Abstract:
The present disclosure relates to a drilling robot and a method for controlling a drilling robot including a driven mechanical structure allowing to place a drilling tool in a sequence of drillings programmed in terms of position and orientation of the drilling of a part such as a technical skin. The method includes a step of determining the acceleration of the drilling tool at the end of the approach on a drilling position, then also testing a stabilization condition of the drilling tool to finally establish a drilling authorization.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/FR2013/052988, filed on Dec. 6, 2013, which claims the benefit of FR 12/61766, filed on Dec. 7, 2012. The disclosures of the above applications are incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to a method for controlling a drilling robot. It also relates to a drilling robot to implement the method. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     In the state of the art, drilling robots which allow in particular to realize drilling series using drills, are already programmed. The drilling tool is mounted at the end of an articulated arm, for example with six degrees of freedom. Each axis is equipped with an actuator which allows to move the end of the arm in a determined position and orientation. The result is that the drilling tool can be approached according to a determined orientation in each programmed position of a sequence of drillings executed according to a determined program. 
     Thus, in response to the drilling program which is registered and executed on the controlling device of the driller robot, the drilling tool secured to the end of the robot arm undergoes a positive acceleration, then a negative acceleration (braking) during the approach of the following drilling position. When the drilling tool is finally stopped, an unsteady state may be established, the tool starting to oscillate around the reached drilling position. This instability depends on various factors comprising the approach acceleration, the inertia of the robot arm and others. 
     If the drilling was controlled upon detection of the end stop, the drilling would be entirely defective, with a non-cylindrical form and an ovalized section. 
     To overcome this drawback, it is known to count an inhibition period of the drilling to be counted from the stop detection on a drilling position so as to guarantee that the inertias and other braking forces of the unstable oscillations have absorbed the instability. The longest natural stabilization period provided in all programmed movements is chosen to realize the drilling program. 
     In an exemplary form, the drilling inhibition period was established at 2.5 sec. 
     But it was found that for all programmed positions, if no stabilization period is not longer by definition, an important number of stabilization periods were shorter than the retained inhibition duration. There is therefore a waste of time during the execution of the drilling program. 
     Furthermore, it was found that, during the drilling execution, because of many parameters, comprising the material irregularity of the part to be drilled, balancing or wear defects of the perforating drill and others, an unsteady state could still appear on the drilling tool. Among the drawbacks of these instabilities, the ovalization and the delamination problem(s) can be cited. 
     SUMMARY 
     The present disclosure reduces the duration of the complete execution of the drilling program by controlling the stability of the drilling tool so as to reduce to the strictly necessary the inhibition period before each drilling. The present disclosure also reduces the negative effects of instability at the stop of the drilling tool. 
     The present disclosure relates to a method for controlling a drilling robot. The drilling robot is of the type including a driven mechanical structure allowing to place a drilling tool in a drilling sequence programmed in terms of position and orientation of the drilling of a part such as a technical skin. 
     The present disclosure is characterized in that the method includes a step of determining the acceleration of the drilling tool at the end of the approach on a drilling position. When a stabilization condition of the drilling tool is established, a drilling authorization is generated. 
     According to other features, the present disclosure relates also to: 
     The logical condition of stabilization comprises the consideration of the instantaneous measurements of at least one component of the acceleration vector; 
     The test of the logical condition of stabilization includes the comparison of at least one value of the instantaneous measurements of at least one component of the acceleration vector at a predetermined threshold value; 
     The test of a stabilization condition of the drilling tool is combined with the progress of a pre-programmed period; 
     the step of determining the acceleration of the drilling tool at the end of the approach on a drilling position is continued after the drilling authorization so as to realize an analysis of the measurement data of the accelerometer, then to exploit the analysis data in real time in order to trigger on the drilling robot and/or on the drilling tool a corrective action such as a drilling cycle stop, or offline by realizing a measurement data file of the measured acceleration associated with each drilling position so as to provide traceability means of the drilling operation with reference to each programmed drilling position. One of the accelerometer measured components is established according to the axis of the perforating drill and in that the measurement of the components according to the two other components of the acceleration vector are tested in a logical condition of drilling quality to detect an ovalization of the programmed drilling. 
     The logical condition of the drilling quality comprises the comparison of components of the measured acceleration to a limit acceleration table. 
