WO1980001547A1

WO1980001547A1 - Mechanical device for guiding the relative movement between two movable parts

Info

Publication number: WO1980001547A1
Application number: PCT/SE1980/000024
Authority: WO
Inventors: C Johansson; C Eriksson
Original assignee: C Johansson; C Eriksson
Priority date: 1979-02-02
Filing date: 1980-01-25
Publication date: 1980-08-07
Also published as: SE7900910L; GB2052326B; GB2052326A

Abstract

Machine component and use thereof for assembling parts. The machine component comprises a body (1) which is preferably symmetrical relative to an imaginary line (2) through the body (1). The latter has two shafts (3, 4) which project from the body in opposite directions. From a neutral position in which the centre lines of the shafts coincide approximately with each other and with the line of symmetry (2), the shafts (3, 4) can be moved relative to the body (1). One of the shafts (3) can be moved parallel relative to the line of symmetry (2) and the other shaft (4) can be rotated around a point on the line of symmetry (2). The centre line of the shaft thereby forms an acute angle with the line of symmetry. When the machine component is used for guiding in two parts which are movable relative to each other, one of which is to be fitted into the other, the component helps to prevent the occurrence of the so-called jammed-drawer effect. The part which is to be inserted is held by the machine component and is inserted along a straight line with which the line of symmetry of the machine component is approximately parallel. The said point of the component should coincide substantially with that end of the part which is to be inserted which is located furthest from the component, i.e the end which will be inserted first.

Description

MECHANICAL DEVICE FOR GUIDING THE RELATIVE MOVEMENT BETWEEN TWO MOVABLE PARTS - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

The present invention relates to a machine component for guiding in two parts which are movable relative to each other, of which one is to be inserted in the other, for example, in a drilling or thread-forming machine where a drill or a thread pin is to be moved into a hole, or in an assembly machine or an assembly tool for facilitating the assembly of a unit made up of parts, in which one part is to be assembled with another unit, for example, inserting a bearing or threading a sleeve in a bearing housing or on a shaft respectively, comprising two outer parts from which imaginary reference lines extend, and at least one intermediate part, these parts being movable relative to each other from a neutral position in which the said reference lines coincide at least approximately, in such a way that one outer part can be moved transversally relative to its adjoining intermediate part, i.e. so that the associated reference line is moved parallel, and the other outer part is rotatably movable relative to its adjoining intermediate part, around a point located at a distance from the parts and towards which the reference line appertaining to the latter outer part points constantly.

With both manual and automatic assembly of parts whereby a part is inserted in or threaded on another part with little or no play, problems frequently arise due to the fact that the parts wedge firmly in each other in the same way as a drawer may jam. When assembling with an industrial robot there is the further problem that the tolerances of the parts which are to be mounted are significantly finer than is the accuracy of the reproducibility of the robot, while the risk of errors in the angle between the parts which are to be assembled together is considerable. This results in the parts which are to be assembled tilting and the jammed-drawer effect occurs. The problems touched on briefly above exist not only in robot assembling, but also during pressing in and on operations, for example, when assembling roller bearings and sleeves. In a paper with the title: Precise Insert Operation by Tactile Controlled Robot "HI-T-Hand Expert 2" by Tatsuo Goto, Tadao Inoyame and Klyoo Takeyasu, published in Forceedings of the 4th International Symposium on Industrial Robots, 19th, 20th and 21st November, 19?4 in Tokyo, Japan, these problems are described in detail. In the paper a solution is also described, based on providing an assembly robot with a flexible wrist by means of which, by complicated monitoring of the forces which arise during the assembly process and multi-axis servo-control, an attempt is made to prevent the occurrence of the jasmed-drawer effect. Even if the construction described in the paper is per se a solution of the above-mentioned assembly problems, it is a relatively complicated and therefore expensive solution. The complicated nature of the construction means that the risk of a failure and a consequent loss of production is considerable.

The problem of the jammed-drawer effect in assembly operations like moving a pin into a hole is also dealt with in the American Patent 4,098,001, and in the Patent a wrist-like arrangement is described which is considerably simpler than the wrist described in the above-mentioned paper. The arrangement comprises three parts which are mutually connected one after the other by means of connecting elements so that the middle part and one of the outer parts can revolve relative to each other around a centre point lying at a distance, and the middle part and the other of the outer parts can move translatorily relative to each other. To make these rotating and translatory movements possible the connecting elements are elastic, which means that the position of the centre point varies as the loading of the arrangement varies. Furthermore, the load-bearing capacity of the arrangement is limited.

The aim of the present invention is to provide a machine component of the type described in the introduction which may be used for many applications and does not have the described disadvantages, but which solves in a simple and inexpensive way the problem of the jammed-drawer effect. This is made possible due to the fact that the machine component has the characteristics indicated in the attached Patent Claims.

