WO1998037333A1

WO1998037333A1 - Bolt joint

Info

Publication number: WO1998037333A1
Application number: PCT/SE1998/000297
Authority: WO
Inventors: Ove Kullborg
Original assignee: Abb Ab
Priority date: 1997-02-20
Filing date: 1998-02-19
Publication date: 1998-08-27
Also published as: SE9700590L; SE510700C2; SE9700590D0

Abstract

A bolt joint in an industrial robot for fixing a first body (1) to a second body (2). The joint allows a non-play transmission of a torsional force acting between the bodies. An expandable conical first sleeve (8) makes contact with a hole wall of a cylindrical hole (7) common to both bodies. The joint also comprises a conical second sleeve (9) which is adapted to penetrate into the first sleeve (8). A bolt (3) is arranged running coaxially through the sleeves. When the bolt is clamped, the second sleeve (9) penetrates, with force, into the first sleeve (8) and forces the first sleeve (8) to expand. The strong expansion results in the first sleeve (8) deforming deviations in the hole (7), such that it makes butt contact with the common hole wall.

Description

Bolt J oint

TECHNICAL FIELD

The present invention relates to a bolt joint of the kind described in the preamble to claim 1. More particularly, the invention relates to a bolt join which is intended for non- play transmission of a torque between two bodies of an industrial robot.

BACKGROUND ART

A bolt joint usually means a joint in which screws provided with nuts transmit forces between connected objects by bearing stress, shearing and by tensile forces in the screws. The screws may also be threaded direct in the material to either of the connected objects. By bolt or screw is to be understood here an entirely or only partially externally threaded cylindrical body provided with a head.

To transmit shear forces, friction forces between the inter- conected objects in a so-called friction joint are often utilized. By prestressing of the screws, a normal pressure is obtained between opposite surfaces in the joint and the transmission of forces takes place by friction between these surfaces. If a friction joint is loaded such that the fric- tional resistance is exceeded, movement of the joint arises until contact between the screw and the material occurs . The force transmission then occurs by bearing stress and shearing in the screw. However, the friction remains to a certain extent and cooperates .

The movement which arises when the friction force is exceeded is a problem in a plurality of applications . Such a movement is especially unsuitable in joints which are to transmit a torque between two bodies. Practical difficulties arise in determining the prestressing force which must be applied in order not to exceed the friction force. The prestressing force in the screw is often determined by applying a certain torque when tightening the nut. In addition to the direct uncertainty in correctly applying a sufficient normal force, there is also an uncertainty as regards the reduction of the prestressing force because of material changes in environment and time.

To avoid movement or play between the interconnected objects in a friction joint, it is known, in joints with plane surfaces, to apply force-transmitting pins which cross the common dividing surface. The pins are applied in a perpendicularly arranged hole in one of the bodies and penetrate into a corresponding equally oriented hole in the other body. The pin is applied with such precision that a movement without deforming the pins is rendered impossible. This method requires that the holes of the pins of the two objects which are to be connected together are jointly reamed. Reaming implies that the holes, into which the pins are to fit, are machined with a rotating cutting tool to great accuracy. This machining generates chips and is thus unsuitable in connec- tion with, for example, mounting of an industrial robot. A further drawback is that the two jointly reamed objects form pairs and thus cannot be exchanged or replaced without carrying out renewed reaming.

From SE 502 112, an expanding mandrel is previously known. The mandrel comprises a conical outer sleeve provided with slits, which cooperate with a conical nut. By stressing a screw threaded in the nut, the outer sleeve is brought to expand in the radial direction. The known mandrel is not adapted to absorb tensile forces.

SUMMARY OF THE INVENTION

The object of the invention is to produce a bolt joint which fixes two bodies to each other and transmits shear forces, without play, from a torque of one body to the other. The joint is to be safe and should be capable of being rapidly applied in connection with mounting. The method is to eliminate chip-generating machining at the site of mounting and allow the interconnected objects to be easily replaced without any cutting machining occurring at the site of mounting. The method should also allow one body, without machining of the holes, to be fixed to a plurality of different bodies.

A device which fulfils the above-stated object is achieved according to the invention by a bolt joint with the characteristic features described in the characterizing portion of claim 1 and by a method with the characteristic features described in the characterizing portion of claim 5. Advantageous embodiments are indicated by the characteristic features in the characterizing portions of the dependent claims .

According to the invention, there is arranged between two connected bodies, the opposite surfaces of which are substantially plane, at least one transmission member, common to the bodies, for transmitting shear force. This member is adapted to expand in a hole common to the bodies such that complete contact is obtained with the inside of the hole. For the purpose of absorbing tensile forces in a normal plane to the oppositely-arranged surfaces of the bodies, bolts between the bodies are arranged through the mentioned transmission member .

