Optical Torque Sensors for Local Impedance Control
Realization of an Anthropomorphic Robot Arm
Dzmitry Tsetserukou, Riichiro Tadakuma, Hiroyuki Kajimoto and Susumu Tachi
The University of Tokyo
7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan.
Email: dima_teterukov@ipc.i.u-tokyo.ac.jp
We recently developed an optical torque sensor to replace
expensivestrain-gauge-based
sensorontheanthropomorphic robot arm and realize local impedancecontrol in individual joints.
Keywords: Optical torque sensor, Impedance control.

1. Introduction
Teleoperated slave robot developed for delicate tasks suchas interaction with users in remote environments ormanipulation of objects under hazardous conditions1) includes
anthropomorphic seven-degree-of-freedom (7-DOF) arms
(Fig. 1) with 8-DOF hands. Impedance control is used toachieve
stableenvironmental
interaction
andtorealize
controlled
dynamic
interaction
between a robot arm
and users. Impedancecontrol used in the armof the remote slave
robot
requiresmeasurementofexternal force exertedbyusers
duringinteraction. The force
6-axis force
imparted by users on
sensorstheanthropomorphic
arm is measured by a
6-axisforce/torquesensor (MINI 4/20, BL
AUTOTEC), marked
by rectangles in Fig. 1.
Even though therobotic system ensures
Fig. 1. Teleoperated slave robot.
safe interaction at theend-effector, other parts such as the shoulder and elbow may
cause injury during use because they do not have force
measurement sensors to limit the motor torque by feedback.
Direct sensing of applied torque through the DC motor circuit
is not acceptable due to low backdrive in harmonic drives withhigh gear ratio (=50). To realize user-friendly interaction of

any part of the anthropomorphic arm, we decided to use torquesensors at each joint to implement local impedance control,achieving virtual backdrive of transmission in each joint.
Commercial 6-axis strain-gauge-based force/torquesensors are used at the end-effector of a robot to monitor
assembly or machining. This application requires very highstiffness, but for users-robot interaction, high stiffness is not
the objective. Strain gauges have disadvantages of being
difficult to install and calibrate, easy to break, and having highelectrical noise sensitivity that makes them rather expensive.
We introduce an optical approach to detect torque anddiscuss the results of local impedance control on the basis ofdeveloped optical sensors to provide safety in user-robot
interaction.

2. Background
The torque transducer on the motor shaft includes a loadcell structure supporting the load and deflecting a known
amount in response to applied torque. Deformation of theelastic element is measured in different ways as follows:
1) Electrically2) Based on electromagnetic phenomena
3) Optically
These approaches include noncontact transducers
measuring relative displacement by light radiation detection,
Hall effect, Faraday’s law, and contacting transducers
measuring strain based on strain gauges, potentiometers,piezoelectric, and optical fibre.
2.1. Electrical Methods
Electrical measurement is associated essentially withstrain gauges and capacitive and piezoelectric sensing. Strain
gauge operation is based on variations in electrical resistancewith strain. When force is applied, strain changes the electricalresistance of gauges proportional to the load. Silicon
semiconductor strain gauges are often used due to highsensitivity. Strain in silicon causes its bulk resistance tochange, producing a signal 75 times stronger then conventional
foil gauges where resistance changes are only due todimensional changes in the resistor. Despite such benefits ofstrain gauges as high accuracy (linearity), about 0.03%-2.5%
of full scale (FS), high resolution of 1-3mV/V, their maximum
allowable strain is close to their breaking point. To guarantee

