moment sensor using FEM and its fabrication for an intelligent robot

Sensors and Actuators A 133 (2007) 27–34

Review

Design of a six-axis wrist force/moment sensor using FEM and its fabrication for an intelligent robot Gab-Soon Kim ERI, Department of Control and Instrumentation Engineering, Gyeongsang National University, 900 Gazwa-Dong, Jinju, Kyungnam 660-701, Republic of Korea Received 6 October 2005; received in revised form 17 March 2006; accepted 30 March 2006 Available online 11 May 2006

Abstract This paper describes the design of a six-axis force/moment sensor using FEM (finite element method) and its fabrication. In order to safely grasp an unknown object using an intelligent hand in robot, the hand has to perceive the weight of it. The weight is calculated by forces Fx , Fy , Fz measured from the six-axis wrist force/moment sensor attached to an intelligent robot’s hand. And, in order to accurately push and pull an object, forces and moments should be measured. Also, the position of the robot’s finger contacted on an object are calculated by forces Fx , Fy and Fz , and moments Mx , My and Mz measured from the six-axis wrist force/moment sensor. Therefore, an intelligent robot’s hand should get a six-axis wrist force/moment sensor that can measure forces Fx , Fy and Fz , and moments Mx , My and Mz simultaneously. The size of the six-axis force/moment sensor for an intelligent robot’ wrist is very important. If its diameter is larger or its thickness (length) is longer, it cannot be mounted in robot’s wrist or it will break down under the applied moment Mx or My . So, its size is similar to that of the wrist of human being, that is, the diameter is about 60–80 mm and the thickness (length) about 20–40 mm. But the manufactured sensors are not proper in size for the intelligent robot’s wrist. Thus, the six-axis force/moment sensor should be developed for the intelligent robot’s wrist. In this paper, the structure of a six-axis wrist force/moment sensor was modeled for an intelligent hand in robot newly. And the sensing elements of it were designed by using FEM and were fabricated by attaching strain-gages on the sensing elements. And, the characteristic test of the developed sensor was carried out. The rated outputs from FEM analysis agree well with the results from the experiments. The interference error of the sensor is less than 2.85%. © 2006 Elsevier B.V. All rights reserved. Keywords: Intelligent robot; Six-axis wrist force/moment sensor; Interference error; Rated output; Intelligent hand; Robot’s finger

Contents 1. 2. 3.

4. 5. 6.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Forces and moments in a robot’s wrist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design of a six-axis wrist force/moment sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. Structure of sensing elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2. Design of sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3. Strain analysis of sensing element . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Attachment position of strain-gages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fabrication of sensor, results and consideration of characteristic test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

E-mail address: [email protected]. 0924-4247/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.sna.2006.03.038

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G.-S. Kim / Sensors and Actuators A 133 (2007) 27–34

1. Introduction Scientists have been researching the development of an intelligent robot because people want to get a mechanism that can work for a human being. In order to get the similar hand’s function to a human, the six-axis wrist force/moment sensor that can measure forces Fx , Fy , Fz and moments Mx , My , Mz simultaneously is mounted to the hand of it [1–7]. The sensor is used to accurately measure the weight of an unknown object to grasp it safely, and to acquire three forces and three moments to push and pull it properly. Also, an intelligent robot needs to know the forces and moments for measuring from the center of the sensor to the position of an object, when an intelligent finger pushes it. Kim [8–17] developed some kind of multi-axis force/moment sensor with interference error of less than 3%, but they cannot be mounted to an intelligent robot because it is not proper in size. The sensing elements of the developed sensors have the disadvantage that is difficult to design the sensor with the various rated outputs and loads. The United States and Japan [18–20] have already developed and handled many kind of multi-axis force/torque sensor, but they are in high price and are not suitable to be mounted to a special intelligent robot’s hand. Thus, it is necessary to develop a six-axis wrist force/moment sensor with new structure for an intelligent robot’s hand. A sixaxis wrist force/moment sensor that is composed of Fx , Fy , Fz , Mx , My and Mz sensors should be designed and fabricated in a body to reduce interference error. And, it should have the proper rated load and the size, and the interference error of below 3% for an intelligent robot’s hand. In this paper, the new structure of a six-axis force/moment sensor is modeled for an intelligent robot’s hand, the sensing elements of it are designed using finite element method (FEM), and the sensor is fabricated by attaching strain-gages on the sensing elements. Also, the characteristic test of the developed sensor is performed with a special experimental setup. 2. Forces and moments in a robot’s wrist An intelligent robot’s hand is composed of a force sensor mounted to the finger, and a six-axis wrist force/moment sensor. When an intelligent robot’s hand grasps an unknown object, it should determine to safely grip the force of grasp-