The invention will be explained further in the following with reference to the attached Drawings, in which Figure 1 shows an embodiment example, partly in section, of a machine component according to the present invention. Figure 2 shows a longitudinal section through, another embodiment example of a machine component according to the invention. Figure 3 shows a way of making the machine component torque-transmitting. Figures 4 and 5 are longitudinal sections through two other embodiments of the machine component. In Figure 6 an application according to the invention of a machine component accordisg to the present invention is shown, and Figures 7a and 7b illustrate the occurrence of the so-called jammed-drawer effect and how this effect is eliminated with the aid of a machine device according to the invention. In the following, parts with a comparable or identical effect have been given the same reference designations.

In the Drawing, 1 is a body which is preferably symmetrical relative to an imaginary line 2 through the body 1. The body has two shafts 3, 4 which extend out in opposite directions. The shaft 3 is movable in that it can be moved parallel relative to the line of symmetry 2, while the shaft 4 is movable in that it can be rotated around a point 5 on the line of symmetry 2. The body 1 comprises at least three parts 6, 7 and 8. Of these, the shaft 3 is associated with the part 6 which is movable relative to its nearest adjacent part 7 over a substantially flat surface 9 orientated transverse to the line of symmetry 2. The shaft 4 is associated with the part 8 and is movable relative to its nearest adjacent part, part 7 on the Drawing, over a substantially spherical surface 10, the centre of curvature of which coincides or almost coincides with the point 5 on the line of symmetry 2. According to the primary characteristic of the invention, the movement between the parts 6, 7 and 8 is effected by direct sliding.

The advantages of the various embodiments will be described briefly with reference to the individual Figures 1 - 6.

The machine component in Figure 1 is comparable in its effect with a radially very flexible but axially rigid shaft. The part 6 is a flat circular plate which can slide with little friction over the flat surface 9. In a similar way, the part 8 is comparable with part of a spherical shell, the centre of curvature of which coincides with the point 5 and which can slide with little friction over the spherical surface 10. According to a particular characteristic of the invention, the movement of the parts 6 and 8 relative to the part 7 is restricted to a predetermined maximum value by means of flanges 11, 12 extending round the periphery of the part 7. By means of annular elements 13 and 14 attached to the flanges 11 and 12 respectively, the parts 6 and 8 respectively are fixed relative to the part 7 so that no relative movement can take place in the direction of the line of symmetry 2.

The embodiment of the machine component according to the invention shown in Figure 2 has members 15, 16 which seek to hold the parts 6, 7 and 7, 8 respectively in a position relative to each other, as indicated in a particularly characteristic of the invention. The said members are made up of springs or, as in the Figure, of elastic elements arranged between the parts 6, 7 and 7, 8 respectively.

According to another special characteristic of the invention, a friction-reducing layer is provided between the parts 6, 7 and 7, 8 respectively.

As indicated in one particular characteristic, the machine component according to the invention can be equipped with members which have the task of resticting the capacity for movement of two adjacent parts to only one plane. In this way, a machine component is obtained which has the ability to transmit torque. Figure 3 shows such an embodiment. The parts 6 and 8 in this case are divided into two parts 6a, 6b and 8a, 8b respectively. The parts 6b and 7, and 8a and 8b are movable relative to each other only in one plane which extends transverse to the plane of the Drawing. This is achieved by a groove 26 in the parts 7 and 8b respectively and a flange 27 which engages in this groove on the parts 6b and 8a respectively. In a similar way, the parts 6a and 6b, and 7 and 8b respectively are movable relative to each other only in a plane parallel with the Drawing. It will be seen that due to the capacity for relative movement between the parts 6a, 6b and 7 and between the parts 7, 8a and 8b respectively, a corresponding function is obtained to that of the component in Figure 1, but with the difference that torque can be transmitted by the machine component shown in Figure 3.

The distinguishing feature of the embodiment of the machine component according to the present invention show in Figures 4 and 5 is that it has a relatively low structural height and that it is made so that the parts contained in the component are very simple and cheap to produce.

In Figure 4, the part 6 consists of two circular plates 6' and 6" fixed firmly on the shaft 3 at a mutual distance corresponding to the thickness of the part 7, which is made of a steel plate pressed into a socket-like shape. The part 7 has a flat part 7' and a spherical part 7". The planar part 7' is mounted so that it can slide between the plates 6' and 6", and the spherical part 7" is mounted so that it can slide in the part 8, which consists of two parts 8', 8" mounted at a mutual distance corresponding to the thickness of the part 7. Viewed in the radial direction, the relative movement parallel to the line of symmetry between the parts 7 and 8 relative to the line of symmetry d takes place further out from the shaft 3.

According to a particular, characteristic of the invention, both the machine components shown in Figures 4 and 5 can .be equipped with an element 28 which acts in such a way that relative rotation between the parts 6 and 8 around the line of symmetry 2 is possible only through a specific angular amount. For example, the element 28 may be made of steel wires stretched between the parts 6 and 8. The magnitude of the said angular amount depends on how slack or tight the wires are.

An application of a machine component according to the present invention will now be described with reference to Figures 6 and 7, namely, facilitating the guiding in of two parts which are movable relative to each other, one of which is to be fitted into or threaded onto the other. A task like this arises, for example, in drilling or thread-forming machines wherein a drill or a thread pin has to be put into a hole. The task also arises with an automatic assembly machine or a manual assembly tool for facilitating the assembly of a unit made up of parts, in which two parts are to be assembled together, such as the insertion of a bearing or the threading of a sleeve in a bearing housing or on a shaft, respectively, for example.

