WO2015055782A1 - Scanner having facilitated pointing - Google Patents

Abstract

The invention relates to a method for measuring by means of a three-dimensional measurement machine (1) comprising a measurement head (9) including a laser emitter (16) for emitting an incident laser beam toward the part to be measured, and an image sensor (17) for detecting a laser beam reflected by the part. The method includes a phase of positioning the measurement head relative to the part to be measured, comprising the following steps: supplying at least one indicator representing the position of the incident laser beam on the image sensor; moving the measurement head closer to or farther from the part to be measured depending on the indicator. The invention further relates to a three-dimensional measurement machine (1) for implementing said method.

Description

 Easy Point Scanner

The present invention relates to the field of coordinate metrology and more particularly to three-dimensional measurement arms.

 BACKGROUND OF THE INVENTION

 A three-dimensional measuring machine is a measuring instrument used in dimensional metrology whose function is to acquire the coordinates of different points of a part to be measured in order, for example, to verify the conformity of dimensions, geometry and / or forms of the room.

 Such machines generally comprise a base on which is mounted a measuring arm at the end of which is a measuring head. The measuring arm is conventionally constituted of rigid segments interconnected for example by means of pivots and / or ball joints provided with encoders accurately measuring the movements of the segments relative to each other.

The measuring head has means for acquiring a point on an object to be measured.

 There are two main types of measuring heads depending on whether the measurement is made by contact or without contact with the part.

 In the measuring heads by contact, the measuring head comprises a probe to come into contact with the part. The acquisition of the coordinates is controlled either automatically by detecting the contacting of the probe with the surface of the part or by the operator by means of a command button that the operator actuates when the probe is in contact with the zone. searched for the piece.

In non-contact measuring heads, the measuring head usually integrates a laser pointer diode which illuminates an area of the surface of the part to be measured and an optical sensor or camera which achieves an acquisition of the reflected light and deduces therefrom the distance measurement by calculating the phase difference between the incident light beam and the light beam which is reflected by the surface of the piece to be measured. Some measuring heads, called scanner heads, project a flat beam forming a line on the part to be measured to allow rapid acquisition of the shape of the part to be measured.

 The control of the acquisition can be carried out continuously or punctually by the operator by means of a control button that the operator actuates when the probe is in contact with the desired zone of the workpiece or when the dotted zone is illuminated. by the light signal. When controlling the acquisition, the relative positions of the different segments of the measuring arm are stored in the memory of a processing unit connected to the measuring arm. The processing unit is arranged to determine the coordinates of the measurement points in a repository, generally attached to the base, from the dimensions of the segments, their relative positions and the information of the measurement head. An adapted treatment of these coordinates makes it possible to extract dimensions, shape and geometry of the piece to be measured.

 The aim of the invention is to improve the performance of non - contact measuring head measuring machines.

 In such measuring machines, the performance of the measurement is related to the number of points that can be simultaneously acquired by the camera.

For reasons including optical, this ability to acquire a large number of points depends in particular on the respective positions of the camera and the piece to be measured. Indeed, the camera and the source of the laser beam have convergent optical axes in such a way that when the distance between the workpiece and the measuring head is within a predetermined distance range, the area of the workpiece illuminated by the laser beam is in the field of the camera. As a result, too close to or too far from the room, the camera does not see the area of the room illuminated and therefore does not allow the measurement to be made. Even within the range of distances in which the camera is able to acquire the measurement, there is an optimum measurement area corresponding to the simultaneous acquisition of a maximum number of points by the measuring device. In fact, the accuracy of the measurement reduces at the same time as the distance separating the measuring device from the part to be measured increases. On the other hand, the portion of light projected on the part and visible by the camera (and therefore the number of measuring points that can be acquired simultaneously) increases with the distance separating the piece to be measured from the measuring device. Thus, it is difficult for the user to position the measuring head so as to obtain a sufficiently accurate measurement of a sufficiently dense cloud of points.

