WO2021220142A1

WO2021220142A1 - Devices and method for calibrating industrial robots

Info

Publication number: WO2021220142A1
Application number: PCT/IB2021/053439
Authority: WO
Inventors: Giulio Rosati; Amedeo TODESCHINI; Nicola COMAND; Matteo BOTTIN
Original assignee: Universita' Degli Studi Di Padova
Priority date: 2020-04-30
Filing date: 2021-04-27
Publication date: 2021-11-04
Also published as: IT202000009514A1

Abstract

The present invention relates to a tool (1), an element (2) and a method for calibrating an industrial robot (R), wherein said tool (1) comprises a body (11) so shaped as to allow the coupling with said industrial robot (R), an elongated tip (12) having an end which can exit or enter said body (11) and which can be engaged into a hole of a calibration element (2) positioned on a work plane (P); such tip is actuated by actuator means (13) configured to extend it outwards from the body (11) of said tool (1) and by stopping means (14) configured to stop the sliding thereof with respect to the body (11) of said tool (1), and wherein the movement of said tip (12) away from or towards the body (11) of the tool (1) is detected by detection means (15).

Description

TITLE : "DEVICES AND METHOD FOR CALIBRATING INDUSTRIAL ROBOTS"

DESCRIPTION :

The present invention relates to a tool, an element and a method for calibrating a mechatronic system; in particular, for calibrating an industrial robot.

As is known, industrial robots are equipped with a plurality of positioning systems, as described in United States patent publication no. US 8,457,790 B2 to ZIMMER INC.; typically, an industrial robot comprises a first positioning system made up of a plurality of encoders, each one positioned on one of the joints, so as to detect the robot configuration, and a second positioning system, normally a visual one, which detects the position of and the displacements undergone by the objects positioned on a work plane whereon the industrial robot is carrying out operations like, for example, movements, machining operations, feeling operations, etc.

The presence of such positioning systems requires the execution of a calibration process, so that the industrial robots can carry out the operations with a sufficient level of precision and accuracy to comply with the design requirements of a robotic island.

This process is typically carried out by mounting a feeler on the terminal part of the industrial robot (i.e. where the tool is mounted) for calibrating the positioning system along the Z- axis, i.e. the axis which is perpendicular to the work plane of the industrial robot, after which said feeler is dismounted and replaced with a (rigid) tip for calibrating the positioning systems along the X-axis and Y-axis, i.e. the axes which are parallel to the work plane.

The replacement of the feeler with the tip introduces uncertainty, thus reducing the precision and the accuracy of the calibration operation, in addition to often requiring the intervention of an operator; as a matter of facts, the mounting and dismounting operations add uncertainty to the process, because of the mechanical plays due to the physical characteristics of the coupling flange and to the fact that the two tools will surely show some differences caused by manufacturing tolerances. Moreover, because of robot positioning repeatability errors, the acquisition of the calibration data with the tip at a point where the feeler was previously used introduces a further calibration error, since the two readings are actually made at two different physical points.

United States patent publication no. US 6,205,839 B1 to ASEA BROWN BOVRERI AB describes an equipment for calibration of an industrial robot which has a plurality of axes of rotation, wherein said equipment comprises a measuring device for rotatable connection to a reference point, the position of which is known, and a gravity sensor which is so mounted that its axis is substantially parallel to the axis of rotation of the measuring device, so as to measure the angle between the gravity vector and the axis of rotation.

United States patent publication no. US 4,485,453 to INTERNATIONAL BUSINESS MACHINES CORP. describes a centering device so shaped that it can be coupled with a tip of a tool of a numeric control machine, so as to allow determining with certainty one or more positioning coordinates of said numeric control machine.

The present invention aims at solving these and other problems by providing a calibration tool and a calibration element.

Moreover, the present invention aims at solving these and other problems by providing also a method for calibrating a mechatronic system.