ing direction by using values of three forces measured from the six-axis wrist force/moment sensor. And, the fingers safely grasp the object with the force value using force sensor. When an intelligent robot’s hand pushes and pulls an object, the position of finger and their forces can know by three forces and three moments measured from the six-axis wrist force/moment sensor. Fig. 1(a) and (b) show the shape that an intelligent robot’s hand with six-axis wrist force/moment sensor is gripping an unknown object and the hand (finger) is pushing it, respectively. When an intelligent robot’s hand pushes and pulls an ¯ unknown object, the force vector F¯ and moment vector Mcan be expressed as F¯ = Fx a¯ x + Fy a¯ y + Fz a¯ z = Fk a¯ k

(1)

¯ = Mx a¯ x + My a¯ y + Mz a¯ z M

(2)

where, Fx , Fy and Fz are the applied force along the x-, y- and z-direction, and Mx , My and Mz are the applied moment along the x, y and z-direction, respectively. The weight of an unknown object can be calculated as  F = mg = Fx2 + Fy2 + Fz2 (3) where, m is the mass of an object and g the local acceleration of gravity. In case of pushing an unknown object, the position from the centerline of z-direction of an intelligent hand to its finger can be written as ¯l = lx a¯ x + ly a¯ y + lz a¯ z

(4)

where, lx , ly and lz are the length of x-, y-, z-direction from the center point (O) of a sensor to an object, these can be calculated by the below equations. ¯ = ¯l × F¯ = {¯ax (ly Fz − lz Fy ) + a¯ y (lz Fx − lx Fz ) M +¯az (lx Fy − ly Fx )}

(5)

Mx = ly Fz − lz Fy

(6a)

My = lz Fx − lx Fz

(6b)

Mz = lx Fy − ly Fx

(6c)

Fig. 1. Six-axis wrist force/moment sensor mounted to intelligent robot.

G.-S. Kim / Sensors and Actuators A 133 (2007) 27–34

3. Design of a six-axis wrist force/moment sensor 3.1. Structure of sensing elements The structure of sensing elements for a six-axis wrist force/moment sensor should be modeled to get the interference error of 0%, when forces Fx , Fy and Fz , and moments Mx , My and Mz are applied to it. Thus, in this paper, the structure of the six-axis wrist force/moment sensor was modeled as shown in Fig. 2. The sensor is composed of a fixture ring, a force/moment transmitting block, fixture blocks FB1 ∼4, moving blocks MB1 ∼4, parallel-plate beams PPB1 ∼8, rectangular beams 1–4. The size of a rectangular beam with width d, thickness h and length l, and of a parallel-plate beam width b1 , thickness h1 and length l1 , and the gap between two plate beams are used as design variables for designing of the sensor. Parallel-plate beams (PPBs) are used for lower deflection of the sensor due to bending moment and lower twist due to twist moment from the applied force/moment to sensor. The transmitting block of the applied force/moment located the center of sensor and four rectangular beams that senses three forces and three moments were mounted with cross-shaped, and the other ends of beams were connected with moving blocks MB1 ∼4. The ends of one side of PPB1 and PPB2, PPB3 and PPB4, PPB5 and PPB6, PPB7 and PPB8 were attached to moving blocks MB2, MB4, MB1 and MB3, respectively, the other side of them was mounted to fixture blocks FB1, FB2, FB3 and FB4. And