overload protection of transducers, mechanical stops limiting
deflections of flexures are necessary. Very stiff sensors may
only deflect a few ten-thousandths of a millimeter.
Manufacturing limit stops with such small clearances is very
difficult. Strain-gauge-based torque/force sensors are greatly
subjected to radial and other force components. Semiconductor
and foil gages require elaborate process for attachment by aspecialist. Another shortcoming of these sensors is their highsensitivity to electrical noise and temperature2).
Piezoelectric torque sensors are similar in operation tostrain gauges and based on the phenomenon in which a crystal
under the action of mechanical stress becomes electricallycharged. High stiffness and strength enable sensors to be
directly inserted into the torsion member. An example of thepiezoelectric effect is the invention3) where author exploitedchanges in the resonant frequency of the piezoelectric element
as a measure of the strain to which the torsion member issubjected. Extremely high accuracy (0.03% of full scale) andhigh signal output are their main advantages. Drawbacks
restricting their application are high cost and nonlinear output.
Many torque transducers are based on measuring therelative angle between the two ends of the torsion bar. This
principle was realized in the differential capacitive sensor formeasuring the relative angle4). The transducer is noncontact,robust, and compact. Two rotatable electrodes are placed
between two sensor plates. The relative angle between the tworotors and the absolute position of the rotor blades arecalculated from measurement of capacitive coupling between
different transmitting stator segment and a single receiving
electrode. Its drawback is high sensitivity to radialdisplacement and high cost. The relationship between thecapacitor capacity and permittivity of the dielectric material
between the capacitor plates also was used in patent5). In thisinvention, the apertured metal cage shielding a dielectric rotoris placed between capacitor plate rings fixed on opposite sides
of a torsion bar. The relative rotation of the apertured
conductive plates and the dielectric rotor changes the overall
differential capacitance of the system in proportion to torque.
2.2. Electromagnetic Phenomena
Faraday’s law (inductive sensors), magnetostriction, andmagnetoelastic effect are used in electromagnetic sensors. The
main advantage of linear variable differential transformers(LVDT) is their high degree of robustness, remarkable
resolution of about 0.1µm, good accuracy (0.01-0.3%), andeasier installation and calibration. High reliability is derived
from their operation principle based on magnetic transfer
eliminating physical contact across the sensing element. The
strong relationship between core position and output voltage of
secondary coils yields excellent resolution. Inductive sensors
suffer a reduction in signal at very low frequencies andaffected by electromagnetic noise. D. Vischer and O. Khatib
used this transducer in the torque sensor6). The hub-spoke
structure of this torque sensor is given in Fig. 2 (1 – flexible
beam, 2 – LVDT).

2

1

Fig. 2. Six-beam torque sensor with LVDT transducer6).
The smallest LVDT made by the Lucas Schaevitz XS-B
series weighs only 4.36 g and has an outer diameter of 4.77mm, but its length of 22.4 mm complicates compact overall
dimensions of the torque transducer.
The effect, in which applying stress to the materialcauses a change in its magnetization, is known as the Villarieffect or magnetostriction phenomena. Magnetostrictive torquesensors consist of rotational shaft, having a magnetostrictive
metal layer of a chevron configuration formed on the shaft, an
exiting coil, and a pickup coil for detecting the magnetic
property change of the magnetostrictive layer. When AC
current is applied to the exciting core, the magnetostrictive
layer is excited. Torque applied to the magnetostrictive
element generates stress. Permeability is changed by the Villarieffect and inductive output is generated in the pickup coil withtorsional load7). Advantages of the sensor are no physicalcontact between the shaft and housing, and high torsional
stiffness. Drawbacks are complicated manufacturing, bulky
heavy structure, need for a robust magnetic shield, andinsufficient performance (linearity – 3-5% FS, hysteresis 2-3%,
resolution 10 mV/V)8).
2.3. Optical Approaches
A light source, photosensor, and solid object modifying
the amount of light incident on the optical detector arenecessary to measure displacement between unmovable andflexible parts of the optical sensor. Photosensors have suchdrawbacks as nonlinearity and temperature sensitivity, but areconsiderably more reliable, cheap, and simplified in design. A
displacement is detected by interrupting light between sourceand detector, changing the intensity of reflected light, or the
relative movement of source and detector. S. Hirose and K.
Yoneda have significantly contributed to research on the
optical force/torque sensors [9, 10]. They proposed using a
split photosensor to detect displacement of the light source(LED) caused by applied force in two directions. This sensor isshown in Fig.3 (1 – force loaded adapter plate, 2 – load cell(elastic element), 3 – photodetector, 4 – LED, 5 – installation
adapter plate).

1
2
Y

5

76

Z
3

3. Development of Optical Torque Sensor

4
X

40

Fig. 3. Layout of the 6-axis optical force/torque sensor9).
As force applied to the plate 1, elastic solid body 2
deflects LED light incident on photosensor 3. Thus, magnitudeof photodetector output responds on exerting force/moment. In
cooperation with the Minebea Co. OPFT series of 6-axis
optical force/torque sensors was manufactured. Compared toconventional strain-gauge-based transducers, they are morecompact, lightweight, and cheap11), but they have complicatedcalibration due to nonlinear output, require application of DSP
for real-time computation of measured force, and have an
average accuracy of 5%.
At Nara Institute of Science and Technology, a 6-axis
optical force/torque sensor was developed for fMRI
application. The sensor was made from acrylic resin toeliminate any metal sensor components that generate fMRI
signal noise. The layout of the transducer12) is shown in Fig. 4.
Acceptance Optical Fiber
12
43
Photo Sensor

array of a radiation detector and two modulating apertured
disks placed between the source and detector. As torqueapplied to the shaft the relative position between disks alters
overlapping slots and hence the size of the apertures which
control the pattern of light incident upon the optical detector.
The 6-axis force/torque converter using LEDs and photodiodes
is given in reference15).