The basic idea of the present invention is to provide a calibration tool having a body so shaped as to allow the coupling of the tool with a mechatronic system, such as, for example, an industrial robot or a numeric control machine, wherein said tool comprises an elongated tip having an end which is movable away from and towards said body and which can be engaged into a hole of a calibration element positioned on a work plane; such tip is actuated by actuator means configured to extend it outwards from the body of said tool, and by stopping means configured to stop the outward extension thereof from the body of said tool, and wherein the movement of said tip away from and towards the body of the tool is detected by detection means.

When this tool is coupled with the mechatronic system and the calibration element is lying on the work plane, it is possible to execute a calibration method that comprises the following steps:

- a positioning phase, wherein the calibration tool is positioned in such a way that said tip approaches a hole compatible with said tip and comprised in the calibration element;

- a coupling phase, wherein said tip is extended by a known length, thus engaging into the hole of the calibration element, so as to possibly displace said calibration element on the work plane;

- a first acquisition phase, wherein a first position datum is acquired by means of a first detection system integral with the mechatronic system, wherein said first position datum describes a position of the tip when it is coupled with the hole of the calibration element;

- a second acquisition phase, wherein a second position datum is acquired by means of a second detection system integral with the work plane, wherein said second position datum describes a position of the hole of the calibration element after said hole has been coupled with the tip of the calibration tool;

- a calculation phase, wherein calibration data, which define a relationship between the first detection system and the second detection system, are computed on the basis of said first position datum and said second position datum.

In this way, it is possible to make a calibration along three axes (C,U,Z) in a single operation. Furthermore, this method ensures a faster, more precise and more accurate calibration because the calibration process can be carried out without changing the tool and at the same physical point for all the axes taken into consideration.

Besides, this method can be executed at a plurality of points on the work plane by coupling the tip of the calibration tool with the hole of the calibration element and by automatically moving said calibration element to the desired points on the work plane.

In this manner, in addition to improving the calibration along the three axes (C,U,Z), it is also possible to automatize almost the entire calibration operation over the whole work plane.

Further advantageous features of the present invention will be set out in the appended claims.

These features as well as further advantages of the present invention will become more apparent in the light of the following description of a preferred embodiment thereof as shown in the annexed drawings, which are provided merely by way of non limiting example, wherein:

- Fig. 1 shows a perspective view wherein a calibration tool according to the invention is coupled with an industrial robot and a calibration element according to the invention is lying on a work plane;

- Fig. 2 shows a front view, a side view and a perspective view of the calibration tool of Fig. 1;

- Fig. 3 shows the calibration tool of Figs. 1 and 2 during the various phases of the method according to the invention;

- Fig. 4 shows a perspective view of a first variant of the calibration tool and calibration element of Fig. 1.

In this description, any reference to "an embodiment" will indicate that a particular configuration, structure or feature is comprised in at least one embodiment of the invention. Therefore, expressions such as "in an embodiment" and the like, which may be found in different parts of this description, will not necessarily refer to the same embodiment. Moreover, any particular configuration, structure or feature may be combined as deemed appropriate in one or more embodiments. The references below are therefore used only for simplicity's sake, and shall not limit the protection scope or extension of the various embodiments .

With reference to Fig. 1, the following will describe a calibration system SC for a mechatronic system operating on a work plane P, wherein said mechatronic system is preferably an industrial robot R, i.e. a multi-axis numeric control machine having an open or closed kinematic chain.

The calibration system SC according to the invention comprises a calibration tool 1 and a calibration element 2 according to the invention.

The industrial robot R comprises a plurality of connection elements (commonly called members or links) R0-R6 and a plurality of joints J1-J6 forming a kinematic chain, wherein the first member R0 is preferably constrained to the floor, while the last member R6 is so shaped that it can be coupled with a tool like the one of the invention. Each joint J1-J6 comprises an encoder that generates a series of signals that encode the extent and direction of the movement made by said joint. Such signals are received by a control unit CU (which may be either comprised in said robot R or separate from said robot R) and are then processed in order to know the configuration of the robot, and hence the position of the tool 1. In other words, the control unit CU comprises processing means (such as, for example, a CPU, a microcontroller or the like) configured to implement the functions of a (first) positioning system (hereafter also referred to as "first positioning system") integral with the robot R, thus generating, on the basis of the signals generated by the encoders, at least one position datum that describes the position of the tool 1 with respect to an origin point integral with the first rigid element R0, so that the position of the tool 1 can be controlled; typically, the selected origin point is a point lying on the floor under the base of said first rigid element R0.

