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Measurement and Testing of the Matrix Proximity Sensors
MEASUREMENT AND TESTING OF THE MATRIX PROXIMITY SENSORS DANIEL BIMAN and VLAOIHtR CRuct Dept of Automation and Measurement, Faculty of Mechanical Engineering, Slovak Technical University, Nam.Slobody 17, 812 31 Bratislav.l, SLOVAJ
Abstract. The paper deals with the proximity sensing in robotics. Characteristics of the capacitive ~atrix proximity sensor for a robot hand are shown, methods of proximity image processing are described and facilities, utilization and ~pplications of the sensor are presented. The main part of the paper deals with the testing of this sensor, and presents the testing methods, algorithms and equipment. Also some experimental results are preGented and discussed. Key Words. Matrix sensors, calibration.
robots, data processing, sensor testing and
maximum speed, accuracy and reliability. Simllltaneously, it is possible to obtain data necessary for an object recognition and identification. It is also assumed that for many applications the proximity sensors and imagers are mostly less expensive than visual sensors utilized for similar purpose.
1. INTRODUCTION The research on the intelligent sensor equipment of different autonomous machines leads towards the development of redundant and multisensory systems (Bergamasco, 1990; Raczkowsky, 1990). The integration information from various sensors allows to improve the relative precision of the robot positioning with respect to the environment and to increase the data reliability. Moreover, it allows to obtain additional data useful for the object and environment identification. An information being received from visual, force-torque, tactile, and proximity sensors has the substantial role in this case.
2, CAPACITIVE MATRIX PROXIMITY SENSORS
Development of proximity sensors and expansion of their applications h~ve began during a few last years only (Regtien, 1989). Nowadays, the changes of the proximity sensor constructions from simple ones, with binary output, to the more sophisticated 3-D sensors can be found. This development went similarly as with the tactile sensors towards the matrix tactile sensors during the last decade. The time delay of the development have caused that the signal processing, applications as well as testing procedures remained behind if compare with the other types of sensors and imagers.
Different types of proximity sensors and imagf'rs were presel1ted (Fiorio ~t al., 1989; Masuda, 1986; Nakajima 1986). It is possible to recognize their development from simple ones to the multi-terminal proximity sensors. The electro-optical and acoustic proximity sensors are utilized the most frequently for the working range from a few millimeters up to a few meters. The capacitive matrix proximity sensors are considered the most appropriate for sensing in a very closed space near the gripper (Mauer, 1989; Rhoades et al . , 1988). The information obtained from the proximity multi-point sensors is similar to the tactile image. But instead of the touch and force sensing, the distance represented by the capacitance between the sensing elements and the grounded conductive object is detected by the capacitive proximity matrix sensors.
Obviously, the proximity sensors in the contrary to the visual, tactile or force-torque sensors have an equivalent neither in the human hand nor in any other human organs. They complete the robot sensor system with a prediction element which can look for and detect objects, estimate their position and . orientation with respect to the gripper and which allows to follow the object surface without touching it. This information allows continual optimizing of the gripping process and achievement of its
The base of the sensor is the set of sensing elements of a suitable shnpe and topology. The matrix p'roximity sensors develnped at the authors' laboratory consist of an 8x8 array of square sensing elements with dimensions 1.9x1.9 mm and center-to-center distances 2,5 mm. The scanning of sensing elements is performed by electronics located inside of the sensor body. The elements are connected to the multiplexers by means of the x-y distribution of exciting and reading
60
wires. Dimensions of the 65x25x16 mm. Its arrangement in figure 1.
sensor are is outlined
6. Analysis of the object surface structure. It is possible to estimate the shape of the surface of the object and to recognize holes, gaps or bumps, etc. 7. Solution and supporting of some tasks of the object recognition.
4. TESTING OF THE MATRIX PROXIMITY SENSORS The proposal of matrix proximity sensor testing is joined with problems of the multisensorial information evaluation. At single sensors the output signal unambiguously describes the input value. However, the output data from the matrix sensor can be considered either as the data from individual elements, or as the )-0 proximity image which in the certain way rp-flects the shape and position of the object or its part. The needed information can be obtained by the appropriate signal processing. For example, in the simplest case of the object detection, data can be used from individual elements but also as the mean value of the whole image. Utilization of the arithmetic mean allows the more precision and reliable detection of the object presence.