Emission Optical Fiber
Light BeamyxLight source
Elastic Frame

Fig. 4. Layout of the 6-axis optical force/torque sensor12).
The elastic frame has a Y-topology with S-shaped beams
to enable 6-DOF displacement of the sensing face. Forceexerted by users deflects the elastic frame, altering theintensity of light falling on optical fiber. The sensor provides
accuracy of 2.65% for measurement of moment MZ. The
transducer is complicated and intended only for narrow
applications.
The idea of the patent13) is calculating torque by
measuring the angle of twist of the torsion shaft throughdetection of differences in the rotation position of disks at
opposite sides of the torsion shaft using an optical encoder.
The encoder-type torque sensor suffers from large overall
dimensions and precise relative installation of apertured disks.
To overcome this, the author14) invented a torque sensor
including a source of optical radiation, a two-dimensional

3.1. Specifications
Above-mentioned sensors have not been adapted toapplication in robot for joint torque detection. New slave arm
enabling to build in torque sensors is being developed. The 3Dmodel of anthropomorphic robot arm and shoulder withbuilt-in torque sensors is shown in Fig. 5.

DC motors
Harmonic drives withhigh reduction ratio

Optical torque sensors as
the output shafts ofharmonic drives
Fig. 5. 3D model of the new anthropomorphic robot arm.
The approach to designing a high-performance torquesensor for the anthropomorphic robot arm should follow theguidelines below.
1. Addition of the torque sensor to a robot joint should not
require redesign of the joint and should causes minimal
modification in kinematics and dynamics. A sensor with small
width and lightweight is desirable.
2. Noise created by current passing through the DC motorat each joint of the robot arm should not effect the sensing
element and use of electromagnetic sensors should be avoided
in this application.
3. The angle of twist of the movable part of the transducer
at the maximum expected external torque should enable
exploiting as wide a range of detector sensitivity as possible toachieve high signal-to-noise ratio.
4. Torsional stiffness of the sensor should notconsiderably reduce the natural frequency of the robot arm.
This introduces the trade-off of stiffness maximization while
maintaining high sensitivity.
5. The other difficulty in design of the torque sensor ishysteresis elimination. Most metals used as flexures have very

little hysteresis. Bolted, press fit and welded joints near the
flexure introduce hysteresis. Optimal design requires
realization of the mechanical structure from a single piece of
metal.
6. Influence from any of the nontorsional components ofload should be canceled to guarantee precise measurement of
torque T that is moment around Z-axis MZ in 6-axis sensors.
7. Behavior of the sensing element output and mechanicalstructure should be as close to linear as possible.
8. Simple to manufacture, low-cost, and robust.

designed to decrease the thickness of the transducer. The
layout of the structure having hub and three spokes (Y-shaped
structure) and adjustment mechanism of shield plate is shownin Fig. 8.
5

4

6
3

Y

RS

r

l

X

T

3.2. Development of New Torque Sensors
We decided to use ultra-small photointerrupters RPI-131
and RPI-121 as sensitive elements to measure the relative
motion of sensor components. The relationship between the
output signal and position of the shield plate for RPI-12116) isshown in Fig. 6. The linear section of the diagram
corresponding to 0.2 mm is used for detection of the relative
displacement of the object. The dimensions of thephotointerrupter (RPI-121 3.6 × 2.6 × 3.3 mm) and weight of
0.05 g enable realization of compact sensor design.