In this embodiment, the robot R has six joints J1-J6 that join seven members R0-R6. It must be pointed out that the number of joints and/or the number of members may also be smaller or greater than those of the example described herein, without however departing from the teachings of the present invention.

It must also be highlighted that the joints J1-J6 may be either of the revolute type or of the non-revolute type (e.g. prismatic, cylindrical, helical, spherical, etc.), without however departing from the teachings of the present invention.

Moreover, the control unit CU is also in signal communication with supervision and check devices (e.g. one or more video cameras) acting as a (second) positioning system (hereafter also referred to as "second positioning system") integral with the work plane P, thus generating, on the basis of the signals generated by the supervision and check devices, at least one (second) position datum that describes the position of an object lying on said work plane P with respect to an origin point integral with said plane P.

Also with reference to Fig. 2, the calibration tool 1 comprises the following parts:

- a body 11 so shaped as to allow the coupling of the tool with the mechatronic system. For this purpose, the body 11 preferably comprises a flange 112 (preferably of standardized shape and dimensions), which permits the coupling with the end-effector seat of the industrial robot R; an elongated tip 12 configured to move away or towards said body 11, wherein an end of said tip 12 can be engaged into a hole of the calibration element 2 positioned on the work plane P; actuator means, e.g. a spring 13, coupled with said body 11 and with said tip 12, and configured to move said tip 12 away from the body 11 of said tool 1; stopping means 14 configured to stop the outward movement, i.e. the sliding, of said tip 12 with respect to the body 11 of said tool 1; detection means, e.g. a linear encoder 15 coupled with a reading scale 114 comprised in (and integral with) the body 11, configured to detect the outward or inward movement, i.e. the sliding movement, of said tip 12 with respect to the body 11 of the tool 1.

In order to ensure a precise relative sliding motion between said tip 12 and the body 11 of said tool 1, the tool 1 preferably comprises sliding means which comprise, for example, a linear slide 17 and a block 18 coupled with each other, wherein one end of said linear slide 17 is integral with the tip 12, and wherein the block 18 is, as will be further described below, attached to the body 11, e.g. by welding, screws or the like.

The body 11 also comprises a main portion 111, preferably having a cylindrical shape, with a first end where the flange 112 is positioned and a second end from which a protrusion 113 extends, which comprises the block 18 of the linear slide 17.

The calibration tool 1 may also comprise a support 16, preferably an L-shaped one, wherein said support 16 comprises a first portion 161 coupled with a lateral surface of the protrusion 113 via the linear slide 17, and a second portion 162 which is orthogonal to said first portion 161; such support 16 is positioned in a manner such that the second portion 162 faces towards an apical surface 113a comprised in the protrusion 113.

The tip 12 is preferably coupled with the second portion 162 of the support 16. This allows said tip 12 to move away and towards the body 11 of the tool 1. The spring 13 is preferably positioned between the apical surface 113a of the protrusion 113 and the second portion 162 of the support 16, wherein said apical surface 113a and said second portion 162 may advantageously be so shaped (e.g. by milling) as to create housing seats in which the ends of said spring 13 can be positioned; in this way, the spring 13 can generate a force that, when the stopping means 14 are not active, will move the support 16, and hence the tip 12, away from the body 11 of the tool 1.

The stopping means 14 preferably comprise a pneumatic piston integral with the body 11 and so oriented that, when said pneumatic piston is actuated, its head will partly come out of a hole 115 of the protrusion 113 of the body 11, abutting on the first portion of the support 16 or on the sliding member of the linear slide 17, thus blocking by friction the outward (or inward) movement of the tip 12 relative to the body 11 of the tool 1. It is thus possible to stop the movement of the tip 12 at any point along its travel.