Fig.l. Capacitive matrix proximity sensor
3. PROXIMITY IMAGE PROCESSING
Exactness of the obtained information depends on the accuracy of the measured data and the data processing algorithm. The results depends also on the object size, shape and other particulars. with regard to the above mentioned complexity, the testing of the proximity sensor and imagers is divided into:
The proximity image represents the transformed values of the instantaneous capacitance of individual elements. The image processing makes it possible to exploit the data usable for many robot activities. The first stage of proximity im~qe processing consists of the sensing and preprocessing procedu~es, i.e. multiplexing, AID converslon, filtering and uniformization. It can be solved utilizing a simple hardware, e.g. the sensorial microcomputer. Next stage, the fundamental tasks of data processing, can be hierarchically arranged to: 1. statistical analysis of the proximity image - that allows simple and quick detection of the presence and estimation of the shape and position of the object. 2. surface analysis of the image that examines a proximity image of the object in levels planparallel to the sensor and allows continual detection of edges and position estimation in a 2-D space, 3. space analysis of the image that investigates the proximity image of the object placed in a 3-D space.
1. Calibrating tests - that evaluate the measured data without previous processing. The goal is to obtain data necessary for the sensor calibration and determination of the basic parameters (a response characteristic, sensitivity, cross-talk, etc.). 2 . Algorithmic tests - that evaluate data obtained by the specific image processing. These tests can serve for determination of the overall accuracy and the performance evaluation of the proximity sensor system, and also for comparison of different algorithms. The sensor is able to examine objects with six oor. It allows too many possibilities of the testing procedures. Moreover, the measured data depends on the size of sensed object, particularly if the object size is small, comparable with the size of sensing elements. Consequently, each procedure of sensor testing is proposed for the specific type of the object, and mostly one or two:DOF.
Based on the information obtained in fundamental image processing phase, a lot of more sophisticated tasks can be solved, depending on the actual robot activity. The possibilities of the matrix proximity sensor utilization can be resumed as follows: 1. Detection of the presence of an object. 2. OptimiZation of the position of the gripper during a grasping process before the touch. 3. Speed control of the gripper jaws based on the distance measurement between the object and the sensor surface. 4. Determination of the accurate position of an objact grasped in the gripper for the following handling or assembly operation. S. Detection of a slip or the movement of the object in the gripper, based on the position, orientation or edge changes checking.
Testing egui~ The testing equipment makes possible to test and calibrate the matrix proximity sensors and to check the algorithms of the image processing. Mutual positioning of the sensor and object was achieved by the movement of the sensor in the x-y plane (w~th accuracy of 0.1 mm) and rotation around the z-axis (accuracy of 0.1 deg), and movement of the object in z-direction (with accuracy of 0.01 mm). For measurement and control a multifunctional card equipped with a 12-bits AID converter with +1- 2.5 V input range was used to serve as a sensor interface. For the sake of testing, the AID converter output as binary value 0 was used (1 bit - 1.221 mV).
61
The testing equipment and procedures, data storing and processing as well as evaluation of measured data i. fully controlled by the personal computer.
5. EXPERIMENTAL RESULTS Cl
........
5.1
~ration
c!,oo
te.t.
The calibration tests can be carried out by measurements dividod into three groups as follows: 1. ste~dy state measurements with unloaded and equable loaded sensing elements - that provide data necessary for the sensor uniformity setting up, concerning both the unloaded ~t8te and sensitivities of the individual sensing elements. 2. Response characteristics measurp.ment th~t allow to evaluate nomin~l and working range of individual elements and the whole sensor. 3. Measurements providing another characteristics of the sensor: crosstalk~, response time, drift, stability, signal-ta-noise ratio, stability, etc.
10
0 .01
0.1
10
z/mm Fig.2. Response characteristic of arithmetic mean
out~ut
values of the unloaded and e~~ab~e loaded sensing element" Based on experlmental data the following parameters of the sensor specimens were determined: - relative non-uniformity of unloaded sensor (58\), - non-uniformity of the sensor sensitivity
Cl 1000
'""-"I
...