2

5

5
2

5
2

5
.
2

0
.
2

5
.
1

0
.
1

5
.
0

0
0

5
.
2

0
.
2

5
.
1

0
.
1

5
.
0

0
0

DISTANCE: d (mm)Fig. 6. Relative output vs. distance16).
Two elastic elements were realized to optimize the sensor
design: the in-line structure – when detector input and output
are displaced axially by thetorsion component and the “in3plane” one – when sensor
θ2
input and output are disposed2
in one plane and linked by
4
bending radial flexures. The
layout of the in-line structure
based on a spring with a5cross-shaped cross section isshown in Fig. 7. This spring1enables large deflections
without yielding. The detectorθ
T 1
consists of input part 1, output
3
part 2, fixed photointerrupters
Fig. 7. Construction of the 3, shield 4, and cross-shaped
optical torque sensor.
spring 5. The operating
principle is as follows: when torque T is applied to the input
shaft, the spring is deflected, rotating the shield 4. Shielddisplacement is detected by the degree of interruption of
infrared light falling on the phototransistor. The magnitude of
the photointerrupter output signal corresponds to applied
torque. The “in plane” arrangement of the load cell was

4tFig. 8. Layout of Y-shaped spring and position regulator.
The detector consists of inner part 1 connected by flexure
3 with outer part 2, fixed photointerrupter 5, slider with shieldplate 4, and screws 6. When torque is applied, radial flexures
are bent. The shield is adjusted by rotating oppositely locatedscrews 6. The pitch of screws enables smooth movement of theslider with the shield plate. The relationship between thesensed torque TS and the angle of twist θ is linear:
TS = kSθ = k S (θ1 − θ 2 ) ,

0
5

0
5

RELATIVE COLLECTOR CURRENT: Ic (%)

d

5
7

5
7
DISTANCE: d (mm)

0
0
1

0
0
1

RELATIVE COLLECTOR CURRENT: Ic (%)

5
2
1

5
2
1
d

1

(1)

where kS – torsional stiffness of flexure (Nm/rad).
Hub rigidity is increased by introducing additional evenly
distributed spokes17). The torsional stiffness of this sensor isderived from:⎛ 1 3r 3r 2 ⎞kS = 4 NEI ⎜ + 2 + 3 ⎟ ,
l ⎠
⎝l l

(2)

where N – number of spokes, l – the spoke length, E –modulus of elasticity, r – inner radius of the sensor6). The
moment of inertia of spoke cross section I is calculated as:I=bt 3 .
12(3)

Here b – beam width, t – beam thickness. The sensor was
designed to withstand torque of 0.8 Nm. The results ofanalysis using FEM show von Mises stress in MPa under atorque T of 0.8 Nm (Fig. 9a), tangential displacement in mm(Fig. 9b), von Mises stress under a bending moment MYZ of
0.8 Nm (Fig. 9c), and von Mises stress under an axial force FZof 10 N (Fig. 9d).

a)

c)

b)

d)
Fig. 9. Results of analysis using FEM.

Fig. 11. Test rig and calibration result.
The ring-shaped spring was designed to extend the
exploiting range of photodetector sensitivity while keeping
same strength and outer diameter. Components and assemblyof the developed optical torque sensor are shown in Fig. 12 (1– shield plate, 2 – photointerrupter RPI 131, 3 – ring-shaped
flexure). The flexible ring is connected to the inner and outerpart of the sensor though beams. Inner and outer beams are
displaced with an angle of 90° that enables large complianceof the ring-shaped flexure.

Y

The maximum von Mises stress under torque T of 0.8 Nm
equals σMaxVonMises = 14.57⋅107 N/m2 < σyield = 15.0⋅107 N/m2.
The angle of twist of 0.209° is calculated from the tangential
displacement. The ability to counteract bending moment isestimated by the coefficient:σ(4)
KTM = MaxVonMises (T ) .
σ MaxVonMises ( M YZ )Y-shaped spring coefficient KTM = 0.878. The same
approach to estimate the ability to counteract axial force FZ isapplied:σ(5)
KTF = MaxVonMises (T ) .
σ MaxVonMises ( FZ )After substitution of magnitudes, we calculate KTF = 11.44.
Our sensor was machined from one piece of brass using wire
electrical discharge machining (EDM) cutting to eliminate
hysteresis and guarantee high strength (Fig.10). In this sensor,
the ultra-small photointerrupter RPI-121 is used. The sensor isonly 6.5 mm thick.