     The present disclosure also relates to a drilling robot implementing the drilling controlling method of the present disclosure. It includes an accelerometer secured to the end of a mobilization structure of a drilling tool, the accelerometer being connected to measurement, monitoring and testing means of a logical condition of stabilization on a sequence of drilling positions preprogrammed in a memory associated with a control calculator of the drilling robot. 
     According to other features: 
     the accelerometer is secured to the end of a mobilization structure of a drilling tool so that a measured acceleration component is aligned with the axis of a perforating drill; 
     The drilling robot includes a means for registering the drilling quality data, produced on the basis of the comparison of measurement data of the accelerometer at a table of comparison values, in a drilling traceability file in association with the drilling position. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which: 
         FIG. 1  is a diagram of a drilling robot adapted to implement the method of the present disclosure; 
         FIG. 2  is a timing diagram of signals generated during the controlling method in one form of the present disclosure; 
         FIG. 3  is a timing diagram of signals generated during the controlling method in another form of the present disclosure; 
         FIG. 4  is a block diagram of a controlling device of a driller robot of one form of the present disclosure; 
         FIG. 5  is a block diagram of a variant of a portion of the controlling device of a driller robot of the form of  FIG. 4 ; 
         FIG. 6  is a diagram for explaining another form of the method of the present disclosure; 
         FIG. 7  is a timing diagram of signals generated during the controlling method in another form of the present disclosure; and 
         FIG. 8  is a block diagram of a controlling device of a driller robot of another form of the present disclosure. 
     
    
    
     The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
       FIG. 1  represents a drilling robot which includes a mobile structure, one end  7  of which carries a drilling tool  12  on which a perforating drill  13  is mounted. The drilling head  12  may also carry more perforating drills  13 . Preferably, the mobile structure is composed of many articulated arms  4 - 7  one end of which is fixed in  3 . 
     The movements of the articulated arm end  4 - 7  are executed using actuators controlled by a computer  10  connected to the robot itself by a link  8 . The computer  10  executes a drilling program pre-established and registered in a memory of programs  9  associated with the calculator  10 . The drilling program allows to move the drilling tool on a determined series of drilling points or positions  14 - 16  on a part to be drilled  1 , such as a technical skin. 
     In  FIG. 2 , a timing diagram of signals generated during the controlling method in an form of the present disclosure is represented. According to the method of the present disclosure, when the drilling program determines a stop (signal (a)— FIG. 2 ) of the end movement of the mobile structure  4 - 7  of the robot because a new drilling position has been reached, there is executed a step of determining the acceleration of the drilling tool at the end of the approach on a drilling position (signal (b)— FIG. 2 ) which takes a variable duration T counted from the stop date t 0  of the robot. When a stability condition of the drilling tool is established (date t 1 ), a drilling authorization is generated (signal (c)— FIG. 2 ). 
     In order to execute the step of determining the acceleration of the drilling tool at the end of the approach on a drilling position, an accelerometer  17  is disposed on the end  7  of the mobile structure  4 - 7  of the drilling robot. In one form, an accelerometer is used producing a three-dimensional measurement. In another form, one of the acceleration measurement directions is aligned with a reference direction of the drilling tool  12 . The axis of the perforating drill  13  may be chosen. 
     During the detection step of a stability condition of the drilling tool on the drilling robot, a test of a predetermined logical condition CL is executed as a function of the measured values (Ax, Ay, Az) of the acceleration of the form:
 
CL( Ax,Ay,Az )
 
     which takes the true or false value. In an exemplary form, the predetermined logical condition CL calculates at each instant t after the date t 0  the largest absolute value of the three measurement signals (Ax, Ay, Az) according to the three measured directions of the reference trihedron of the space 3D of the accelerometer. Then it compares this value to a threshold value Sa. The predetermined logical condition CL is therefore of the form:
 
CL=(max(| Ax|,|Ay|,|Az |)&lt; Sa )
 
     When the logical stabilization condition CL is not verified, the acceleration measurement is resumed and a new test of the stability condition CL is resumed on the basis of the new acceleration measurement. 
     It is noted that the accelerometer is in practice realized on the basis of a sensor, the acceleration sensitivity of which is maximum in a privileged direction and decreases more or less strongly when one deviates from this privileged direction. To improve the overall sensitivity of the accelerometer, to measure a component Ax, Ay or Az of the acceleration vector according to each of the three directions x, y, z of the reference trihedron of the space 3D, many sensors, each having a privileged direction of better sensitivity are associated in the accelerometer to produce each of the three components Ax Ay, Az of the acceleration vector with an improved sensitivity. 
