Surface-machining assembly comprising an effector to be mounted on a robot arm and at least one effector bearing element by means of which the effector bears on the surface and/or on the tools with a ball joint provided therebetween

Abstract

The present application relates to a machining assembly comprising an effector intended to be mounted on a robot with multiple degrees of freedom, in which invention the mounting of the motor spindle relative to the intermediate supports and frame of the effector allows a numerically controlled movement along three axes X, Y, Z of a trihedron, the effector bearing on the piece to be machined or on the surrounding tools by means of a ball joint at the foot end of the effector. Since the effector bears on the piece to be machined or on the surrounding tools it is possible to create local stiffness and to obtain the precision required to guarantee the quality of the machining process.

Claims

1. A surface-machining assembly, comprising: an effector comprising: an electrospindle comprising a body with at one of its ends means for coupling to a cutting tool (O), a first support connected to the body of the electrospindle by a sliding connection allowing movement in translation of the electrospindle along the rotation axis Z of the tool, a second support connected to the first by a sliding connection allowing movement in translation of the first support along an axis X perpendicular to the rotation axis Z of the tool, a chassis one end of which constitutes a foot and the other end of which constitutes a head adapted to be coupled to the free end of a robot arm, the chassis being connected to the second support by a sliding connection allowing movement in translation of the second support along an axis Y perpendicular both to the translation axis X of the first support and the axis Z of translation of the electrospindle and of rotation of the tool; at least one element enabling the foot of the effector to bear on the surface to be machined or on tools that support the surface, the bearing element and the foot of the effector being configured so that the effector is connected to the surface to be machined by a ball joint connection when the foot of the effector is bearing on the surface.

2. The assembly as claimed in claim 1, wherein the end of the foot of the effector is constituted of a ball joint mounted inside a part and defining between them the ball joint connection, the part defining a bearing connection against the surface to be machined or against the tools.

3. The assembly as claimed in claim 1, wherein the end of the foot of the effector is conformed as a part-spherical dome, each bearing element being a stud in the form of a part-spherical dome, arranged on the surface to be machined or against the tools, the shape of the stud being complementary that of the end of the foot of the effector and defining the ball joint connection.

4. The assembly as claimed in claim 1, wherein the end of the foot of the effector is frustoconical, each bearing element being a stud in the form of a part-spherical dome, arranged on the surface to be machined or against the tools, the shape of the stud being complementary to that at the end of the foot of the effector and defining the ball joint connection.

5. The assembly as claimed in claim 3, comprising one or more studs formed integrally with the tools around the surface to be machined.

6. The assembly as claimed in claim 3, comprising one or more studs placed on the surface to be machined or on the tools around it.

7. The assembly as claimed in claim 1, wherein an angular amplitude of the ball joint connection is between ±10 and ±45° inclusive.

8. The assembly as claimed in claim 1, wherein the first support supports the driving device in translation along the axis Z, the second support supports the driving device in translation along the axis X, and the chassis supports the driving device in translation along the axis Y.

9. The assembly as claimed in claim 1, wherein each drive device in translation is a motor connected to a ball screw and nut system or a screw system with satellite rollers.

10. A machining installation comprising a robot with six degrees of freedom, termed a six-axis robot, and an assembly as claimed in claim 1, the head of the effector being coupled to the free end of the arm of the six-axis robot.

11. A method of machining a surface executed by the installation according to claim 10, comprising the following steps: a/ measuring the positions of the centers of the bearing surfaces of each of a plurality of studs; b/ integrating the plurality of studs onto the tools to be placed around the surface to be machined; c/ resting the effector foot on one of the studs and then machining the surface part in the vicinity of said stud, by means of a cutting tool coupled to the electrospindle, the machining being carried out with movement of the electrospindle in translation along the axis X and/or Y and/or Z and/or with rotation of the effector around the center of the ball joint and/or with rotation of the effector around its axis passing through the center of the ball joint and the center of the flange fixing the head to the arm of the robot; d/ successively moving the effector by means of the robot so as to repeat the step c/ with the effector foot bearing on each of the plurality of studs, in order to execute the required machining of the whole surface.

12. The assembly as claimed in claim 1, wherein the ball joint connection allows rotation of the effector about two rotation axes, said rotation being relative to the surface to be machined.

