State of the Art There is normally an attachment means fixed at the end of a robot arm or the like. The attachment means is normally gripping an implement, which implement may be a tool holder, a tool, a gripping means etc. Thus, in this description the expression"implement"is used in a wide sense. The attachment means may also be used to grip articles directly, e. g. for transferring the articles from one position to another. The position of the implement or article to be gripped is normally critical. As the attachment means is placed at the end of an arm the weight of the attachment means is critical. A heavy load at the end of an arm means greater demands on the control of the arm. The implement is normally attached to the attachment means of the prior art in a rather unstable manner. Due to the momentum given by the heavy load and the unstable attachment it has been difficult in the prior art to position the arm exactly. In case of a high demand for an exact position of the arm the solution has for example been to fixate the implement at the robot arm, whereby the flexibility with swift changes of implements is lost.

As an example of prior art, the gripping of the attachment means may be actuated by means of balls being pressed against a mating surface. The balls are pressed against the mating surface by being moved over a cam or the like. The mating surface moved by the balls will grip an implement or the like. One problem with the attachment means of the prior art, is that the maximal force of the

attachment means is limited by the weight and stability of the attachment means. Put in other words, if the attachment means is to be able to handle a heavy load it will be rather bulky.

Summary of the Invention Thus, one object of the present invention is to be able to transfer relatively large forces using equipment (attachment means) having a relatively low weight.

The above object is achieved in that the attachment means is given a special design. A chamber for an incompressible fluid is arranged at the inner or outer diameter of the attachment means. The wall of the chamber closest to the inner or outer diameter of the attachment means is relatively thin. The thin wall is thin enough to bulge if the chamber is pressurised in a certain extent.

Whether the thin wall of the chamber is directed inwards or outwards depend on if the attachment means is to grip from the inside or the outside of the implement. If the attachment means is brought into an opening of the implement or around the implement before the pressurising of the chamber, the attachment means will grip the implement or article when the chamber is subsequently pressurised.

The attachment means of the invention is possible to use with existing robot arms or the like. The only adaptation necessary is that the tool holder or implement has to be adapted to the gripping means of the attachment means.

Brief Description of the Drawinqs The present invention will be described more closely below, by way of an example with reference to the enclosed drawings, in which

Fig. 1 shows a robot arm or the like having the attachment means of the invention, Fig. 2 shows a cross section of a first embodiment for a gripping means of an attachment means of the invention taken along the line A-A of Fig. 1, Fig. 3 shows a cross section of a second embodiment for a gripping means taken along the line A-A of Fig. 1, Fig. 4 shows the end of a robot arm having the attachment means of the present invention and ready for gripping an implement, and Fig. 5 shows the robot arm of Fig. 4 after gripping of an implement.

Description of Preferred Embodiments The expressions"robot arm"and"robot arm or the like"in this description is intended to cover a normal robot but also any machine having at least one part resembling a robot arm. Such machines may be a multipurpose machine, a numerically controlled machine etc.

In Fig. 1 an attachment means 3 according to the invention is shown fixed to a robot arm 1 or the like. The attachment means 3 is normally fixed to an attachment plate 2 of the robot arm 1 by means of a number of fastening means such as screws and nuts (not shown).

The attachment means 3 comprises a gripping means 4.

The gripping means 4 has normally a round cross section but it is possible with other cross section forms. As shown in Figs. 2 and 3 a chamber 6 is arranged inside a thin wall 10 of the gripping means 4. The thin wall 10 is placed at the inner or outer diameter of the gripping means 4 depending on the gripping direction. Normally the chamber 6 goes all around the gripping means 4. The chamber 6 is to receive a fluid that may be pressurised. The fluid is normally some kind of oil or grease. When the fluid of the chamber 6 is pressurised the thin wall 10 of the gripping means 4 will

bulge inwards or outwards depending of where it is placed.

The thin wall 10 has a thickness allowing the bulging without risk of breaking.

The pressurising and depressurising of the chamber 6 is normally controlled by the control system of the robot or the like. But as this control forms no part of the present invention it will not be described further here.

The fluid to the chamber 6 will normally be furnished by means of a hydraulic system of the robot or the like.

The fluid may also be furnished with a separate hydraulic system.

In Fig. 2 a cross section of a first embodiment for a gripping means 4a is shown. The gripping means 4a of Fig. 2 is intended for gripping around an implement such as a tool holder. The gripping means 4a has an inner diameter 7 and an outer diameter 8. The thin wall 10 of the chamber 6 is placed at the inner diameter 7. If the gripping means 4a is placed over an implement 5 or other article when the chamber 6 is pressurised the implement 5 or article will be gripped by the bulging thin wall 10.