     When the logical condition of stabilization CL is verified, the signal (b) ( FIG. 2 ) falls at the time t 1 , after a variable duration T of stabilization of the mobile structure of the drilling robot. This signal (b) fall produces (signal (c)— FIG. 2 ) an activation of an authorization signal of the drilling operation, the perforating drill  13  of the drilling tool starts rotating and takes a forward movement along its rotation axis, executes the drilling in the programmed position on the part  1 . This drilling axis defines an axis W constituting a 7th axis of the robot. We are therefore provided with enhanced stability of the drilling tool  12  and in a variable time T which is almost always inferior to the blocked stabilization period blindly applied in the state of the art. This results in a reduction of the complete duration of the drilling cycle and therefore an improvement of the productivity of the drilling robot. 
     In  FIG. 3 , a timing diagram executed in another form of the controlling method of the present disclosure is represented. The timing diagram of  FIG. 3  differs from that of  FIG. 2  in that a clock (signal (b)— FIG. 3 ), triggered at date t 0  determined by the end of the approach movement executed by the mobile structure of the robot (signal (a)— FIG. 3 ) places a determined period T allowing to interrupt the test of the logical condition CL of stabilization (signal (c)— FIG. 3 ) described in the form of  FIG. 2 . 
     Indeed, the stabilization condition of the end of the mobile structure which carries the drilling tool  12  ( FIG. 1 ) is verified at a date t 1  of authorization of the drilling operation (signal (d)— FIG. 3 ) which can be late (arrow  21 ) or early (arrow  20 ) according to the circumstances of the approach movement of the drilling tool  12 . If the establishment of the stabilization condition CL takes a too long time T, determined by the clock (signal (b)— FIG. 3 ), the test of the logical stabilization condition of the end of the mobile structure of the drilling robot is interrupted and the activation signal of the drilling operation (signal (d)— FIG. 3 ) passes to the high state and the drilling begins. 
     Thus the waste of time caused by a detection condition of an acceleration superior to the threshold of the logical condition CL that would not be produced by a stabilization defect of the end of the mobile structure of the drilling robot. 
     In  FIG. 4 , in block diagram form, an implementation of the controlling method described using the  FIG. 2  is represented. The blocks represented may be realized under various material realizations in the calculator  10  of the drilling robot, including electronic circuits or a micro-programmed microcontrollers programming. 
     An accelerometer  25  is mounted as the accelerometer  17  of the drilling robot  2 - 13  of  FIG. 1 . Its measurement signals are transmitted to a signal shaper  26  and the shaped measurement signals of the instantaneous acceleration are transmitted to a calculator  27  of a logical condition CL, defined above using  FIG. 2 . 
     The calculator  27  receives a signal, such as the signal (a),  FIG. 2 , or  FIG. 3 , of a circuit  28  for controlling the advance of the end of the drilling robot carrier of the drilling tool  12 . 
     When the stabilization condition CL is verified by the stability calculator  27 , a signal such as the signal (c)  FIG. 2  of drilling authorization is transmitted to a drilling controlling circuit  29 . 
     In  FIG. 5 , in a block diagram form, an implementation of the controlling method described using  FIG. 4  is represented. The implementation of this second form resumes the blocks of the form but interposes the block of  FIG. 5  between the blocks  27  and  28  of  FIG. 4 . 
     A register T  30  receives, by programming  30   a , a limit value T of test of the stabilization condition CL tested in the block  27  of  FIG. 4 . The value T is transmitted to a first input of a clock or time counter  31 , a second input  28   a  of which receives the detection signal of the end of the approach produced by the aforementioned advance controlling circuit  28  (signal (a)— FIG. 3 ). The counting of the duration T preprogrammed in the register T  30  is executed by the clock  31 , the output of which (signal (b)— FIG. 3 ) falls to the end of the period T at t 2 . 
     The period signals T coming from the clock  31  and of logical condition CL of stabilization coming from the stabilization calculator  27  are provided at the inputs of a logical gate OR  32  which produces an output  27   b  of drilling authorization such as the signal (d)  FIG. 3  at the activation input of the drilling controlling circuit  29  of  FIG. 4 . 