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fixture blocks were fixed to a fixture ring. That is, the six-axis wrist force/moment sensor can get a function as a fixture ring and fixture blocks were fixed, and all PPBs, moving blocks, rectangular beams and a force/moment transmitting block were separated from each other. If force Fx is applied to the force/moment transmitting block, the bending strains on the rectangular beam 3 and 4, and the PPB5 ∼8 are larger than those on other beams and PPBs. In case of that Fy applied, the bending strains on the rectangular beam 1 and 2, and the PPB1 ∼4 are larger than those on other beams and PPBs. In case of that Fz is applied, the bending strains on the rectangular beam 1 and 4 are larger than those on other beams and PPBs. And, in case of that Mx is applied, the bending strains on the rectangular beam 1 and 2 are larger; in case of that My is applied, the bending strains on the rectangular beam 3 and 4 are larger; and in case of that Mz is applied, the bending strains on the rectangular beam 1 and 4 are larger than those on other beams and PPBs. Thus, the sensing elements to perceive force Fx are the surface of left and right of rectangular beam 3 and 4, that for force Fy are the surface of left and right of rectangular beam 1 and 2, that for force Fz are the surface of upper and lower of rectangular beam 3 and 4, that for moment Mx are the surface of upper and lower of rectangular beam 3 and 4, that for moment My are the surface of upper and lower of rectangular beam 1 and 2, and that for moment Mz are the surface of left and right of rectangular beam 3 and 4. The fixture ring of the six-axis wrist force/moment sensor is mounted to robot’s hand, and the force/moment transmitting block in center is fixed robot’s hand. Therefore, if forces and moments are applied to robot’s hand, they are transmitted to four rectangular beams through force/moment transmitting block. 3.2. Design of sensor

Fig. 2. Structure of sensing element for six-axis wrist force/moment sensor.

The design variables of the modeled six-axis wrist force/moment sensor are the size of body, the rated load and output of each sensor, the width b, the thickness h and the length h1 of rectangular beam, the width b1 , the thickness h1 and the length l1 of PPB, and the gap a between two parallel plates. Thus, in this paper, in the first place, the rated output of each sensor is determined by 0.5 mV/V (it is calculated from Eqs. (7) and (8)), the rated loads of Fx , Fy and Fz sensors are all 200 N, those of Mx sensor and My sensor are 2.5 N m, and that of Mz sensor is 5.0 N m. The diameter of a fixture ring is 100 mm, the size of rectangular-shaped consisted of PPBs is 74 mm, the height of the sensor 31 mm, the diameter of a force/moment transmitting block 30 mm, the attachment position of strain-gage 3 or 5 mm, and the rated strain is 250 ␮m/m. And, the length l of a rectangular beam and the length l1 of a PPB are determined by 14 mm in consideration of the size of the sensing elements and strain-gages to attach, and the sizes of width b, thickness h, width b1 , thickness h1 , gap a are determined by performing FEM software (ANSYS). Each sensor of the sixaxis wrist force/moment sensor is fabricated by attaching straingages on the sensing element of each sensor and composing of wheastone bridge using the attached strain-gages.

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G.-S. Kim / Sensors and Actuators A 133 (2007) 27–34

Fig. 3. Finite element mesh for FEM analysis of six-axis wrist force/moment sensor in three-dimension.

The rated output in the rated load is determined from the strain values of the attached strain-gages. Total strain of wheastone bridge can be calculated as following equation [12] ε = εT1 − εC1 + εT2 − εC2

(7)

where, ε is total strain from wheastone bridge, εT1 the strain of a tension strain-gage T1 , εC1 the strain of a compression straingage C1 , εT2 the strain of a tension strain-gage T2 , and εC2 the strain of a compression strain-gage C2 . And, the rated output can be calculated as below equation 1 Eo = Kε Ei 4