 When a computer equipped with a screen is connected to the machine to be measured, the operator could consult the screen to see if the measuring head is positioned optimally with respect to the workpiece. Indeed, the computer can provide an alert message when the measurement could not be performed or the accuracy or the number of points acquired simultaneously is unsatisfactory. However, the operators can not generally have the screen and the room simultaneously in their field of vision so that they preferentially look at the part to be measured.

 OBJECT OF THE INVENTION

An object of the invention is to facilitate measuring operations carried out by a measuring head laser by limiting the complexity of the latter. SUMMARY OF THE INVENTION

 For this purpose, according to the invention, a measuring method is provided by means of a three-dimensional measuring machine comprising a measuring head comprising a laser transmitter for emitting a laser beam incident on the part to be measured and a sensor for measuring image to detect a laser beam reflected by the part. The method comprises the steps of:

 - analyzing an image provided by the image sensor to detect a position of the reflected laser beam on the image sensor;

 - providing at least one indicator representative of the position of the reflected laser beam on the image sensor;

 - Move the measuring head closer to or away from the workpiece according to the indicator.

 Thus, while taking the measurement of the part, it is possible to know simply if the measuring head is correctly positioned and if it is necessary to move it to position it optimally.

 Advantageously, the indicator is provided by the measuring head.

 When the measuring head is manipulated by an operator, the operator can have the part and the measuring head simultaneously in his field of vision. The indicator is therefore noticeable by the operator without the latter having to leave the room of the eyes.

 Preferably, different indicators are emitted depending on whether the measuring head must be near or away from the part to be measured.

 This further facilitates the correct positioning of the measuring head by the operator who is guided by the various indicators that he perceives.

The invention also relates to a machine for Three - dimensional measurement comprising a processing unit connected to a measuring head comprising a laser transmitter for transmitting to the part to be measured an incident laser beam and an image sensor for detecting a laser beam reflected by the part. The processing unit and the measuring head are arranged to implement the above method.

 BRIEF DESCRIPTION OF THE DRAWINGS

 Reference will be made to the appended figures among which:

 FIG 1 is a schematic perspective view of a measuring arm according to the invention;

 FIG 2 is a schematic perspective view partially broken away of a measuring head according to the invention;

 FIG. 3 is a logic diagram describing the operation of the measuring machine according to the invention.

 DETAILED DESCRIPTION OF THE INVENTION

Referring to Figure 1, the measuring machine according to the invention, here a generally designated articulated arm 1, comprises a fixed base 2 which is connected to a support such as a table or the floor and which carries a vertical shaft 3 on which is rotatably mounted a bearing 4. A first end of a first arm segment 5 is articulated on the bearing 4 by means of a pivot connection 6 of horizontal axis. The second end of the first arm segment 5 receives a second arm segment 7 articulated at this end about a pivot 8 along a horizontal axis. The other end of the second segment 7 of the measuring arm 1 receives a measuring head 9 also articulated along a pivot 10 of horizontal axis. The bearing 4 and the pivots 6, 8 and 10 are respectively provided with an absolute rotary encoder 11, 12, 13 and 14 measuring the respective angles of rotation of each of the joints of the measuring arm 1. With reference to FIG. 2, the measurement head 9 comprises a housing 15 provided with a laser diode 16, a CCD sensor 17 and a positioning indicator, in this case an RGB LED 19, all connected to an electronic card. 20. The laser diode 16 is mounted on the measuring head to emit a light beam in the form of a flat incident laser beam 18 extending on either side of an optical axis and the CCD sensor 17 is mounted below the laser diode 16 to have its optical axis inclined, for example at 30 °, with respect to the optical axis of the incident laser beam. The electronic card 20 comprises storage means 21 and a microcontroller 22 arranged to notably analyze the phase difference between the incident light beam emitted by the laser diode 16 and the reflected laser beam received by each of the elementary detectors (commonly called "pixels") of the CDD sensor 17 after reflection of the beam on the object to be measured. The microcontroller 22 is arranged to calculate then the distances separating the emission point of the laser (namely the laser diode 16) of the object to be measured.