o
100
(41\) •
The output values of the equable loaded sensor are in the Table 1. The sensor was uniformed in unloaded state. The maximum and minimum ,values are typed bold. The arithmetic mean of the image is 619 bits. Table 1
10
Outl2u t values of eqy!!bllL.!..Qaded ~
555 605 593 621 618 667 705 648
505 639 649 627 691 596 641 666
601 636 639 659 625 632 681 613
529 608 611 625 629 633 617 630
541 591 598 611 607 634 632 581
5~7
572 589 573 612 609 625 600
577 621 612 645 617 629 606 564
1+-------~~~~~~~~--~--~~ 0 ,1 0 .01 10
636 668 711 675 666 676 686 515
z/mm fig.3. Response characteristic of single element from the response characteristics the detection capability of the sensor, with respect to the testing object, can be determined. From arithmetic mean (see Fig . 2), regarding to the noise level the distance range of the object detecti~n is over 5 mm. For the single element sensing this distance r~nge is about J mm. The distance range depends on the Object size the larger object, the bigger detectio~ capability. A large object with face overlapping the whole sensing area (20x20 mm 2 ) can be detected in distance over 10 mm.
The noise level of the individual elements of th<;! uniformed sensor is about ± 2 bits and the uncertainty of the mean value is ± 0.2 bits. Resl20nse characteristics. The response characteristics were measured ill the direction of z-axis. The testing object, the metal circular rod with diameter of 8 mm, was placed in the middle of the sensing area, with the face parallel to the sensor surface. Two characteristics were evaluated: the arithmetic mean of the proximity image as a response to the object distance (shown in figure 2), and the output value of one elem~nt in 4-th column and 5-th row of the sensing matrix (shown in figure 3).
The response characteristic can be measured in x-y plane, too. Dependence of the output value of the. element in 4-th column and 5-th row of the sensing matrix ~n the position of the testing object if lt is moving in y-direction in the distance of 0.5 mm above the sensor is shown in the figure 4. An influence ~f a leakage capacities between the object and element can be found there, as well as the linear part of the characteristic provided that the testing object is moving just above the sensing element.
62
where Di1 is the output value of the sensing flement in column i (i e l, .. m) and row j (j- l, .. n), a c and b c are center-t~ center distances of the elements in matrix rows and columns, respectively.
=t ?OdY'"1 N~r-----~-,--li.--,,
The test is starting with the testing object in the middle of the sensor, where the zero initial positions of the object dY and computed values dT x and dT y are defined. Then the testing object, the circular rod as mentioned above, is moving, in the distance of 0.5 mm above the sensor surtace, across the matrix in y-direction in the range of dY trom -15 mm to 15 mm with steps of 0.5 mm. The error of the determination of the position (dTy-dY) is shown in figure 5. In the range of dY about ± 5 mm the measured error is minimum and the accuracy is better than ± 0.13 mm.
,,, ,,, ,
30
25 20
15 10
-5.DO
-2.50
2.50
O.DO
dY'/mm
Fig.4. Response characteristic in y-direction
The crosstalks . On testing, one element in t~miJd~--of the sensing m~trix was grounded. The output values of the image are in the Table 2. The maximum crosstalks between the adjoining elements are about 10 \ .
E
3 .0
'E - 2 .5 >:' 2.0
Y 1.5
?: '0
1.0
............"'-......"..:::.---.-
'-' 0.5
Table 2
The crosstalks
..,....-~
0 .0
....
-0.5 -1.0
-1 -1
0 0
2
1 1 4 8 3 4
2 1
2 2
3
2
9
14 0
2
1 3 2
15 16 22
23 16 17 13 13
10 23 92 1075 95 19 14
13
2 4 13 112
15 3 4 3
0 2 2 7 1 3 2 0
0
-1.5
2
-2 .0
1 -3 1 2 0 1
-2.5 -3.0 4.-.........TT"'.................~.............,~......,.~'"'P'T~""T~....,... . . . . ....., -10.0 -7~ -5.0 -2.5 0.0 2.5 5.0 7.5 10.0 12.5
dY/mm
Fig.5. Error of the position detection Edoe detection. Testing of the edge detection algorithm accur~cy (Biman, 1992) was performed with positioning in axis y. The object was positioned in the same way as at the former test . The position of the edge B4 in the 4-th column of matrix was examined. Position of the object edge is characterized by dY'=dV-r (r is radius of the object). The error of the detected edge described by dB4 B4-dV' as a response to the dY' is shown in figure 6 . If at least two sensing elements in the column are cover,d by the object then the error is less than 0.8 mm.
5.2 Algorithmic tests The scope and subject of algorithmic tests are determined by the methods of proximity image processing. It is possible to propose several algorithms for the same procedure of the image processing, the basic functions were mentioned above in the part 3. The tests are focused to the statistical analysis of proximity image and the edge detection. Defined subject and ways of testing make them possible to compare and evaluate the results.