(8)

where, Ei is the input voltage of wheastone bridge, Eo the output voltage of wheastone bridge, K the factor of strain-gage (about 2.0), and ε the total strain got from Eq. (7). 3.3. Strain analysis of sensing element FEM software (ANSYS) was used to analyze the strain of the sensing element of the modeled six-axis wrist force/moment sensor. The strains on the sensing element of the selected rectangular beam must be lager than those of PPBs for lower interference error of the sensor. Fig. 3 shows the meshed shape of the structure of the sensor for analyzing FEM in three dimensions. In order to accurately analyze the sensing elements, the width b and thickness h of rectangular beam were divided into 4 and 6, the width b1 and thickness h1 of PPB were divided into 3 and 14, and the lengths l and l1 were divided into 1 mm unit. The strain analysis was performed by applying the rated load of each sensor to the force/moment transmitting block located upper part, after fixing four fixture blocks at x-, y- and z-direction. The strain at the attached position of strain-gage 3 and 5 mm from force/moment transmitting block is 250 ␮m/m. The FEM analysis was performed on the left and right surface of rectangular beam 3 and 4 for Fx sensor, the left and right surface of rectangular beam 1 and 2 for Fy sensor, the upper and lower surface of rectangular beam 3 and 4 for Fz sensor, the upper and lower surface of rectangular beam 3 and 4 for Mx sensor, the

Fig. 4. Deformed shape of six-axis wrist force/moment sensor under force Fx or Fy .

upper and lower surface of rectangular beam 1 and 2 for My sensor, and the left and right surface of rectangular beam 3 and 4 for Mz sensor. And, all PPBs were analyzed to compare the strain of rectangular beam with that of PPB at applied each load. The strain of rectangular beam should be larger than that of PPB for good sensor. The size of the rectangular beams and the PPBs was determined by performing FEM at several times. As a result, the width b, thickness h and length l of rectangular beam is 3.8, 4.6 and 14 mm, respectively, and the width b1 , thickness h1 , length l1 and gap of PPB is 1.3, 15, 14 and 5.4 mm, respectively. Figs. 4–7 show the deformed shape under the applied force Fx = Fy = Fz = 200 N, and moment Mx = My = 2.5 N m, Mz = 5.0 N m, respectively. The shape of the structure was symmetrically deformed on the basis of x-axis centerline and y-axis centerline like to be predicted. Fig. 8 shows the strains on each surface of rectangular beam 3 in case of (a) the right surface under the applied force Fx = 200 N; (b) the upper surface under the applied force Fz = 200 N; (c) the upper surface under the applied moment Mx = 25 N m; and (d) the left surface under the applied moment Mz = 5.0 N m. In Fig. 8, horizontal line is the length of rectangular beam, and vertical line is the strain on the centerline of beam. The strains are 0 ␮m/m at each point 7.5 mm in case of Fx , and 8.5 mm in case of Fz , Mx and Mz from force/moment transmitting block, respectively. It

Fig. 5. Deformed shape of six-axis wrist force/moment sensor under force Fz .

G.-S. Kim / Sensors and Actuators A 133 (2007) 27–34

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Fig. 6. Deformed shape of six-axis wrist force/moment sensor under moment Mx or My .

Fig. 9. Strain distributions on the inside and outside surface of PPB5 under force Fx and moment Mz .

Fig. 7. Deformed shape of six-axis wrist force/moment sensor under moment Mz .

almost straightly increases up to 515, 415, 477 and 533 ␮m/m in case of Fx , Fz , Mx and Mz for force/moment transmitting block, and decreases up to −449, −240, −143 and −314 ␮m/m for the moving block MB4 on the basis of each point 7.5 mm in case of Fx , and 8.5 mm in case of Fz , Mx and Mz . Those the strains are not 0 ␮m/m at the half points of beam is that the moving block MB4 was slightly rotated on the basis of z-axis line under force

Fig. 8. Strain distributions on each surface of beam 3 under forces and moments.