13. A surface-machining assembly, comprising: an effector comprising: an electrospindle comprising a body with at one of its ends means for coupling to a cutting tool (O), a first support connected to the body of the electrospindle by a sliding connection allowing movement in translation of the electrospindle along the rotation axis Z of the tool, a second support connected to the first by a sliding connection allowing movement in translation of the first support along an axis X perpendicular to the rotation axis Z of the tool, a chassis one end of which constitutes a single foot and the other end of which constitutes a head adapted to be coupled to the free end of a robot arm, the chassis being connected to the second support by a sliding connection allowing movement in translation of the second support along an axis Y perpendicular both to the translation axis X of the first support and the axis Z of translation of the electrospindle and of rotation of the tool; at least one element enabling the single foot of the effector to bear on the surface to be machined or on tools that support the surface, the bearing element and the single foot of the effector being configured so that the effector is connected to the surface to be machined by a ball joint connection when the single foot of the effector is bearing on the surface.

Description

DETAILED DESCRIPTION

(1) Other advantages and features of the invention will emerge more clearly on reading the detailed description of embodiments of the invention given by way of nonlimiting illustration with reference to the following figures, in which:

(2) FIG. 1 is a diagrammatic view in partial longitudinal section of an effector according to the invention bearing on the surface to be machined or the tools that support it;

(3) FIG. 1A is a detail view showing the possible relative movement of the cutting tool mounted on the effector and the position relative to the center of the ball joint connection according to the invention at a given rotation position around the axis Z;

(4) FIG. 2 is a diagrammatic top view of the effector from FIG. 1;

(5) FIG. 3 is a detail view in partial section of the end of a foot of the effector according to a first embodiment of the invention employing a ball joint;

(6) FIG. 4 is a diagrammatic perspective view of the end of the effector, intended to come to bear successively against a series of studs integrated into the tools of a surface to be machined, defining a ball joint connection according to a second embodiment of the invention;

(7) FIG. 5 is a diagrammatic perspective view showing a variant embodiment of the foot of the effector.

(8) It is specified here that in the entirety of the present application the terms “lower”, “upper”, “over”, “under”, “interior”, “exterior”, “internal” and “external” are to be understood with reference to an effector according to the invention with its chassis and the cutting tool that it supports arranged on top of the surface S to be machined.

(9) The assembly according to the invention designated overall by the reference 1 comprises first of all an effector 2.

(10) The effector comprises first of all a machining electrospindle 3 the body 30 of which comprises at one of its ends means for coupling to a cutting tool O.

(11) By way of illustrative example, the machining electrospindle 3 may have the following features:

(12) diameter 80 mm,

(13) nominal power rating 7 kW,

(14) nominal rotation speed 25000 rpm,

(15) nominal output torque 5 mN.

(16) It may equally be an electrospindle of 150 mm diameter, nominal power rating 11 kW, nominal rotation speed 12000 rpm, and nominal torque of the order of 10 mN.

(17) The effector 2 also comprises a first support 4 connected to the body 30 of the electrospindle by a sliding connection 5 allowing movement in translation of the electrospindle along the rotation axis Z of the cutting tool O. As in the example shown, this sliding connection 5 can be provided by means of two male structural sections 31 fastened to the body 30 of the electrospindle and each cooperating with a female structural section 40 fastened to the first support 4.

(18) A second support 6 is connected to the first support 4 likewise by a sliding connection 7 allowing movement in translation of the first support 4 along an axis X perpendicular to the rotation axis Z of the tool. As in the example shown, this sliding connection 7 can be produced by means of two male structural sections 60, fastened to the second support 6 and each cooperating with a female structural section 41 fastened to the first support 4.

(19) Finally, the effector 2 comprises a chassis 8 of U or C general shape. One of the ends of the chassis 8 constitutes a foot 80 and the other of its ends constitutes a head 81 adapted to be coupled to the free end of a multi-articulated robot arm, notably of a six-axis robot not shown.

(20) The chassis 8 is connected to the second support 6 by a sliding connection (9) allowing movement in translation of the second support along an axis Y perpendicular both to the axis X of translation of the first support and the axis Z of translation of the electrospindle and rotation of the tool. As in the example shown, this sliding connection 9 may be produced by means of two male structural sections 84 fastened to the chassis and each cooperating with a female structural section 61 fastened to the second support 6.

(21) Each of the structural members for producing the various sliding connections 5, 7 and 9 can for example be produced integrally with or welded or stuck or screwed to the components.