In Figure 6, 29 is the general designation of an assembly robot with two gripping devices 30, 31. With its gripping devices 30, 31 the robot is programmed to collect from a supply which is not shown in detail in the Drawing, the parts 32, 33, of which the parts 32 are provided with a bore, and to transport these parts one by one to an assembly position where the part 33 is to be moved automatically into the bore 34 in the part 32. With the aid of a locating system 35 of a type which is known per se, the gripper device 30 can be made to move in the direction indicated with the arrows 36, 37 and 38 so that the part 33 is located directly above the bore 34, at least immediately before insertion in the latter. For various reasons, including the poor reproducibility of the movements of the gripper devices, a certain amount of inaccuracy occurs with regard to the lining-up of the part 33 relative to the bore 34 in the part 32. This lack of accuracy can be of two types, which may occur simultaneously or individually. Centring errors may occur (see Figure 7a), and angular errors may occur (see Figure 7b), between the centre lines of the parts 33 and the bore 34.

According to the invention a machine component of the type according to the invention which has been described above and with the aid of which the effect of the abovie-mentioned centring and angular errors can be eliminated is arranged between the gripper element 30 and the locating system 35.

A centring error when inserting the part 33 with a force F₀ in the bore 34 results in a horizontal normal force component F₁ (see Figure 7a) which acts on the part 33. Since the parts 6 and 7 in the machine component can move easily relative to each other, the force F₁ immediately moves the part 33 towards a position in which the part 33 and the bore 34 are perfectly centred relative to each other. When there is an angular error a between thepart 33 and the bore 34 (see Figure 7b), the part 33 is influenced by two opposite horizontal force components F₂ and F₃. These would normally have resulted in the part 33 wedging firmly in the bore 34, and the more the force F₀ increased, the harder it would jam. However, the machine component 1 which according to the invention has the rotation point 5 disposed, as explained in connection with Figure 1, so that it substantially coincides with that end of the part 33 which is located furthese away from the gripping device 30, ensures that the angular error a is eliminated. This is effected in the following way: the force F₂ produces on the part 33 a torque around the point 5 which has the magnitude F₂ · l₂ and which tends to reduce the angular error a In the opposite direction, a torque with the magnitude F₃ · l₃ acts, but since l₃ is less than l₂ a restoring torque is obtained. The part 33 is thus set up so that its line of symmetry is parallel with the centre line of the nore 34, and it may easily be inserted therein.

Claims

P a t e n t C l a i m s

1. A machine component for guiding in two parts (32, 33) which are movable relative to each other, one of which is to be inserted in the other (32), for example, in a drilling or thread-forming machine, in which a drill or a thread pin is to be inserted in a hole, or in an assembly machine or an assembly tool for facilitating the assembly of a unit made up of parts where one part is to be assembled with another unit, for example, the insertion of a bearing or the threading of a sleeve in a bearing housing or on a shaft respectively, comprising two outer parts (6, 8) from which imaginary reference lines extend and at least one intermediate part (7), these parts being movable relative to each other from a neutral position in which the said reference lines coincide at least approximately, in such a way that one outer part (6) can be moved transversally relative to its adjoining intermediate part (7), i.e. so that the associated reference line is moved parallel, and the other outer part (8) is rotatably movable relative to its adjoining intermediate part (7) around a point located at a distance from the parts and towards which the reference line of the last-named outerpart (8) points constantly, characterised in that between one of the outer parts (6) and the adjoining intermediate part (7) there is a flat boundary surface (9), that between the other outer part (8) and the adjoining intermediate part (7) there is a spherical boundary surface (10), the centre of curvature of which coincides with the said point, and that relative movements between the parts lying adjacent to each other is effected by sliding between the said surfaces (9, 10).

2. A machine component according to Patent Claim 1, characterised in that the device comprises elements (15, 16) which act between the parts (6, 7, 8) and which seek to hold the parts (6, 7; 7, 8) in a neutral position relative to each other.

3. A machine component according to either of the preceeding Patent Claims, characterised in that there is a friction-reducing layer, made, for example, of polytetrafluorethylene, between the parts (6, 7, 8).

4. A machine component according to any of the preceeding Patent Claims, characterised in that all the parts of the device comprise elements (26, 27) designed to act so that two parts disposed adjacent to each other are movable so that their associated reference lines lie in one plane during the movement.

5. A machine component according to any of the preceeding Patent Claims, characterised in that the component has members (11, 12) designed to restrict the movement between two parts lying adjacent to each other to a predetermined maximum value.

6. A machine component according to any of Patent Claims 2 - 6, characterised in that the body (1) comprises an element (28) effectively connected to the two outer parts (6, 8) and acting in such a way that relative rotation between the parts is possible only through a specific angular amount, which means that the component has the ability to transmit torque after the relative rotation has attained the said angular amount.