Fx , x-axis line under force Fz , x-axis line under moment Mx and z-axis line under moment Mz , respectively. The errors at both end point of beam are large because of the numerical error of the used ANSYS software at the point of block and beam, the mesh size and so on. In case of Fx and Mx , the strain on left surface and lower surface of rectangular beam 3 are equal to that of right surface and upper surface, but they all get reverse sign. The strain of rectangular beam 4 is equal to that of beam 3, because they have a same size, and symmetry on the basis of x-axis. Thus, under force Fy = 200 N is applied and moment My = 2.5 N m is applied, the results of FEM analysis of rectangular beam 1 and 2 for Fy sensor and My sensor is equal to beam 3 and 4, respectively. And, in case of Fz and Mz , the strain on lower surface and right surface of rectangular beam 3 are equal to that of upper surface and left surface but they all get reverse sign, respectively. The strain of rectangular beam 4 is equal to that of beam 3 because they have same size and symmetry on the basis of x-axis. Fig. 9 shows the strains on the inside surface of inside beam and the outside surface of outside beam of PPB5 under (e) the applied force Fx = 200 N and (f) the applied moment Mz = 5.0 N m. The strains are 0 ␮m/m at the point 7.0 mm in case of Fx and 9.5 mm in case of Mz from force/moment transmitting block. It almost straightly increases up to 175 ␮m/m in case of Fx and 76 ␮m/m in case of Mz for the moving block MB1, and decreases up to −188 and 30 ␮m/m for the fixture block FB1 on the basis of the point 7.0 mm in case of Fx and 9.5 mm in case of Mz , respectively. The strains on the outside surface and inside surface of outside beam and inside beam of PPB5 are all same, but they get reverse sign. The strains of PPB6 ∼ 8 are equal to that of PPB5, because they have a same size, and symmetry on the basis of x- and y-axis. As a result of FEM analysis, the maximum strain on left and right surface of rectangular beam 1–4 is larger 2.7 and 6.2 times than that on inside and outside surface of PPB1 ∼ 8 under the applied force Fx (Fy ) and moment Mx (My ), respectively. Thus,

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G.-S. Kim / Sensors and Actuators A 133 (2007) 27–34

Fig. 11. Photograph of developed six-axis wrist force/moment sensor.

lated strains due to Eq. (7) at the attachment location of each strain-gage. The rated strain of Fx sensor or Fy sensor is all 1062 ␮m/m, that of Fz sensor is 1000 ␮m/m, that of Mx sensor or My sensor is all 1278 ␮m/m and that of Mz sensor is 1252 ␮m/m. 5. Fabrication of sensor, results and consideration of characteristic test

Fig. 10. Attachment location of strain-gages for each sensor.

the six-axis wrist force/moment sensor can be designed to get larger stiffness and lower deflection. 4. Attachment position of strain-gages Fig. 10 shows the attachment location of strain-gages for each sensor. The attachment location of strain-gages for Fx sensor is S1–S4, for Fy sensor S5–S8, for Fz sensor S9–S12, for Mx sensor S13–S16, for My sensor S17–S20 and for Mz sensor is S21–S24. The attachment location of strain-gages is 3 and 5 mm along to length-direction from the force/moment transmitting block, and the centerline at width-direction. It is determined to get the maximum rated strain and interference error of 0% in consideration of the size of the used strain-gage. Table 1 shows the strains from FEM analysis and the calcu-

A six-axis wrist force/moment sensor was fabricated by attaching strain-gages at their locations and constructing weastone-bridge of each sensor. The used strain-gage is N2A13-S1452-350 made in Micro-Measurement Company, its gage factor is 2.06 and size is 3 mm × 7.2 mm. The used bond is M-bond 200 made in Micro-Measurement Company. The photograph of the fabricated six-axis wrist force/moment sensor is shown in Fig. 11. Fig. 12 shows the experimental set up for the characteristic test of a six-axis wrist force/moment sensor. It is composed of an arm, weights, a body, a digital multi-meter (ADCANTEST, R6552) and a power supply (UNICORN, UP-100DT). The manufactured six-axis wrist force/moment sensor must be carried out the characteristic test by using the experimental set up to evaluate

Table 1 Strains in the attachment location of strain-gages for each sensor Strain (␮m/m)

Fx Fy Fz Mx My Mz

T1

C1

T2

C2

ε

188 188 194 371 371 381

−343 −343 −306 −268 −268 −245

188 188 194 371 371 381

−343 −343 −306 −268 −268 −245

1062 1062 1000 1278 1278 1252

Fig. 12. Experimental setup for developed six-axis wrist force/moment sensor.