(22) According to a first embodiment shown in FIG. 3, the end of the foot 80 comprises a ball joint 82 mounted inside a plane bearing part 83, defining a ball joint connection between them. Accordingly, thanks to the foot with ball joint 82 in series with the plane bearing part 83, the effector 2 is connected to the surface to be machined by a ball joint connection 11 when the foot of the effector bears on the surface.

(23) According to a second embodiment shown in FIG. 4, the end of the foot 80 is conformed as a part-spherical dome that is complementary to that of a series of studs 10 integral with or mounted along the surface S to be machined or preferably on the tools that support it. Accordingly, the foot 80 of the effector bearing against one of the studs 10 defines with the latter the ball joint connection 11 according to the invention.

(24) The assembly 1 according to the invention enables movement of the effector 2 along the three interpolated linear axes X, Y, Z with two rotation axes A and B obtained thanks to the movements of the robot causing the effector to pivot about the center of the ball joint 11, complemented by the real time movements of the linear axis, so as to obtain a position of the cutting tool O compatible with offline (RTCP) programming, at the tip of the tool.

(25) Moreover, the movements of the robot enable there to be imparted to the effector 2 a movement of rotation about its axis, defined as passing between the center of the ball joint 11 and the center of the flange for fixing the head 81.

(26) By way of illustration, the dimensions Dx, Dy and Dz are for example respectively equal to 700 mm, 650 mm and 700 mm.

(27) Also by way of illustration, the travel C0 of the cutting tool that it is possible to obtain can be of the order of 100 mm and the distance A between the center of the ball joint 11 and the point of maximum separation of the cutting tool can be equal to 250 mm.

(28) Finally, with a cutting tool of 20 mm diameter, the load capacity at the tool can be 100 daN, in the case of the first embodiment with the effector foot including the integral ball joint connection. The load capacity can be higher in the case of the second embodiment, i.e. with the effector bearing on part-spherical studs 10.

(29) Although not shown, different drive systems are fastened to the first support 4, the second support 6 and the chassis 8 of the effector to provide the movement in translation along the axis Z, along the axis X and along the axis Y, respectively.

(30) The inventors have already defined the first dimensioning elements for a machining robot for which an effector according to the invention would be suitable. Two examples of dimensions are indicated hereinafter in relation to industrial robots already commercially available.

Example 1

The Base of the Robot is a “Kuka KR 500” Six-Axis Robot

(31) The load at the cutting tool of approximately 100 daN is absorbed by the plane bearing part 83 in contact with the surface to be machined, which must be applied to that surface with a normal force of 250 daN, considering a mean coefficient of adhesion of the order of 0.4 to prevent slippage.

(32) The spindle 6 of the robot must be of the play compensation type and pre-loaded in the case of machining with a vertical or horizontal spindle.

(33) The reducers of the axes 4 and 6 must therefore be capable of absorbing a torque C corresponding to the equation:
C=(max load at tool)*(maximum distance A between center of ball joint 11 and point of maximum separation of cutting tool).

(34) It is assumed that the stiffness of the reducers is such that, when loaded by the torque C, the resulting movement of the tip of the cutting tool remains less than the machining tolerances, for roughing or finishing.

(35) Accordingly, with the above illustrative data, the torque C of the reducers must be equal to 100 daN×250 mm, that is to say 250 mN.

Example 2

The Base of the Robot is a “Staübli TX200” Six-Axis Robot

(36) Assuming a bearing force of 100 daN transmitted by the robot, which corresponds to the nominal capacity of the robot, the load at the tool must remain below 40 daN, taking into account a coefficient of adhesion of the order of 0.4, and the torque of the cutting tool (spindle) must remain below 3.2 mN.

(37) Accordingly, with the above illustrative data, the reducers for the supports 4 and 6 must therefore be capable of absorbing a torque C equal to 40 daN×250 mm, that is to say 100 mN.

(38) Other variants and advantages of the invention may be produced without departing from the scope of the invention.

(39) In particular, there may be produced, instead and in place of an effector foot 80 in the form of a part-spherical dome bearing against studs 10 of part-spherical shape, an effector foot 80′ of frustoconical shape that can also come to bear against one of the part-spherical studs 10 and define the ball joint connection 11 according to the invention, as shown in FIG. 5.

(40) This variant embodiment of FIG. 5 is advantageous because the frustoconical shape of the effector foot 80′ bears against each part-spherical stud 10 along a line.

(41) The invention is not limited to the examples that have just been described; features of the examples shown may notably be combined with one another in variants that are not shown.