Furthermore, the stopping means 14 preferably comprise a mechanical limit switch integral with the first portion of the support 16, wherein said mechanical limit switch is configured in such a way that the maximum extension movement of the first portion 161 is compatible with the maximum readable length of the linear encoder 15, so as to preserve the reading ability and the integrity of both the latter and the tool 1 as a whole.

It must be pointed out that the stopping means, the detection means, the sliding means and the actuator means may be different from those described above, or may be configured differently than described above, without however departing from the teachings of the present invention. For example, the block 18 may be connected to the portion 161 of the support 16 and the linear slide 17 may be connected to the protrusion 113, thus de facto exchanging positions in comparison with the above- described configuration. The calibration element 2 comprises a main body preferably having a discoid shape, which can be laid on a work plane; such main body comprises a hole compatible with the tip 12 of the tool 1.

In the preferred embodiment, the tip 12 has a conical, preferably truncated conical, shape, so as to allow for a progressive coupling with the hole 21 of the element 2. Therefore, the downward movement of the tip 12 (under the action of the actuator means 13 and/or the actuators of the mechatronic system) generates a force that drags the calibration element 2 into a position where the tip 12 and the hole 21 of said calibration element 2 are coaxial.

Also with reference to Fig. 3, the following will describe the calibration method according to the invention, which is carried out when the tool 1 is coupled with the industrial robot R (or another type of mechatronic system) and the calibration element is lying on the work plane P.

It must be pointed out right away that, upon the first execution of the calibration method, the tip 12 can preferably be brought to a predefined length by executing the following steps:

- deactivating the stopping means 14, so that the tip 12 will reach its maximum extension;

- positioning the robot in such a way that the tip 12 of the calibration tool 1 and the hole 21 of the calibration element become coaxial; this positioning may be effected, for example, by an operator manually moving the joints J1-J6 of the robot R, or by said operator sending commands to the control unit CU via a manual control interface (e.g. the Teaching Control Pendant of the industrial robot), or by means of commands contained in a specially designed program;

- lowering the robot R towards the work plane until the coupling between the tip 12 and the calibration element 2 is achieved, and applying pressure to the tip 12 (Fig. 3(a)), so that said tip will reach the predefined length (e.g. 10 mm), by pushing the tip 12 against the calibration element 2 on the work plane P;

- activating the stopping means 14, so that the tip 12 will maintain the reached extension and can be moved away from the calibration element 2 (Fig. 3(b)) by means of a suitable movement of the robot R away from the work plane P, without producing any movement of the calibration element 2.

In this way it is possible to cause the tool 1 to take a predefined length; such length is preferably equal to that of the end-effector that will be used after the calibration process. The effectiveness of the calibration process can thus be increased. In fact, the mechatronic system will operate, after the calibration process, at the same height - measured above the surface of the work plane P - as the one used during the calibration phase.

The calibration process according to the invention comprises the following phases:

- a positioning phase (Fig. 3(c)), wherein the tool 1 is positioned in such a way that said tip 12 approaches the hole of the calibration element 2; preferably, the robot R makes a lateral sliding movement, in a direction parallel to the work plane P, thereby dragging the calibration element 2 to the chosen calibration point;

- a coupling phase (Fig. 3(d)), wherein said tip 12 is extended, by means of the actuator means 13 (preferably with the stopping means 14 deactivated), thus engaging into the hole of the calibration element 2, so as to possibly displace said calibration element 2 on the work plane P;

- a first acquisition phase, wherein a first position datum is acquired by means of the first detection system integral with the robot R, wherein said first position datum describes a position of the tip 12 when it is coupled with the hole 21 of the calibration element 2;

- a second acquisition phase, wherein a second position datum is acquired by means of the second detection system integral with the work plane P, wherein said second position datum describes a position of the hole of the calibration element 2 after said hole has been coupled with the tip 12 of the tool 1;

It is thus possible to carry out the calibration along three axes (C,U,Z) in a single operation, thereby making the calibration not only faster, but also more accurate. In fact, the position data along the three axes are acquired at the same physical point, which would be impossible to do when using a feeler and a tip separate from each other, which necessarily require the execution of two successive robot positioning operations, resulting in errors due to the robot position repeatability error. Moreover, this method ensures a faster calibration, because the calibration process can be carried out without changing the tool.