G.-S. Kim / Sensors and Actuators A 133 (2007) 27–34 Table 2 Rated outputs from FEM analysis and characteristic test of each sensor Rated output (mV/V)

Fx Fy Fz Mx My Mz

FEM

Exp.

Error

0.546 0.546 0.515 0.658 0.658 0.645

0.535 0.531 0.543 0.629 0.635 0.622

−2.01 −2.75 5.44 −4.41 −3.50 −3.57

Table 3 Interference error of each sensor

developed sensor (φ74 × 25) is similar to that of an intelligent robot’s wrist, and the interference error of it also is similar to that of the existing sensor produced from the developed country. The interference error of the sensor from FEM analysis was 0%, and the error from characteristic test was 2.85%. And, it was confirmed that the rated output of the sensor was about 0.500 mV/V. Thus, it is thought that the developed six-axis wrist force/moment sensor can be used as a component of a special hand of an intelligent robot. And, the modeled structure of the sensor can be designed a six-axis wrist force/moment sensor with various sizes and rated loads.

References

Interference error(%)

Fx = 200 N Fy = 200 N Fz = 200 N Mx = 2.5 N m My = 2.5 N m Mz = 5.0 N m

33

Fx

Fy

Fz

Mx

My

Mz

– 0.23 −1.30 0.09 2.07 −2.30

0.96 – 0.24 −1.98 0.61 1.91

0.09 0.29 – −0.24 −0.65 0.08

0.36 2.56 1.82 – 0.16 0.82

−2.85 0.07 −1.63 0.06 – 0.23

2.07 0.54 0.81 −0.34 0.08 –

its rated output in the rated load. Each sensor was tested three times by using the experimental setup, and the output values from each sensor were averaged. Table 2 shows the rated outputs from the results of FEM analysis and characteristic test. The rated outputs from FEM analysis are the values calculated from Eq. (8), that for Fx , Fy , Fz , Mx , My and Mz sensors is 0.546, 0.546, 0.515, 0.658, 0.658 and 0.645 mV/V, respectively. The rated outputs from characteristic test of Fx , Fy , Fz , Mx , My and Mz sensors are 0.535, 0.531, 0.543, 0.629, 0.635 and 0.622 mV/V, respectively. If the result from the characteristic test is compared with that from FEM analysis, the error of the rated output of Fx sensor was −2.01%, of Fy sensor −2.75%, of Fz sensor 5.44%, of Mx sensor −4.41%, of My sensor −3.50% and of Mz sensor −3.57%. These errors are because of the numerical analysis error of FEM software, the attaching error of strain-gages, the machining error of the sensing element, and so on. To get the rated output of above 0.500 mV/V from FEM analysis in each sensor is designed with four rectangular beams in the same size. Thus, the structure of the sensor needs to design a rectangular beam-taped for the rated output of about 0.500 mV/V in each sensor. Table 3 shows the interference error of each sensor. The interference error of Fx sensor is −2.30%, of Fy sensor −1.98%, of Fz sensor −0.65%, of Mx sensor 2.56%, of My sensor −2.85% and of Mz sensor 2.07%. The maximum interference error of the developed six-axis wrist force/moment sensor was less than 2.85%. Therefore, it is thought that the sensor can be used for an intelligent robot’s hand. 6. Conclusions In this paper, the six-axis wrist force/moment sensor was newly developed for an intelligent robot’s hand. The size of the