2

1

X

T

3

Fig. 12. New topology and 3D model.
The results of analysis using FEM show von Mises stressin MPa under torque T of 0.8 Nm (Fig. 13a), tangential
displacement in mm (Fig. 13b), von Mises stress under
bending moment MYZ of 0.8 Nm (Fig. 13c), and von Mises
stress under axial force FZ of 10 N (Fig. 13d).

a)b)Fig. 10. Optical torque sensor with hub-spoke-shaped flexure.
In the test rig for calibrating the optical sensor (Fig.11),
force applied to the arm, secured by screws to the rotatableshaft, creates the loading torque. Calibration was realized byincrementing the angle of twist with small steps and measuring
the output signal from the photointerrupter.

c)d)Fig. 13. Result of analysis using FEM.

The maximum von Mises stress under torque T of 0.8 Nm
equals σMaxVonMises= 8.74⋅107 N/m2 < σyield = 8.96⋅107 N/m2.
Given structure provides the following coefficients KTM =0.217, KTF = 3.56 and angle of twist θ of 0.4°. Thus, thering-shaped structure enables magnifying the angle of twist
deteriorating degree of insensitivity to bending torque andaxial force. This structure was machined from one piece ofaluminium A5052. The components and assembly of the
optical torque sensor are shown in Fig. 14. The sensor is 10
mm thick. The displacement of the shield is measured byphotointerrupter RPI-131. The shortcomings of this design arecomplicated procedure of adjusting the position of the shieldrelatively photosensor and deficiency of the housing to preventfrom damage of the optical transducer.

Fig. 14. Optical torque sensor with ring-shaped flexure.

2

1

3
Y

X

Fig. 16. Semi-ring-shaped spring.
The results of analysis using FEM show von Mises stressin MPa under torque T of 0.8 Nm (Fig. 17a), tangential
displacement in mm (Fig. 17b), von Mises stress under
bending moment MYZ of 0.8 Nm (Fig. 17c), and von Mises
stress under axial force FZ of 10 N (Fig. 17d).

a)

b)

c)

d)

The setup in Fig. 11 was used to calibrate the sensor. The
relationship between angle of twist θ and the output voltage ofphotointerrupter is shown in Fig. 15.

Fig. 17. Results of analysis using FEM.
The maximum von Mises stress σMaxVonMises=14.94⋅107
N/m < σyield = 15.0⋅107 N/m2. The semicircular flexureprovides the following coefficients KTM = 0.082, KTF = 2.83
and angle of twist θ of 0.39°. This structure was machinedfrom one piece of brass C2801. Components and assembly ofthis optical torque sensor are shown in Fig. 18.
2

Fig. 15. Calibration result.
The sensor with a ring topology was modified. The layoutof the detector with semicircular flexure and 3D model are
given in Fig. 16 (1 – shield, 2 – photointerrupter RPI 131, 3 –semicircular flexure).

Fig. 18. Optical torque sensor with semi-ring-shaped flexure.
The sensor is 7.5 mm thick. Its drawback is highsensitivity to bending moment. The relationship between angle

of twist θ and the output voltage is shown in Fig. 19.

Fig. 19. Calibration result.
Technical specifications of optical torque sensors arelisted in Table 1.

large torsional stiffness diminishes photointerrupter resolution.
The semicircular spring has high sensitivity to bending
moment and axial force and small natural frequency. The
optimal solution is the ring-shaped flexure providing wide
torsional stiffness with high mechanical strength. The main
shortcoming of this topology is high sensitivity to bending
moment. Nevertheless, this obstacle is overcome throughrealization of a simple supported loading shaft of the robot
joint. In most loaded joints, e.g. shoulder, such material as
hardened stainless steel can be used for elastic elements tokeep sensor dimensions. Our optical sensors compared tostrain-gauge-based sensor ATI Mini 40 have small torsional
stiffness and low factor of safety. Nevertheless such
advantages as low cost, easy manufacture, and compactness
make them preferable for torque measurement in robot arm
joints. The linear transfer characteristic of the photointerrupter
simplifies calibration of the sensor.

4. Local Impedance Control

Table 1. Technical specifications
SensorSpring member
material
Photointerrupter
type
Load capacity,
Nm
Torsional
stiffness,
Nm/radNaturalfrequency, kHz
Factor of safety
Outer diameter,mm
Thickness, mm
Sensor mass, g

Hub-spoke
springRing-shaped
springSemicircularspringBrass C2801

Aluminium A5052

Brass C2801

RPI-121

RPI-131

RPI-121

0.8

0.8

0.8

219.8

115.86116.99

5.25

2.7

1.37

1.0

1.0

1.0

42

42

42

6.5
34.7

10.0
28.7

7.5
36.8

Table 2. Technical specifications of 6-axis force sensors
Sensor

ATI Mini 40
Y-shaped beam

Spring member
material

Hardened
stainless steel
Silicon strain
gauge

Sensing range
MZ, NmTorsional
stiffness Z-axis,
Nm/radNaturalfrequency, kHz
Accuracy, %Factor of safety
Outer diameter,mm
Thickness, mm
Sensor mass, g

FEXT
Jdi

The technical specifications of 6-axis force/torque sensors
with a similar sensing range of torque around Z-axis are listed
in Table 2 [11,18,19].