The (first) position datum acquired by means of the first positioning system represents the position of the tip 12, preferably by means of three floating-point values, each one representing a coordinate in the reference system used by the first positioning system. This position datum is computed by the control unit CU on the basis of the configuration of the encoders positioned in the joints J1-J6 and the distance of the tip 12, detected by the detection means 15.

The (second) position datum acquired by means of the second positioning system represents the position of the hole of the calibration element 2, preferably as three floating-point values, each one of which represents a coordinate in the reference system used by the second positioning system.

In addition to the above, the method according to the invention may also comprise a pressing phase to be carried out after the coupling phase and before the first acquisition phase, wherein the mechatronic system applies pressure to the tip 12, thereby restoring a predefined length of the calibration tool 1, which length is detected by detection means, such as the linear encoder 15. In other words, during the first coupling phase the calibration tool 1 is brought to a predefined length by applying a force generated by a movement of the mechatronic system R.

It is therefore possible to execute the first acquisition phase with said tool 1 advantageously having always the same length, so as to increase the precision of the calibration data thus obtained.

In addition to the above, the method according to the invention may also comprise a disengagement phase to be executed after the first acquisition phase and before the second acquisition phase, wherein the tip 12 is disengaged from the hole 21 of the element 2 by means of a suitable movement of the mechatronic system. Such movement must move the body 11 away from the surface of the work plane P.

In this manner, the detection field of the second positioning system can be fully cleared prior to executing the second acquisition phase. This operation is necessary when the mechatronic system R, in the position where the tip 12 is coupled with the hole 21, interferes with the second positioning system, thus reducing the accuracy of the acquired data.

In addition to the above, the control unit CU can be configured for activating, whether at the beginning or during the (optional) disengagement phase, the stopping means 14 so that the tip 12 will not remain coupled with the hole 21 of the calibration element 2 while moving the body 11 away from the surface of the work plane P. This will prevent the calibration element 2 - the position of which must be acquired during the subsequent second acquisition phase - from being displaced from the position reached during the coupling with the tip 12, thereby advantageously avoiding the introduction of any errors due to an imperfect movement of the kinematic chain of the mechatronic system R away from the work plane.

As aforementioned, the second positioning system is preferably of the visual type, i.e. it is a system that generates the (second) position datum on the basis of one or more video signals generated by one or more video cameras framing the work plane P, by using an image recognition algorithm well known in the art. To do so, the second positioning system must preferably recognize the contour of the calibration element 2 and determine the position of the hole of such element 2 on the basis of the position of the element 2 and its geometric characteristics, e.g. the distance of the hole from the edge of such element 2.

As partly mentioned above, in the preferred embodiment the element 2 has a discoid shape, with the hole in the center, wherein the bottom of such hole lies at a predefined height (e.g. 2 mm) above the base of such element. Therefore, in the preferred embodiment the geometric characteristics may comprise the distance of the hole from the edge of the element 2 and/or the height of the bottom of the hole above the base of the element 2.

As an alternative to or in combination with the above, the second positioning system may also be configured for determining the position of the hole on the work plane P ( axes X and Y) by recognizing predefined marks drawn or carved on the surface of said element.

The calibration data may be parameters of a model that models, via an interpolating function, the differences between the different reference systems used by the two positioning systems.

Alternatively, the calibration data may also consist of maps allowing the control unit CU to know, for each point on the work plane P, a correspondence between the two different reference systems used by the two positioning systems.