 These distances as well as the values measured by the encoders 11 to 14 are transmitted to a processing unit 23 which then determines the coordinates of the measurement points in an Oxyz orthogonal reference linked to the fixed base 2. From the coordinates of several points, the processing unit 23 calculates the distances separating the measurement points and / or the geometry of the measured part.

The measuring head 9 makes it possible to acquire the measurement points situated in an acquisition zone 24 corresponding to the intersection of the incident flat laser beam 18, here of triangular shape, emitted by the laser diode 16 and the field of view. acquisition covered by the CCD sensor 17. This acquisition zone 24 corresponds to measuring points located at a distance from the laser diode 16 for example between 91.5 millimeters and 222 millimeters and located in the incident laser beam 18. This acquisition zone 24 is framed by two zones 25 and 26 extending respectively between 0 and 91.5 millimeters from the laser diode 16 and beyond 222 millimeters thereof, which correspond to zones in which the measurement is impossible. The acquisition zone 24 comprises a median zone 24.1 in which the measurement is optimal because, in this zone, the width of the beam makes it possible to acquire a large number of points with good precision (here, in the order of 0.1%). This optimal acquisition zone 24.1 is framed by a first secondary acquisition zone 24.2 and a second secondary acquisition zone 24.3. In the 24.2 zone closest to the laser diode 16, the accuracy of the measurement is good (less than 0.1%) but the beam width is small, resulting in the simultaneous acquisition of a small number of measurement points and therefore an extension of the acquisition times for a given part with respect to an acquisition in zone 24.2. In the zone 24.3 furthest away from the laser diode 16, the accuracy of the measurement is low (of the order of 0.3%) over a large number of measurement points which degrades the overall accuracy of the measurement of the room.

 In the embodiment described, the optimum acquisition area 24.1 extends from a distance of 120 millimeters from the laser diode 16 to a distance of 190 millimeters from the laser diode 16.

 Referring to Figures 2 and 3 the operation of the measuring head 9 is detailed.

When the user wishes to acquire the shape of a surface of a part to be measured - here the surface ABCD of a parallelepiped 30 - he orients the measuring head 9 towards the surface ABCD and puts the arm of measurement 1, which activates the measuring head 9 (step 30) and energizes the laser diode 16 which then emits an incident laser beam 18 (step 31) allowing the user to adjust the sight on the surface ABCD. At the same time, the CCD 17 receives the laser beam reflected by said surface and transmits an image signal to the microcontroller 21.

 The microcontroller 21 processes the information by analyzing the image signal (step 32) to determine the position of the reflected light beam on the CCD sensor 17. The CCD sensor 17 is virtually divided into three horizontal bands 17.1, 17.2, 17.3 respectively corresponding at the points of reflection of the points situated in the acquisition zones 24.1, 24.2, 24.3 of the acquisition zone 24. The microcontroller 21 then commands the LED 19 to display a color which is a function of the sensor band CCD 17 on which is reflected the greatest number of points by the reflected light beam (step 33).

 When the analysis of the image signal reveals that the elementary detectors of the central zone 17.2 of the CCD sensor 17 are mainly illuminated, the part is in the optimal distance range 24.1 and the microcontroller 21 controls the ignition of the diode 19 in the green color (step 35). The operator is then informed that he achieves optimal acquisition of the points of the part to be measured when scanning the ABCD surface with the incident laser beam.

When the analysis of the image signal reveals that the elementary detectors of the upper peripheral band 17.1 of the CCD sensor 17 are predominantly illuminated, the part is in the range of distance 24.2 and the microcontroller 21 controls the ignition of the diode 19 in the blue color (step 34). The operator is then informed that he is not in the zone optimal measurement of the measuring head 9 and it must then move the measuring head 9 of the room to continue the acquisition of the piece to be measured under optimal conditions.