In Fig. 3 a second embodiment for the gripping means 4b is shown. The gripping means 4b of Fig. 4 is intended for gripping in an opening 11 of an implement 5. In this case the thin wall 10 is placed at the outer diameter 9 of the gripping means 4b. When the chamber 6 is pressurised the thin wall 10 will bulge outwards. If the gripping means 4b is placed e. g. in a opening 11 of an implement 5 when the bulging of the thin wall 10 occurs the implement 5 will be gripped and may be handled in the intended way.

Thus depending on the design, the gripping means 4 is gripping outwardly or inwardly. This is done by a change of diameter outwardly or inwardly, respectively, in that the thin wall 10 bulge outwards or inwards when the chamber 6 is pressurised.

In Figs. 4 and 5 the operation of the robot arm 1 or the like having the attachment means of the invention is shown schematically. In Fig. 4 the robot arm 1 has moved to a position straight over the opening 11 of one of a number of tool holders 5a-c to be gripped. The control of the robot arm 1 is done by means of the normal control system of the robot or the machine to which the robot arm 1 is attached. The next step is that the gripping means 4b is brought down into the opening 11 of the tool holder 5b.

When the gripping means 4b has stopped inside the opening 11 the chamber 6 is pressurised. A detection means may be arranged to determine if the gripping means 4b is in a correct position for gripping. As the chamber 6 is pressurised the thin wall 10 of the gripping means 4 will bulge outwardly and grip against the inner wall of the opening 11. Now the tool holder 5b may be lifted and brought to the position where it is to perform the desired act, which may be one of a large range of different actions. This is reflected in Fig. 5.

The outer diameter of the gripping means 4 and the inner diameter of the opening 11 of the tool holder 5 are adapted to each other in order to guarantee an accurate gripping of the tool holder 5.

The description above of the gripping means 4b and its operation is in principal the same independent of the position of the chamber 6. Thus, all of the above apply also for the attachment means of Fig. 2 where the gripping is done at the inner diameter 7 of the gripping means 4a.

The design of the gripping means 4 having a chamber 6 for pressurised fluid on the inside of a thin wall 10 gives an attachment means 3 of low weight, capable of lifting heavy loads. As an example, the relationship between lifting capacity and weight of the attachment means of the present invention is improved by a factor 10 to 230 compared to the attachment means of the prior art. The

above range reflects different makes of the attachment means of the prior art. Also the relationship between the ability to withstand bending forces and the weight is improved, by a factor 30 to 260 in this case depending on make.

As the design of the gripping means 4 is simple without any folds or form changes it is very easy to keep clean. It may be enough to flush the gripping means 4 with cutting fluid, water or other suitable fluid. It is also possible to use compressed air.

Existing tool holders or other implements are often fairly simple to adapt to the attachment means 3 of the invention. It is enough to furnish an opening 11 or a cylindrical surface having a diameter adapted to the diameter of the gripping means 4a, 4b.

As the attachment means is of lower weight as compared to existing attachment means for even larger forces the accuracy of the robot arm 1 will increase. Thus, it will be possible to position the robot arm 1 more precisely and faster as compared to the prior art. The existing robots will often have to be calibrated due to becoming offset. This is due to the problems with exact positioning, which often leads to collisions for the robot arm with surrounding parts. The calibration takes time away from the desired operation of the robot arm 1.

As the attachment means 3 of the invention transfers larger force and is of lower weight than the attachment means of the prior art the demands on the robot arm 1 are lower and the precision higher, which means that smaller and thus cheaper robots may be used. It is of course also possible to increase the weight of the tools or other implements when using the same robot, and still have the same precision. A further advantage is that the attachment between implement and attachment means is improved by the present invention. Thus, due to the improvements of the

present invention the robot arm 1 may be positioned at a much higher speed with the same or improved precision.

In order to control the position of the gripping means 4 in relation to the tool holder 5 or implement to be gripped the attachment means may be furnished with a detection means as stated above. The purpose of the detection means is to detect when the gripping means 4 is in the right position for gripping the tool holder 5 or other implement. In one embodiment the detection means has the form of an air jet (stream) coming out from a small hole (not shown) in the bottom surface of the gripping means. As the gripping means 4 is approaching the tool holder 5 the pressure of the air jet will be influenced. By analysing the pressure of the air jet it is possible to establish when the gripping means 4 is in position for gripping the tool holder 5 or any other implement.