~J
The centre of the object i~~~ Coordinates of the centre T~ and T c~n be calculated according to the f~llowing formulas:
-2.5
(1)
-5~10.0 -7~
-5.0
-2.5
0.0
2.5
5.0
7.5
10.0
dY'/mm Tv
(2)
Fig . 6. Error of detected edge in the x-y plane
63
Area of the Ob1ect. The area of the proximity image of the object can be computed from the detected edges. The example of detected edges, from the proximity image of the circular rod with diameter of 8 mm, is in the figure 7. In the figure the Aij describes the detected edges in the rows of the sensor, the S¥ is the area detected in the row directlon, and the b c is the center-to-center distance in the column direction. f,'
IJO~U
us III
tlD llD U7 . III
If the object moves in direction parallel to the sensor surface (along the y-axis), the corresponding dependence of the detected area is plotted in the figure 9.
5. CONCLUSION The paper introduces the capacitive matrix proximity sensors. It describes its utilization in the robot sensor system and deals with the basic problems of testing and calibration of the sensors. The testing procedures are submitted, described and verified, the results of experimental data processing are presented and discussed. The attention is paid to the sensor uniformity, the response characteristics corresponding to movement in both directions, the parallel and perpendicular to the sensor surface, the errors of the position, edge and face area determination.
lA"
......... ur
1.• 1.0 '.1
~
' .1
If,' -;:;;NUMERICAl EOO£ IMAGE
Fig. 7
GIIAPHICAl EDGE IMAGE
The edge images of the circular rod
As the position of the object ch~nges the detected area changes too. Two tests were done with the c~rcular rod with the face area of 50,2 mm • The figure 8 shows the detected area, if the object moves in the direction perpendicular to the _ sensor surface.
6. REFERENCES
...
Bergamasco,M. et al. (1990). Multi-Sensor Integration for Fine Manipulation. In: Highly Redundant Sensing in Robotic Systems. Publication, (Tou, J.T. and J.G.Balchen, Eds.), Vol.F58, pp.55-66. Springer - Verlag. Biman,D. and V. Chudy (1990). Matrix Capacitance Imaging Sensor of Robot Effector. In: Proc. of the I-st Int . Symp. on Measurement and Control in Robotics. pp. C.1.1 - C.1.6. Houston, Biman,D. (1991). Proximity Matrix Sensor Image Processing. In: Proc. of Symposium on Robot Control. pp. 519524. Pergamon Press. Vienna. Fiorillo,A.S. et al. (1989) . An Ultrasonic Range Sensor Array for Robotic Fingertip. Sensors and Actuators, 17, 103106. Mauer,G.F. (1989). An End-Effector Based Imaging Proximity Sensor. J. of Robotics Systems, 3, 301-316. Masuda,R. (1985). Multifunctional Optical Proximity Sensor Using Phase Modulation. In: Proc. of the '85 ICAR. pp .
E eo E
.......
,~
?;' Vl
!IO 4~
40 ~
JO 2~
20 15 10 ~
0 0 .0
0.2
0.4
0.8
0.8
1.0
1.2
1.4
z/mm
Fig.8. Detected area if object moves z-direction
The results of tests confirm that the resolution ftnd reliability can be considerably incre~sp.d by the appropriate data processing. The feasible accuracy of the object position determination makes it possible to utilize the capacitive matrix proximity sensor for different manipUlation and assembly operations in known or unstructured environment.
in
169-176, T0ktt0'
Nakajima, S. (1986): Ultrasonic Proximity Sensor for Profile Following Work by . Robot Manipulators. Trans. Soc. Instrum. and Control Engineering, 22, 567-573. Rhoades, L.J., D.Risko and R.L.Rosmick (1988). Capacitor array sensors tactile and proximity sensing and methods of use thereof. Patent USA No. 4766389. 23.8.1988. . Raczkowsky,J. and U.Rembold (1990). The Multisensory System of the K~MRO Robot. In: Highly Redundant Sensing in Robotic Systems. (Tou,J.T. ~nd J.G.Balchen, Eds.), pp. 45-54, Springer-Verlag . Regtien,P.r.L. (1989). Sensor system for robot control. Sensors and Actuators, 17,91-101.