The calibration data may be generated on the basis of the position data by using a regression algorithm, such as, for example, the least squares algorithm, which may be executed by either the control unit CU or an external computer.

In order to generate calibration data that are precise enough to allow the mechatronic system R to be controlled above the work plane P with a sufficiently high level of accuracy to meet the functional requirements of the application, it is necessary to use a plurality of calibration points distributed on the work plane P, e.g. disposed in a grid arrangement on the surface of the plane P; therefore, a set of calibration points containing at least one point can be generated by either the control unit CU or an external electronic processor, e.g. a personal computer, on the basis of the position, size and geometric characteristics of the work plane P. One possible approach involves feeling three points (Fig. 1) to obtain the approximate position of the plane in the reference system of the control unit CU, and then generating the approximate set of calibration points.

In order to generate the calibration data with higher precision, therefore, the control unit CU of the mechatronic system R may be configured to execute, once the set of calibration points has been generated and the first point has been acquired by means of the above-described procedure, the following additional phases:

- a disengagement phase, wherein the tip 12 is partially disengaged from the hole 21 of the element 2;

- a displacement phase, wherein the tip 12, after the acquisition phase, is moved into a new position, preferably on the basis of said set of calibration points; at the same time, the calibration element 2 is advantageously dragged parallel to the work plane P (Fig. 3(c));

- a second coupling phase, wherein said tip 12 is extended, by means of the actuator means 13 (preferably with the stopping means 14 deactivated), thus engaging into the hole 21 of the calibration element 2, so as to possibly displace said calibration element on the work plane P;

- a second pressing phase (optional), wherein the robot R exerts pressure on the calibration element positioned on the work plane P until the length of the calibration tool becomes again equal to the previously set predefined length; such length may be detected by detection means, such as the linear encoder 15;

- a third acquisition phase, wherein a third position datum is acquired by means of the first detection system (integral with the industrial robot), which describes the new position of the tip 12 when it is coupled with the hole 21 of the calibration element 2;

- a fourth acquisition phase, wherein a fourth position datum is acquired by means of the second detection system (integral with the work plane), wherein said fourth position datum describes the position of the hole 21 of the calibration element 2 after said hole 21 has been coupled with the tip 12 of the calibration tool 1.

Furthermore, during the calculation phase the calibration data are computed also on the basis of said third position datum and said fourth position datum.

It must be highlighted that the above-described phases may be repeated for each point included in the set of calibration points, so as to generate more precise and accurate calibration data for a larger portion of the work plane P, and that, prior to executing each (second) coupling phase, the tip 12 may be brought to a predefined length by executing the previously described steps. This makes it possible to automatize the calibration operation at a plurality of points. In this manner, in addition to improving the calibration along the three axes (C,U,Z) by executing a single coupling operation per point, it is possible to automatize almost the entire calibration operation over the whole work plane P.

It must also be pointed out that the disengagement phase for each subsequent point may be executed before the (fourth) acquisition phase. Also, if the second positioning system is capable of detecting the position of the hole 21 of the calibration element 2 when the tip 12 is still coupled with the hole 21 of said element 2 (e.g. when the diameter of the disk is greater than that of the body 11 of the tool 1 and the mechatronic system R does not interfere with the reading), the (fourth) acquisition phase may be executed when the tip 12 of the tool 1 is still coupled with the hole 21 of the calibration element 2.

In addition to the above, the control unit CU can be configured for activating, whether at the beginning or during the disengagement phase, the stopping means 14 so that the tip 12 will not remain coupled with the hole 21 of the calibration element 2 while moving the body 11 away from the surface of the work plane P. This will prevent the calibration element 2 from being displaced from the position reached during the coupling with the tip 12, thereby advantageously avoiding the introduction of any errors due to an imperfect movement of the kinematic chain of the mechatronic system R away from the work plane P.

Besides, this also reduces the time necessary for bringing the length of the calibration tool back to the predefined value during the (optional) pressing phase, thus decreasing the total time required by the calibration procedure.