[1] L. Zollo, et al., An experimental study on compliance control for a redundant personal robot arm, Rob. Autonomous Syst. 44 (2004) 101– 129. [2] S. Arimoto, Intelligent control of multi-fingered hands, Ann. Rev. Control 28 (2004) 75–85. [3] M.S. Lim, et al., A human-like real-time grasp synthesis method for humanoid robot hands, Rob. Autonomous Syst. 30 (2000) 261– 271. [4] C. Xiong, et al., Grasp capability analysis of multi-fingered robot hands, Rob. Autonomous Syst. 27 (1999) 211–224. [5] M. Ceccarelli, et al., Grasp forces in two-finger: modeling and measuring, in: Proceedings of Fifth International Workshop on Robotics in Alpe AdriaDanbube Region, 1996, pp. 321–326. [6] D. Castro, et al., Tactile force control feedback in parallel jaw gripper, in: Proceedings of the IEEE International Symposium on Industrial Electronics, vol. 3, V. 3, 1997, pp. 884–888. [7] S.T. Nkgatho, et al., Intelligent gripper using low cost industrial, in: Proceedings of the IEEE International Symposium on Industrial Electronics, vol. 2, V. 2, 1998, pp. 415–419. [8] G.-S. Kim, D.-I. Kang, S.-H. Rhee, K.-W. Um, Design and fabrication of a 3-component force/moment sensor using the plate-beams, Meas. Sci. Technol. 10 (1999) 295–301. [9] G.-S. Kim, D.-I. Kang, S.-H. Rhee, Design and fabrication of a 6-component force/moment sensor, Sens. Actuators 77 (1999) 209– 220. [10] G.-S. Kim, The development of a six-component force/moment sensor testing machine and evaluation of its uncertainty, Meas. Sci. Technol. 11 (2000) 1377–1382. [11] G.-S. Kim, The design of a six-component force/moment sensor and evaluation of its uncertainty, Meas. Sci. Technol. 12 (2001) 1445–1455. [12] G.-S. Kim, Design of 3-component sensor with force/moment ratio of wide range, KSPE 18 (2) (2001) 214–221. [13] G.-S. Kim, Design of Two-Axis Force Sensor for Robot’s Finger, The Institute of Control, Automation and System Engineers, KOREA, vol. 3, No. 1, 2001, pp. 66–70. [14] G.-S. Kim, Design of a robots hand with two 3-axis force sensor for grasping an unknown object, Int. J. Precision Eng. Manuf. 4 (3) (2003) 12–19. [15] G.-S. Kim, H.-D. Lee, Development of a six-axis force/moment sensor and its control system for an intelligent robot’s gripper, Meas. Sci. Technol. 14 (2003) 1265–1274. [16] G.-S. Kim, Development of a small 6-axis force/moment sensor for robot’s fingers, Meas. Sci. Technol. 15 (2004) 2233–2238. [17] G.-S. Kim, J.-J. Park, Development of the 6-axis force/moment sensor for an intelligent robot’s gripper, Sens. Actuators 118 (2005) 127–134. [18] ATI Industrial Automation, Multi-Axis Forcr/Torque Sensor, ATI Industrial Automation, 2005, pp. 4–45. [19] BL Autotec, BL Sensor, Multi-axis force/torque sensor (BL-FTS-E020), BL Autotec, 2003, pp. 5–50. [20] Nisso Electric Works Co., Ltd, Multi Component Loadcell, Nisso Electric Works Co., Ltd, 1999, pp. 5–32.

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Biography Gab-Soon Kim got B.S. degree in Precision Mechanical Engineering from Jeonbook National University; M.S. and Ph.D. degrees in Precision Mechanical Engineering from Hanyang University, Republic of Korea, in 1986, 1990 and 1999, respectively. He was a senior researcher at Department of Force Laboratory, Korea Research Institute of Standards and Science, Republic of Korea,

from February 1990 to February 2000, and a visiting research at Department of Intelligent Robot Laboratory, University of Tsukuba, Japan, from July 2003 to June 2004. Since 2000, he has been with Gyeongsang National University, where he is currently Associate Professor at Department of Control and Instrumentation Engineering. His main research interests are in the areas of multi-axis force/moment sensor of intelligent robot, intelligent service robot and intelligent system.