(f)
40 ~
JO
25
20 I~
10 ~
__~~~
O~~~~~~~~~~~~~~~ -12.~ -'0.1) -1 . ~ -5.0 -2.5 0.0 2.5 5.0 1~
10.0
12.~
dY/mm
Fig.9. Detected area if object moves in y-direction
64
Abstract. The paper deals with the proximity sensing in robotics. Characteristics of the capacitive ~atrix proximity sensor for a robot hand are shown, methods of proximity image processing are described and facilities, utilization and ~pplications of the sensor are presented. The main part of the paper deals with the testing of this sensor, and presents the testing methods, algorithms and equipment. Also some experimental results are preGented and discussed. Key Words. Matrix sensors, calibration.
robots, data processing, sensor testing and
maximum speed, accuracy and reliability. Simllltaneously, it is possible to obtain data necessary for an object recognition and identification. It is also assumed that for many applications the proximity sensors and imagers are mostly less expensive than visual sensors utilized for similar purpose.
1. INTRODUCTION The research on the intelligent sensor equipment of different autonomous machines leads towards the development of redundant and multisensory systems (Bergamasco, 1990; Raczkowsky, 1990). The integration information from various sensors allows to improve the relative precision of the robot positioning with respect to the environment and to increase the data reliability. Moreover, it allows to obtain additional data useful for the object and environment identification. An information being received from visual, force-torque, tactile, and proximity sensors has the substantial role in this case.
2, CAPACITIVE MATRIX PROXIMITY SENSORS
Development of proximity sensors and expansion of their applications h~ve began during a few last years only (Regtien, 1989). Nowadays, the changes of the proximity sensor constructions from simple ones, with binary output, to the more sophisticated 3-D sensors can be found. This development went similarly as with the tactile sensors towards the matrix tactile sensors during the last decade. The time delay of the development have caused that the signal processing, applications as well as testing procedures remained behind if compare with the other types of sensors and imagers.
Different types of proximity sensors and imagf'rs were presel1ted (Fiorio ~t al., 1989; Masuda, 1986; Nakajima 1986). It is possible to recognize their development from simple ones to the multi-terminal proximity sensors. The electro-optical and acoustic proximity sensors are utilized the most frequently for the working range from a few millimeters up to a few meters. The capacitive matrix proximity sensors are considered the most appropriate for sensing in a very closed space near the gripper (Mauer, 1989; Rhoades et al . , 1988). The information obtained from the proximity multi-point sensors is similar to the tactile image. But instead of the touch and force sensing, the distance represented by the capacitance between the sensing elements and the grounded conductive object is detected by the capacitive proximity matrix sensors.
Obviously, the proximity sensors in the contrary to the visual, tactile or force-torque sensors have an equivalent neither in the human hand nor in any other human organs. They complete the robot sensor system with a prediction element which can look for and detect objects, estimate their position and . orientation with respect to the gripper and which allows to follow the object surface without touching it. This information allows continual optimizing of the gripping process and achievement of its
The base of the sensor is the set of sensing elements of a suitable shnpe and topology. The matrix p'roximity sensors develnped at the authors' laboratory consist of an 8x8 array of square sensing elements with dimensions 1.9x1.9 mm and center-to-center distances 2,5 mm. The scanning of sensing elements is performed by electronics located inside of the sensor body. The elements are connected to the multiplexers by means of the x-y distribution of exciting and reading
60
wires. Dimensions of the 65x25x16 mm. Its arrangement in figure 1.
sensor are is outlined
6. Analysis of the object surface structure. It is possible to estimate the shape of the surface of the object and to recognize holes, gaps or bumps, etc. 7. Solution and supporting of some tasks of the object recognition.
4. TESTING OF THE MATRIX PROXIMITY SENSORS The proposal of matrix proximity sensor testing is joined with problems of the multisensorial information evaluation. At single sensors the output signal unambiguously describes the input value. However, the output data from the matrix sensor can be considered either as the data from individual elements, or as the )-0 proximity image which in the certain way rp-flects the shape and position of the object or its part. The needed information can be obtained by the appropriate signal processing. For example, in the simplest case of the object detection, data can be used from individual elements but also as the mean value of the whole image. Utilization of the arithmetic mean allows the more precision and reliable detection of the object presence.
