, these parts may suitably be of steel or a combination of steel and carbon fiber reinforced plastic, which in the described embodiment has been selected for the frame beams24and25, where the inner part of the frame beam is a carbon fiber beam44and the outer parts are steel rods. The weight of the whole tool holder is about half the weight of a steel frame having corresponding performance.

However, this does not exclude, that selected parts of the construction can be replaced of composite material, in case the requirements of lowering the weight and/or stiffness and strength are further increased even more.

In order to optimize the properties of the material the fibres are oriented in the extension of the beams, i.e., longitudinally, which means that the beams can be sawed from carbon reinforced plastic plates and be cut into suitable lengths, whereby the costs for the most expensive parts in the construction can be kept low. The selected construction principle does not require special moulding tools, but permits shell-moulding and modification without large initial costs.

The modified embodiment shown inFIGS. 6 and 7differs from the above described in that several joints have been replaced by fixed intersections, but with the maintained requirement, that all connection points are moment-free. By this design it is possible to fixedly connect the slewing brackets27,28,31and32to the frame element38, as to obtain the appearance shown inFIG. 7. The intersections18–22are fixedly integrated to the slewing brackets as to reduce the number of associated parts. The frame element38is suitably made of metal, for example of steel. The inner frame beam is24and25are in the same way as before articulately connected to the frame element38.

A disadvantage of designing all intersection points free of moments, is that the tool holder is so deformed during a load, seeFIG. 8, that the connection surfaces of the unit attachments33,34not remain parallel but will form an angle α with the horizontal plane.

When high requirements are put on the accuracy in the working process, i.e., that both parts of the tool unit45, which can be a riveting unit45aand a riveting knob45b, are essentially in alignment during the riveting operation, or in other words that the connection surfaces of the unit attachments33,34essentially remain parallel, the principle with the moment free intersections or joints can not be established. To be able to control the deformations of the C-shaped tool holder at load, it is suitable that moment is applied into one or more intersections or bars, which is achieved by that the centre line46of the incoming rods to an intersection do not meet in a common intersection point. Therefore all intersections will not be moment free.

InFIG. 9it is shown how to control the deformation, to achieve certain requirements, e.g., the above mentioned parallelism. In the unit attachment33the intersection point47of the centre line46has been moved outside the attachment33, as to induce a moment using the moment arm49when for instance a riveting load, as shown by arrows50, attacks the unit attachments33and34.

Further has moment been applied into the intersections20and21, by displacing the attachment points48,51of the frame beams14,15,16corresponding to the length of the moment arms52and53. Thereby the frame beam16,25and13,24are deformed axially and through bending.FIG. 10gives an example of this, whereby the parallelism of the connection surfaces of the unit attachments33,34can be maintained.

Intersection point101is shown, at which the load line50intersects with the center line46of said first outer shank portion16at an intersection point101located closer to a central portion of the tool holder, along the center line46of said first outer shank portion16, than the intersection point47at which the center line46of the first inner shank portion25and the center line46of the first outer shank portion16intersect.

In this embodiment the stiffening plates43are omitted.

The invention is not limited to the embodiment described and shown, but a number of variations are possible within the scope of the claims. Thus, the holder may consist of a larger or smaller number of triangular sections and different constructions of intersection joints are possible.

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