Sensing element

The objective of impedance control is to establish the
dynamic relationship between position error and force error ininteraction similar to Newton`s second low of motion. The
graphical presentation of local impedance control is given in
Fig. 20.

1.0

BL Autotec
Mini 2/10
Y-shaped beam

Minebea
OPFT-50N
Y-shaped beam

Stainless steel

Aluminium

Strain gauge

LEDPhotodetector

1.0

2.5

3.2
5.0

1.0
5.0

5.0
1.5

40

40

50

12.25
50

20
90

31.5
133

The spoke-hub topology enables a compact sensor. The

Jd(i+1)
τ EXT (i+1)

Ddi
Kd(i+1)
τEXTi

Kdi

Fig. 20. Concept of the local impedance control.
In joint space desired dynamics of robot joint i is:τ EXTi = J di ∆θi + Ddi ∆θi + K di ∆θ i ; ∆θ i = θ ci − θ di ,(6)

where τEXTi – torque applied to joint i caused by external force
FEXT, Jdi – desired inertia, Ddi – desired damping, Kdi – desired
stiffness, θci – output joint angle of the impedance model, θdi –desired joint angle. The state-space presentation of theequation of local impedance control is written:⎡ ∆θi ⎤ ⎡ 0⎢ ⎥=⎢⎣ vi ⎦ ⎣ − K d J d4300

Dd(i+1)⎤ ⎡θi ⎤ ⎡ 0 ⎤+τ (t ) , (7)− Dd J d ⎥⎦ ⎢⎣ vi ⎥⎦ ⎢⎣1 J d ⎥⎦ EXTi
1

where the state variable is defined as vi = ∆θi .
After integration of (7), the discrete time presentation of
the impedance equation is expressed as:⎡ ∆θ k +1 ⎤⎡ ∆θ k ⎤⎢ ∆θ ⎥ =Ad ⎢ ∆θ ⎥ + Bd TEXT ( k ) .
⎣ k +1 ⎦⎣ k⎦(8)where Ad and Bd – matrixes mapped by discretization, TEXT(k)– measured external torque. To verify the dynamic behavior of
the optical torque sensors, the local impedance control of links
of a simple SCARA manipulator was implemented (Fig.21,
torque sensors are marked by ovals). Speed reducers with gear
ratios of 2548 were selected to guarantee very low backdrivingof joints.

are placed coaxially with joint axes, they will be subjected togravitational force of neighboring links. This will also be
included in our future work.
References:
1)

2)
3)
4)

5)
6)

Fig. 21. SCARA type manipulator.

7)

The position-based local impedance control is shown in
Fig. 22 (KP and KD – proportional and derivative feedback
gains). The second-order low-pass filter was implemented toeliminate the noise component with a cutoff frequency of 80
Hz.

8)New optical torque sensors to replace thestrain-gage-based 6-axis force/torque sensor and realize virtual
backdrivability of joint transmissions have been developed.
These sensors are compact, lightweight, easy to manufacture,and have good linearity, enough resolution, andelectromagnetic noise immunity. Position-based local
impedance control of a SCARA manipulator has beensuccessfully implemented. Real-time computation of inverse
dynamics of the robot is not required that greatly decrease
computation time. The new anthropomorphic arm with ability
to build in developed torque sensors has been designed. New
research will realize of the local impedance control of eachjoint of the anthropomorphic robot arm which precise 3D
drawings using CAD is shown in Fig. 5. When torque sensors∆ θ k+1

Digital low-pass filter

θc

θd

12)
13)
14)
15)
16)
17)
18)

19)

A/D

Optical torquesensorAMP∆ θ k+1 ∆ θ k+1

θdTargettrajectory
generator

10)
11)

5. Conclusions

Impedance
trajectory
generator

9)

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θc

Kv

θd
θ

Kp

1
Ki KT

D/A

DriverθcsFig. 22. Block diagram of position based local impedance control system.

θ

Encoderim

Link