 When the analysis of the image signal reveals that the elementary detectors of the lower peripheral band 17.3 of the CCD sensor 17 are mainly illuminated, the part is in the range of distance 24.3 and the microcontroller 21 controls the ignition of the diode 19 in the yellow color (step 36). The operator is then informed that he is not in the optimal measurement zone of the measuring head 9 and that he must then bring the measurement head 9 closer to the part to continue the acquisition of the part to measure under ideal conditions.

 When none of the areas of the CCD sensor 17 are illuminated, the measurement head is located in one of the zones 25 or 26 in which the acquisition is impossible and the microcontroller 21 then commands the LED 19 to display the the red color (step 37).

 This produces a laser measurement head 9 comprising a positioning indicator - the colored display of the LED 19 - which allows the operator to know if the measuring head 9 is at the right distance to the workpiece. This indicator also allows the user to adjust the position of the measuring head 9 so as to obtain an optimal measurement. Alternatively, the user can take a measurement when the measuring head is in the zones 24.2 and 24.3.

According to a particular embodiment, the luminous intensity of the RGB LED 19 is adjustable in order to adapt to the ambient lighting conditions by means of a mechanical control on the measuring head 9, for example a potentiometer, or means of a software command located in the processing unit 23, or again via a brightness sensor.

 According to another advantageous embodiment, the color of the indicator light provided by the RGB LED 19 includes a portion of blue, green and yellow whose respective intensities are proportional to the number of points in the areas 17.1, 17.2 and 17.3 of the CCD sensor 17.

 Of course, the invention is not limited to the embodiments described but encompasses any variant within the scope of the invention as defined by the claims.

 In particular,

 although here the efficiency indicator of the measuring head is, here, the colored display of an LED, the invention applies to other types of efficiency indicator such as an indicator comprising a sound signal or a vibration, or the frequency of a flashing light;

 - Although here the measuring head is articulated on the end of the measuring arm, it can also be rotatably mounted on the end of the measuring arm;

 although here the receiver for the reflected light is a CCD sensor, the invention is also applicable to other types of reflected light receiver such as for example a CMOS sensor;

 - Although here the acquisition area of the measuring head is between 25 millimeters and 235 millimeters of the laser diode, the invention also applies to measuring heads having a different acquisition area;

although here the surface of the CCD sensor is subdivided into a grid of three zones, the invention also applies to different number and disposition zones such as for example two zones, four or more four;

 - Although here the measuring arm rests on a fixed base, the invention also applies to a measuring arm linked to a mobile base;

 -Although here the analysis of the signal of the image received by the CCD sensor 17 and the generation of the indicator are carried out by the microcontroller 21, the invention also applies to an analysis of the signal of the image received and a generation of the indicator produced by the processing unit 23.

Claims

1. Measuring method by means of a three-dimensional measuring machine (1) having a measuring head (9) comprising a laser transmitter (16) for emitting an incident laser beam (18) to the piece to be measured and a sensor for measuring image (17) for detecting a laser beam reflected from the workpiece, the method comprising the steps of:  - analyzing an image provided by the image sensor to detect a position of the reflected laser beam on the image sensor (17);  providing at least one indicator (19) representative of the position of the reflected laser beam on the image sensor (17);  - Move the measurement head (9) closer to or away from the part to be measured according to the indicator (19), characterized in that the indicator (19) is provided by the measuring head (9).  The method of claim 1, wherein the indicator (19) is a visual indicator.  3. Method according to claim 1, wherein different indicators (19) are emitted according to whether the measuring head (9) is to be moved closer to or away from the piece to be measured.  The method of claim 3, wherein the indicator (19) is a colored visual indicator. 5. A three-dimensional measuring machine (1) comprising a processing unit connected to a measuring head (9) comprising a laser transmitter (16) for transmitting an incident laser beam (18) and an image sensor towards the part to be measured. (17) for detecting a laser beam reflected by the workpiece, characterized in that the processing unit (23) and / or the measuring head (9) are arranged to implement the method according to one of the any of the preceding claims and wherein the measuring head (9) is provided with at least one diode (19) forming the indicator.