In this way, it is possible to execute the calibration along three axes (C,U,Z) in a single operation, thereby improving the final result.

Of course, the example described so far may be subject to many variations.

A first variant is shown in Fig. 4; for brevity, the following description will only highlight those parts which make this and the next variants different from the above-described main embodiment; for the same reason, wherever possible the same reference numerals, with the addition of one or more apostrophes, will be used for indicating structurally or functionally equivalent elements.

In this first variant, a calibration element 2 has some characteristics that are different from those of the calibration element 2 of the main embodiment; such characteristics allow the second positioning system (integral with the work plane P) to recognize not only the position of said calibration element, but also its orientation with respect to the work plane P.

In particular, the calibration element 2 may have a prismatic shape, e.g. a prism with a triangular, square, pentagonal, etc. shape. In combination with or as an alternative to such a conformation, the body of the calibration element 2 may also comprise a surface, preferably its top surface where the hole 21' is located, whereon marks are present which permit detecting the orientation of such element 2 .

The term "orientation" preferably refers herein to an angle that a portion of the element 2 (e.g. a side and/or the marks on its surface) forms around the Z-axis of the reference system used by the second positioning system, i.e. the axis of said reference system which is orthogonal to the work plane P, with respect to one of the axes X,Y of said reference system, i.e. the axes of said reference system which are parallel to the work plane P.

In addition to the above, the hole 21' of the calibration element 2 has a pyramidal, preferably truncated pyramidal, shape, e.g. a truncated tetrahedron, a truncated pyramid with a square, pentagonal, etc. base, or the like. Likewise, a tip 12' included in a calibration tool 1' similar to the tool 1 of the preceding embodiment may have a pyramidal, preferably truncated pyramidal, shape compatible with that of the hole 21' of the calibration element 2'.

This makes it possible to produce, during the coupling phase, a (possible) change in the orientation of the calibration element 2', in addition to the change of position already described.

It is thus possible to effect a calibration not only along the axes C,U,Z, but also around the axis orthogonal to the work plane P, i.e. it is possible to calibrate the angle that expresses the orientation of the end-effector of the robot R relative to an axis orthogonal to the work plane P, which angle will be defined herein as "theta angle (Q)".

More in detail, during the acquisition phase of the calibration method according to the invention the first position datum may describe, in addition to the position of the tip 12' when it is coupled with the hole 21' of the calibration element 2', also an orientation thereof when it is coupled with such hole, while the second position datum may describe, in addition to the position of the hole 21' of the calibration element 2' after said hole 21' has been coupled with the tip 12', also an orientation thereof after said hole 21' has been coupled with the tip 12'. It must be reminded that knowing the orientation of the hole 21' of the element 2' also implies knowing the orientation of such element 2'.

Similar considerations also apply to the third position datum and the fourth position datum, which, as described above, may respectively describe the orientation of the tip 12' when it is coupled with the hole 21' of the calibration element 2' and the orientation of the hole of the calibration element 2' after said hole has been coupled with the tip 12'.

By acquiring also this information about the orientation of the tip 12' and of the element 2' it is possible to generate, during the calculation phase, calibration data that define a relationship between the first positioning system and the second positioning system also as concerns the theta angles (Q) read by said positioning systems. Some of the possible variants of the invention have been described above, but it will be clear to those skilled in the art that other embodiments may also be implemented in practice, wherein several elements may be replaced with other technically equivalent elements. The present invention is not, therefore, limited to the above-described illustrative examples, but may be subject to various modifications, improvements, replacements of equivalent parts and elements without however departing from the basic inventive idea, as specified in the following claims.