     In a third form of the controlling method of the present disclosure, the monitoring of the instantaneous measurement of the acceleration is continued during the drilling. The measurement data of the accelerometer are therefore analyzed in amplitude over time, by frequencies (transformed in Fourier) or still by time-frequency (transformed in wavelets). The result data of the analysis are therefore used in real time to trigger on the drilling robot and/or on the drilling tool a corrective action as a stop cycle of the drilling operation, or offline by realizing a measurement data file of the measured acceleration associated with each drilling position so as to provide traceability means of the drilling operation with reference to each programmed drilling position. The file is therefore registered at the control calculator  10  of the robot  2 - 13  for a subsequent exploitation in association with the drilled part  1 , the drilling tool  12  and the drill  13 , and the program  9  of the programmed drilling positions  14 - 16 . 
     In  FIG. 6 , a case of application of this third form of the controlling method of the present disclosure is represented. A drilling  23  is schematically represented in a preprogrammed drilling position in a reference xyz associated with the perforating drill, the X and Y axes being oriented in the plane of the figure and the Z axis on the normal to this plane along the axis of the drill. The ideal drilling  23  in the correct stabilization condition is of a perfectly circular section. Correct stability data associated with the position of drilling  23  can therefore be registered in a drilling traceability file. 
     If the stabilization condition is not correct during the drilling, the drilling is ovalized in  22  according to the axis X, with a dimension A superior to the diameter R of the circular section of the ideal drilling  23 . In this case, the acceleration measured along the axis X on the end of the mobile structure  4 - 7  of the drilling robot is not zero. These incorrect stability data are therefore registered in the drilling traceability file in association with the drilling position  23 . 
     The drilling program can determine a maximum ovalization rate O as the NR ratio of real drilling  22  to programmed drilling  23  should be respected. By registering limit acceleration tables SBX, SBY, in the X and Y directions, and a test execution of a logical condition of the drilling quality dependent on the acceleration measurement and on the limit acceleration data, it is provided to trigger a prohibiting action of the continuation of the drilling operation as soon as one of the components AX or AY measured on the accelerometer ( 17 ,  FIG. 1 ) exceeds the registered threshold limit SBX or SBY. 
     In  FIG. 7 , a timing diagram of controlling signals of this third form of the controlling method of the present disclosure is represented. The signal (a) of  FIG. 7  represents a temporal evolution of the activation signal or of the drilling authorization in a preprogrammed drilling position. 
     The signal (b) of  FIG. 7  represents the evolution over time of the analysis of the measurement data of the accelerometer ( 17 ,  FIG. 1 ). In a first portion  33 , the stabilization condition CL was tested after the approach of the drilling tool according to the first or second forms of the controlling method of the present disclosure. When the test of the logical condition CL is favorable in  38 , the signal (a) switches in  34  to give the drilling authorization and the test of the stabilization condition CL is completed. Immediately after this instant t 3 , in a second portion  35  of the signal (b), the logical condition of the drilling quality described using the  FIG. 5  was tested. 
     If the logical condition of the drilling quality is correct, the corresponding data of good drilling quality are registered in the drilling traceability file in association with the drilling position  23 . 
     If the logical condition of the drilling quality is incorrect, the signal (a) of drilling authorization falls to date t 4  interrupting the drilling and the corresponding drilling defect data are registered in the drilling traceability file in association with the drilling position  23 . 
     In one form, the supervision of the accelerometer is in all cases continued beyond drilling stop date t 4  and extended till a date t 5  preprogrammed to supervise the withdrawal of the drill  13 . 
     In  FIG. 8 , a section of the calculator  10  of the drilling robot of the present disclosure is represented wherein the drilling method of the form described using  FIGS. 6 and 7  is executed. The accelerometer  40  (similar to the accelerometer  17  of  FIG. 1 ) is connected to a circuit  41  shaper of measurement signals of the instantaneous acceleration of the end of the mobile structure of the driller robot. By prior programming in  42   a  the registration of the limit acceleration tables SBX, SBY is realized, in the X and Y directions in a register  42 . 
     The data of the register  42  and of the shaper  41  are then tested in a test comparator  43  which implements the logical condition of the drilling quality described using  FIG. 7 . Depending on the logical condition, an action module  44  executes a registering of the drilling quality data in the drilling traceability file in association with the drilling position  23  and, as the case may be, a stop of the drilling is generated.