By arranging the transmission member expandable, complete contact between the member and the hole, in which it is placed, is safely obtained. The transmission member comprises an outer conical surface and an inner conical surface, which are placed with their tips opposite to each other in each other. In a preferred embodiment, the outer sleeve is provided with a longitudinal slit, which facilitates the expansion. The slit also has the advantage that the joint can be easily loosened, whereby the outer sleeve resumes its original relaxed shape and allows the connected bodies to be easily separable. The prestressing force is arranged in the normal manner with threaded bolts, which may be screwed into one of the connected bodies or be clamped by means of nuts. In a preferred embodiment, the bolts are placed concentrically with the sleeves, in which case the advantage may be utilized of simultaneously clamping both the friction joint and the expansion force of the sleeves.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in greater detail by description of an embodiment with reference to the accompanying drawing, wherein

Figure 1 shows a section of a bolt joint with a shear force- transmitting member between two connected objects according to the invention,

Figure 2 shows a view of an outer, slitted, conical sleeve comprised in the shear force-transmitting member,

Figure 3 shows a section of an alternative embodiment of the joint, and

Figure 4 shows a section of a preferred embodiment of a screw joint according to the invention, wherein the bolt is threaded direct in one of the connected objects.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 shows a bolt joint which joins a first body 1 to a second body 2. A through bolt 3 is clamped with a nut 4, whereby the bolt and the nut, via a first washer 5 and a second washer 6, achieve a prestressing force across the joint. Across the bodies there is arranged a cylindrical hole 7 with a preferably circular cross section. Concentrically with the bolt 3 , there are arranged in the hole 7 an outer conical sleeve 8 and an inner conical sleeve 9 inserted thereinto. The two sleeves are made of a material which has greater hardness than the two bodies to be joined together. Usually, the sleeves are made of hardened steel. A deformation ring 11 of an elastic material, the hardness of which is adapted to create a desired axial force on the inner sleeve, is placed between the first washer and the inner sleeve.

Since the inner sleeve is pressed, with force, into the outer sleeve, an expansion force is achieved which causes the outer sleeve to be pressed with great force against the inside of the hole 7. Often there are small deviations between the holes, which results in the holes not being exactly concentric . This leads to the creation of a small lug somewhere along the edge of the hole at the transition from one body to the other. Since the outer sleeve is harder than the joined- together bodies, the sleeve deforms such small deviations between the holes, whereby full contact is achieved between the sleeve and the hole.

To facilitate the expansion of the outer sleeve, this is provided with a slit 10 according to Figure 2. According to this embodiment of the invention, the slit is formed with a waveform such that the two edges on both sides of the slit exhibit fingers which overlap each other in the lateral direction. This shape gives a better contact with the inside of the hole and the expanded slit allows deformed material to be more easily removed. However, the invention is not limited to a joint with precisely the shown design of the slit. The slit may thus be formed in a plurality of ways which allow the sleeve to expand.

An advantageous embodiment of the invention is shown in Figure 3. The hole 7 is here not continuous but only partly hollowed out in the second body 2. However, the bolt is continuous and may be threaded in the outer part of the second body or freely continuous and clamped with a nut 4 on the outside. Still another advantageous embodiment of the joint is shown in Figure 4. The first body 1 is here joined to a second larger body 2. The total thickness of the two joined bodies is here larger than the bolt, so no nut can be applied. The embodiment according to Figure 4 shows how a bolt may be clamped and achieve a prestressing force over the bodies by arranging, in the second body, a threaded hole into which the bolt is screwed.

The two conical sleeves are arranged in the last two embodiments in the same way as in Figure 1, with the only difference that they rest against the bottom of the hole.

Although a combination of bolt joint and sleeves in the same hole is advantageous, the sleeves may be placed in a hole, common to the two bodies, in an optional position at the boundary between the joined bodies. The two sleeves may also be brought, in an optional manner, to be pressed into each other such that the outer sleeve expands and, by deformation of deviations in the hole, create a non-play contact between the two bodies .

Claims

1. A bolt joint in an industrial robot for fixing a first body (1) to a second body (2), said joint allowing a non-play transmission of a torsional force acting between the bodies, whereby an expandable conical first sleeve (8) makes contact with a hole wall of a cylindrical hole (7) common to both bodies, characterized in that the joint comprises a conical second sleeve (9) which is adapted to penetrate into the first sleeve (8), and a bolt (3) running coaxially through the sleeves, whereby, when the bolt is clamped, the second sleeve (9) penetrates, with force, into the first sleeve (8) and forces the first sleeve (8) to expand such that, by deformation of deviations in the hole (7) , the first sleeve (8) makes butt contact with the common hole wall.

2. A bolt joint according to claim 1, characterized in that the first sleeve (8) has a cylindrical outside and a conical inside and that the second sleeve (9) has a conical outside, which conical surfaces cooperate such that, when the second sleeve is pressed into the first sleeve, the first sleeve expands cylindrically.

3. A bolt joint according to claim 1 or 2 , characterized in that the first sleeve (8) has longitudinal slits (10) such that it easily expands during mounting and contracts during dismantling, respectively.

4. A bolt joint according to claim 3, characterized in that the slit (10) of the first sleeve is wave-shaped such that the edge on both sides of the slit exhibits fingers which penetrate into recesses in the opposite edge.

5. A method in an industrial robot for fixing a first body (1) to a second body (2), such that a torsional force acting between the bodies is transmitted in a non-play manner between the bodies, whereby an expandable conical first sleeve (8) is brought to make contact with a hole wall of a cylindrical hole (7) common to both bodies, characterized in that a conical second sleeve (9) is adapted to penetrate into the first sleeve (8) and that a bolt (3) is arranged coaxially through the sleeves, whereby, when the bolt is clamped, the bodies (1, 2) are fixed and the second sleeve (9) is brought to penetrate, with force, into the first sleeve (8) such that the first sleeve is brought to expand, whereby deviations in the hole are deformed such that the first sleeve is brought to make butt contact with the common hole wall .