Claims

CLAIMS :

1. A calibration tool (1,1') for a mechatronic system (R), comprising

- a body (11) so shaped as to allow the coupling of said calibration tool (1,1') with the mechatronic system (R),

- an elongated tip (12,12') having an end configured to move away from or towards said body (11), and which can be engaged into a hole (21,21') of a calibration element (2,2') positioned on a work plane (P),

- actuator means (13) coupled with said body (11) and with said tip (12,12'), and configured to move said tip (12,12') away from the body (11) of said tool (1),

- detection means (15) configured to detect the sliding of said tip (12,12') with respect to the body (11) of the tool {1,1'), characterized in that it also comprises:

- stopping means (14) configured to stop the sliding of said tip (12,12') with respect to the body (11) of said tool (1,1')·

2. The tool (1,1') according to claim 1, wherein said tip has a conical shape.

3. The tool (1,1') according to claim 1, wherein said tip has a pyramidal shape.

4. A calibration element (2,2') for an industrial robot, comprising

- a body that can be laid on a work plane (P), characterized in that said body comprises a hole (21,21') compatible with a tip (12,120) of a calibration tool (1,1') according to any one of claims 2 to 3.

5. The element (2) according to claim 4, wherein said body has a cylindrical shape.

6. The element (2') according to claim 4, wherein said body has a prismatic shape.

7. The element (2,2') according to claims 5 or 6, wherein the body comprises a surface on which marks are represented which allow detecting an orientation of said element (2,2^f).

8. A method for calibrating a mechatronic system (R) that comprises an industrial robot (R) operating on a work plane (P), comprising a.a positioning phase, wherein a calibration tool (1,1'), which comprises an extendable tip (12,12') and which is mounted in a terminal portion of said industrial robot (R), is positioned in such a way that said tip (12,12') approaches a hole (21,21') which is compatible with said tip (12,12') and which is comprised in a calibration element (2,2') positioned on the work plane (P), b. a coupling phase, wherein said tip (12,12') is extended, by means of actuator means (13), thus engaging into the hole

(21,21') of the calibration element (2,2 '), so as to possibly displace said calibration element (2,2') on the work plane (P), c.a first acquisition phase, wherein a first position datum is acquired by means of a first detection system, which is integral with the mechatronic system (R), wherein said first position datum describes a position of the tip (12,12') when it is coupled with the hole (21,21') of the calibration element (2,2'), and d.a second acquisition phase, wherein a second position datum is acquired by means of a second detection system, which is integral with the work plane (P), wherein said second position datum describes a position of the hole (21,21') of the calibration element (2,2') after said hole (21,21') has been coupled with the tip (12,12') of the calibration tool (l,l^f), e.a calculation phase, wherein calibration data, which define a relationship between the first detection system and the second detection system, are computed on the basis of said first position datum and said second position datum.

9. The method according to claim 8, comprising also f.a disengagement phase, wherein the tip (12,12') is partially disengaged from the hole (21,21') of the element (2,2^f), g.a displacement phase, wherein the tip (12,12') is moved into a new position, h.a second coupling phase, wherein said tip (12,12') is extended, by means of the actuator means (13), thus engaging into the hole (21,21') of the calibration element (2,2'), so as to possibly displace said calibration element (2,2') on the work plane (P), i.a third acquisition phase, wherein a third position datum is acquired by means of the first detection system, which describes said new position of said tip (12,12') when it is coupled with the hole (21,21') of the calibration element (2,2'), and j.a fourth acquisition phase, wherein a fourth position datum is acquired by means of the second detection system, which describes a position of the hole (21,21') of the calibration element (2,2') after said hole (21,21') has been coupled with the tip (12,12') of the calibration tool (1,1')·

10. The method according to claim 9, wherein, during the disengagement phase, the extension of the tip (12,12') is blocked by stopping means (14).

11. The method according to claims 9 or 10, wherein the disengagement phase is performed after the first acquisition phase and before the second acquisition phase.

12. The method according to any one of claims 8 to 11, wherein, during the first and/or second coupling phase, the calibration tool (1) is brought to a predetermined length by applying a force generated by a movement of the mechatronic system (R).

13. A computer program product loadable into the memory of an electronic computer and comprising software code portions for the execution of the phases of the method according to any one of claims 8 to 12.