Fig.l. Capacitive matrix proximity sensor
3. PROXIMITY IMAGE PROCESSING
Exactness of the obtained information depends on the accuracy of the measured data and the data processing algorithm. The results depends also on the object size, shape and other particulars. with regard to the above mentioned complexity, the testing of the proximity sensor and imagers is divided into:
The proximity image represents the transformed values of the instantaneous capacitance of individual elements. The image processing makes it possible to exploit the data usable for many robot activities. The first stage of proximity im~qe processing consists of the sensing and preprocessing procedu~es, i.e. multiplexing, AID converslon, filtering and uniformization. It can be solved utilizing a simple hardware, e.g. the sensorial microcomputer. Next stage, the fundamental tasks of data processing, can be hierarchically arranged to: 1. statistical analysis of the proximity image - that allows simple and quick detection of the presence and estimation of the shape and position of the object. 2. surface analysis of the image that examines a proximity image of the object in levels planparallel to the sensor and allows continual detection of edges and position estimation in a 2-D space, 3. space analysis of the image that investigates the proximity image of the object placed in a 3-D space.
1. Calibrating tests - that evaluate the measured data without previous processing. The goal is to obtain data necessary for the sensor calibration and determination of the basic parameters (a response characteristic, sensitivity, cross-talk, etc.). 2 . Algorithmic tests - that evaluate data obtained by the specific image processing. These tests can serve for determination of the overall accuracy and the performance evaluation of the proximity sensor system, and also for comparison of different algorithms. The sensor is able to examine objects with six oor. It allows too many possibilities of the testing procedures. Moreover, the measured data depends on the size of sensed object, particularly if the object size is small, comparable with the size of sensing elements. Consequently, each procedure of sensor testing is proposed for the specific type of the object, and mostly one or two:DOF.
Based on the information obtained in fundamental image processing phase, a lot of more sophisticated tasks can be solved, depending on the actual robot activity. The possibilities of the matrix proximity sensor utilization can be resumed as follows: 1. Detection of the presence of an object. 2. OptimiZation of the position of the gripper during a grasping process before the touch. 3. Speed control of the gripper jaws based on the distance measurement between the object and the sensor surface. 4. Determination of the accurate position of an objact grasped in the gripper for the following handling or assembly operation. S. Detection of a slip or the movement of the object in the gripper, based on the position, orientation or edge changes checking.
Testing egui~ The testing equipment makes possible to test and calibrate the matrix proximity sensors and to check the algorithms of the image processing. Mutual positioning of the sensor and object was achieved by the movement of the sensor in the x-y plane (w~th accuracy of 0.1 mm) and rotation around the z-axis (accuracy of 0.1 deg), and movement of the object in z-direction (with accuracy of 0.01 mm). For measurement and control a multifunctional card equipped with a 12-bits AID converter with +1- 2.5 V input range was used to serve as a sensor interface. For the sake of testing, the AID converter output as binary value 0 was used (1 bit - 1.221 mV).
61
The testing equipment and procedures, data storing and processing as well as evaluation of measured data i. fully controlled by the personal computer.
5. EXPERIMENTAL RESULTS Cl
........
5.1
~ration
c!,oo
te.t.
The calibration tests can be carried out by measurements dividod into three groups as follows: 1. ste~dy state measurements with unloaded and equable loaded sensing elements - that provide data necessary for the sensor uniformity setting up, concerning both the unloaded ~t8te and sensitivities of the individual sensing elements. 2. Response characteristics measurp.ment th~t allow to evaluate nomin~l and working range of individual elements and the whole sensor. 3. Measurements providing another characteristics of the sensor: crosstalk~, response time, drift, stability, signal-ta-noise ratio, stability, etc.
10
0 .01
0.1
10
z/mm Fig.2. Response characteristic of arithmetic mean
out~ut
values of the unloaded and e~~ab~e loaded sensing element" Based on experlmental data the following parameters of the sensor specimens were determined: - relative non-uniformity of unloaded sensor (58\), - non-uniformity of the sensor sensitivity
Cl 1000
'""-"I
...
o
100
(41\) •
The output values of the equable loaded sensor are in the Table 1. The sensor was uniformed in unloaded state. The maximum and minimum ,values are typed bold. The arithmetic mean of the image is 619 bits. Table 1
10
Outl2u t values of eqy!!bllL.!..Qaded ~
555 605 593 621 618 667 705 648
505 639 649 627 691 596 641 666
601 636 639 659 625 632 681 613
529 608 611 625 629 633 617 630
541 591 598 611 607 634 632 581
5~7
572 589 573 612 609 625 600
577 621 612 645 617 629 606 564
1+-------~~~~~~~~--~--~~ 0 ,1 0 .01 10
636 668 711 675 666 676 686 515
z/mm fig.3. Response characteristic of single element from the response characteristics the detection capability of the sensor, with respect to the testing object, can be determined. From arithmetic mean (see Fig . 2), regarding to the noise level the distance range of the object detecti~n is over 5 mm. For the single element sensing this distance r~nge is about J mm. The distance range depends on the Object size the larger object, the bigger detectio~ capability. A large object with face overlapping the whole sensing area (20x20 mm 2 ) can be detected in distance over 10 mm.
The noise level of the individual elements of th<;! uniformed sensor is about ± 2 bits and the uncertainty of the mean value is ± 0.2 bits. Resl20nse characteristics. The response characteristics were measured ill the direction of z-axis. The testing object, the metal circular rod with diameter of 8 mm, was placed in the middle of the sensing area, with the face parallel to the sensor surface. Two characteristics were evaluated: the arithmetic mean of the proximity image as a response to the object distance (shown in figure 2), and the output value of one elem~nt in 4-th column and 5-th row of the sensing matrix (shown in figure 3).
The response characteristic can be measured in x-y plane, too. Dependence of the output value of the. element in 4-th column and 5-th row of the sensing matrix ~n the position of the testing object if lt is moving in y-direction in the distance of 0.5 mm above the sensor is shown in the figure 4. An influence ~f a leakage capacities between the object and element can be found there, as well as the linear part of the characteristic provided that the testing object is moving just above the sensing element.
62
where Di1 is the output value of the sensing flement in column i (i e l, .. m) and row j (j- l, .. n), a c and b c are center-t~ center distances of the elements in matrix rows and columns, respectively.
=t ?OdY'"1 N~r-----~-,--li.--,,
The test is starting with the testing object in the middle of the sensor, where the zero initial positions of the object dY and computed values dT x and dT y are defined. Then the testing object, the circular rod as mentioned above, is moving, in the distance of 0.5 mm above the sensor surtace, across the matrix in y-direction in the range of dY trom -15 mm to 15 mm with steps of 0.5 mm. The error of the determination of the position (dTy-dY) is shown in figure 5. In the range of dY about ± 5 mm the measured error is minimum and the accuracy is better than ± 0.13 mm.
,,, ,,, ,
30
25 20
15 10
-5.DO
-2.50
2.50
O.DO
dY'/mm
Fig.4. Response characteristic in y-direction
The crosstalks . On testing, one element in t~miJd~--of the sensing m~trix was grounded. The output values of the image are in the Table 2. The maximum crosstalks between the adjoining elements are about 10 \ .
E
3 .0
'E - 2 .5 >:' 2.0
Y 1.5
?: '0
1.0
............"'-......"..:::.---.-
'-' 0.5
Table 2
The crosstalks
..,....-~
0 .0
....
-0.5 -1.0
-1 -1
0 0
2
1 1 4 8 3 4
2 1
2 2
3
2
9
14 0
2
1 3 2
15 16 22
23 16 17 13 13
10 23 92 1075 95 19 14
13
2 4 13 112
15 3 4 3
0 2 2 7 1 3 2 0
0
-1.5
2
-2 .0
1 -3 1 2 0 1
-2.5 -3.0 4.-.........TT"'.................~.............,~......,.~'"'P'T~""T~....,... . . . . ....., -10.0 -7~ -5.0 -2.5 0.0 2.5 5.0 7.5 10.0 12.5
dY/mm
Fig.5. Error of the position detection Edoe detection. Testing of the edge detection algorithm accur~cy (Biman, 1992) was performed with positioning in axis y. The object was positioned in the same way as at the former test . The position of the edge B4 in the 4-th column of matrix was examined. Position of the object edge is characterized by dY'=dV-r (r is radius of the object). The error of the detected edge described by dB4 B4-dV' as a response to the dY' is shown in figure 6 . If at least two sensing elements in the column are cover,d by the object then the error is less than 0.8 mm.
5.2 Algorithmic tests The scope and subject of algorithmic tests are determined by the methods of proximity image processing. It is possible to propose several algorithms for the same procedure of the image processing, the basic functions were mentioned above in the part 3. The tests are focused to the statistical analysis of proximity image and the edge detection. Defined subject and ways of testing make them possible to compare and evaluate the results.
~J
The centre of the object i~~~ Coordinates of the centre T~ and T c~n be calculated according to the f~llowing formulas:
-2.5
(1)
-5~10.0 -7~
-5.0
-2.5
0.0
2.5
5.0
7.5
10.0
dY'/mm Tv
(2)
Fig . 6. Error of detected edge in the x-y plane
63
Area of the Ob1ect. The area of the proximity image of the object can be computed from the detected edges. The example of detected edges, from the proximity image of the circular rod with diameter of 8 mm, is in the figure 7. In the figure the Aij describes the detected edges in the rows of the sensor, the S¥ is the area detected in the row directlon, and the b c is the center-to-center distance in the column direction. f,'
IJO~U
us III
tlD llD U7 . III
If the object moves in direction parallel to the sensor surface (along the y-axis), the corresponding dependence of the detected area is plotted in the figure 9.
5. CONCLUSION The paper introduces the capacitive matrix proximity sensors. It describes its utilization in the robot sensor system and deals with the basic problems of testing and calibration of the sensors. The testing procedures are submitted, described and verified, the results of experimental data processing are presented and discussed. The attention is paid to the sensor uniformity, the response characteristics corresponding to movement in both directions, the parallel and perpendicular to the sensor surface, the errors of the position, edge and face area determination.
lA"
......... ur
1.• 1.0 '.1
~
' .1
If,' -;:;;NUMERICAl EOO£ IMAGE
Fig. 7
GIIAPHICAl EDGE IMAGE
The edge images of the circular rod
As the position of the object ch~nges the detected area changes too. Two tests were done with the c~rcular rod with the face area of 50,2 mm • The figure 8 shows the detected area, if the object moves in the direction perpendicular to the _ sensor surface.
6. REFERENCES
...
Bergamasco,M. et al. (1990). Multi-Sensor Integration for Fine Manipulation. In: Highly Redundant Sensing in Robotic Systems. Publication, (Tou, J.T. and J.G.Balchen, Eds.), Vol.F58, pp.55-66. Springer - Verlag. Biman,D. and V. Chudy (1990). Matrix Capacitance Imaging Sensor of Robot Effector. In: Proc. of the I-st Int . Symp. on Measurement and Control in Robotics. pp. C.1.1 - C.1.6. Houston, Biman,D. (1991). Proximity Matrix Sensor Image Processing. In: Proc. of Symposium on Robot Control. pp. 519524. Pergamon Press. Vienna. Fiorillo,A.S. et al. (1989) . An Ultrasonic Range Sensor Array for Robotic Fingertip. Sensors and Actuators, 17, 103106. Mauer,G.F. (1989). An End-Effector Based Imaging Proximity Sensor. J. of Robotics Systems, 3, 301-316. Masuda,R. (1985). Multifunctional Optical Proximity Sensor Using Phase Modulation. In: Proc. of the '85 ICAR. pp .
E eo E
.......
,~
?;' Vl
!IO 4~
40 ~
JO 2~
20 15 10 ~
0 0 .0
0.2
0.4
0.8
0.8
1.0
1.2
1.4
z/mm
Fig.8. Detected area if object moves z-direction
The results of tests confirm that the resolution ftnd reliability can be considerably incre~sp.d by the appropriate data processing. The feasible accuracy of the object position determination makes it possible to utilize the capacitive matrix proximity sensor for different manipUlation and assembly operations in known or unstructured environment.
in
169-176, T0ktt0'
Nakajima, S. (1986): Ultrasonic Proximity Sensor for Profile Following Work by . Robot Manipulators. Trans. Soc. Instrum. and Control Engineering, 22, 567-573. Rhoades, L.J., D.Risko and R.L.Rosmick (1988). Capacitor array sensors tactile and proximity sensing and methods of use thereof. Patent USA No. 4766389. 23.8.1988. . Raczkowsky,J. and U.Rembold (1990). The Multisensory System of the K~MRO Robot. In: Highly Redundant Sensing in Robotic Systems. (Tou,J.T. ~nd J.G.Balchen, Eds.), pp. 45-54, Springer-Verlag . Regtien,P.r.L. (1989). Sensor system for robot control. Sensors and Actuators, 17,91-101.
(f)
40 ~
JO
25
20 I~
10 ~
__~~~
O~~~~~~~~~~~~~~~ -12.~ -'0.1) -1 . ~ -5.0 -2.5 0.0 2.5 5.0 1~
10.0
12.~
dY/mm
Fig.9. Detected area if object moves in y-direction
64