Transcript design and implementation of the system

Singularity Avoidance by Inputting Angular
Velocity to a Redundant Axis During
Cooperative Control of a Teleoperated DualArm Robot
Masanori Hayakawa, Keiko Hara, Daisuke Sato, Member, IEEE,
Atsushi Konno, Member, IEEE
and Masaru Uchiyama, Member, IEEE
Student ID ： M9920103
Student
： Kun-Hong Lee
Adviser
： Ming-Yuan Shieh
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Outline
ABSTRACT
 INTRODUCTION
 A TELEOPERATED DUAL-ARM SPACE
ROBOT
 SYSTEM DESIGN AND
IMPLEMENTATION OF THE SYSTEM
 EXPERIMENTAL RESULTS
 CONCLUSION
 REFERENCES

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ABSTRACT

This paper describes a procedure of avoiding singularity
for a redundantly-driven, dual-arm, master-slave robotic
system.

In cooperative operation, the procedure starts with a
periodic check if one of the dual arms is close to a
singular configuration by examining the manipulability of
the arm.

Experimental examples are provided to demonstrate
the proposed method.
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INTRODUCTION

In this research, the singularity avoidance support
system is developed on these backgrounds.

This system has the following features:

First of all, when a arm is close to singular configuration,
this system makes arm stop moving and control scheme
switches to redundancy control.

Secondly, this system shows operator the possible arm
configuration during singularity avoidance in advance.
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INTRODUCTION

And the operator can select the arm configuration from
them. Then, by inputing angular velocity to a redundant
axis, new configuration is allowed, while preservin
desired internal forces.

Finally, this system makes arms move toward the
selected arm configuration.

In this paper, the concept of the singularity avoidance
support system is to develop a supporting function for
human to manipulate robot easily.
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A TELEOPERATED DUAL-ARM
SPACE ROBOT SYSTEM
Fig. 1. Overview of the experimental teleoperation system.
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A TELEOPERATED DUAL-ARM
SPACE ROBOT SYSTEM

A concept of teleoperated dual-arm space robot system
is shown in Fig. 1. This system is divided into a slave
system and a master system.

In order to study a time delay problem between a space
robot and a teleoperation system on the earth, the
dual-arm space robot system can incorporate any length
of time delay between the master and slave systems.

A model based teleoperation is introduced to avoid
instability caused by the time delay.
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A TELEOPERATED DUAL-ARM
SPACE ROBOT SYSTEM

The model based teleoperation system involves a virtual
environment of the dual-arm robot in the computer of
the master system.

The operator watches virtual environment displayed on
monitor and controls the slave arms by using the
master arms.
Fig. 2. Overview of the virtual environment
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A TELEOPERATED DUAL-ARM
SPACE ROBOT SYSTEM

The slave system consists of two slave arms, 6-axis force
sensors, and a computer to control the slave arms.

The PA10 manipulators manufactured by Mitsubishi
Heavy Industries, Ltd are used as the slave arms.

As the PA10 has 7-DOF, it is possible to avoid the
singular configuration by using redundancy without
moving end-effector.

Two force sensors are attached on the wrist of each
slave arm.
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A TELEOPERATED DUAL-ARM
SPACE ROBOT SYSTEM

The joints of PA10 are called, respectively, from the root
of arm, S1, S2, S3, E1, E2, W1, W2 and shown in Fig. 3.
Fig. 3. Name of joints.
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A TELEOPERATED DUAL-ARM
SPACE ROBOT SYSTEM
A.Cooperative Control of the Dual-Arm Robot

As mentioned above, a model based teleoperation is
introduced to overcome the time delay problem.

The motion command generated by operating the
master arm is sent to both arms in virtual environment
(virtual arms) and arms in slave system (slave arms).

Fig. 4 shows the coordinate systems when the slave
arms grasp an object.
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CONTROL SCHEME
A. Cooperative Control of the Dual-Arm Robot

As mentioned above, a model based teleoperation is
introduced to overcome the time delay problem.

The motion command generated by operating the
master arm is sent to both arms in virtual environment
(virtual arms) and arms in slave system (slave arms).

Fig. 4 shows the coordinate systems when the slave
arms grasp an object.
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CONTROL SCHEME
Fig. 4. Coordinates of the system in capturing the object.
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CONTROL SCHEME

As shown in Fig. 4, the right and left virtual arm, slave
arm, and master arm are named Vir Arm 1,Vir Arm 2,
Arm 1, Arm 2, and Master Arm 1, Master Arm 2
respectively.

Where Σ0 is the base coordinate system of the slave
system, Σa is the coordinate system of holding object. Σh1
, Σh2 are the coordinate systems of end-effector of Arm
1, Arm 2. Σm1 , Σm2 are coordinate systems of Master
Arm 1 and 2, respectively.
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CONTROL SCHEME

In this control scheme, the motion of the holding object
is controlled by operating the Master Arm 2.

Conversion from the cooperative mode to the
redundancy control mode is carried out by using the
jog-dial attached on the master arm. Detail of it is
explained later.

For internal force and relative position controls, the
desired force and position vector are decided previously.
Switching betweeninternal force and relative position
controls is done by GUI.
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CONTROL SCHEME


B. Redundancy Control in the Cooperative DualArm Robot
θr, 7×1 joint angular velocity vector in null-space of J, is
given by (1) when Jacobian matrix of a 7-DOF
redundant manipulator is expressed as J,
ξ is a 7 × 1 arbitrary vector. The way to calculate ξ is
shown in (2), and V (θ) is manipulability measure, shown
as (3).
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CONTROL SCHEME

Then scalar value k is derived as follows. Since ˙θr is in
the null space of J, ˙θr can not affect on the end-effector
velocity ˙p, i.e. J˙θr = 0. Therefore ˙θr given by (1) is
utilized to avoid singularity. The joint angular velocity
command is given as follows.
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CONTROL SCHEME
(a) S1 and S3 rotate
about the same axis,
and S1 is at 0 or 180
(◦). Moreover S3 is at
90 (◦) rotation from S1.
(b) E2 and W2 rotate
about the same axis,
and W2 is at 0 or 180 (◦).
Moreover E2 is at 90 (◦)
rotation from W2.
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CONTROL SCHEME
(c) S3 and E2 rotate
about the same axis.
(d) S1 and S3 rotate
about the same axis,
and E2 and W2
rotate about the
same axis.
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CONTROL SCHEME
(e) S1, S3 and W2
rotate about the same
axis.
(f) S3, E2 and W2
rotate about the
same axis.
Fig. 5. Singular configuration of PA10.
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CONTROL SCHEME

In this control scheme, the motion of the holding object
is controlled by operating the Master Arm 2.

Conversion from the cooperative mode to the
redundancy control mode is carried out by using the
jog-dial attached on the master arm. Detail of it is
explained later.

For internal force and relative position controls, the
desired force and position vector are decided previously.
Switching betweeninternal force and relative position
controls is done by GUI.
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EXPERIMENT
A. An Experimental Methodology
 In this experiment, while slave arms are holding object
using internal force control, redundancy control is
carried out by inputing joint angular velocity from
master arm to redundant axis of slave arm.

By commanding plus and minus angular velocity to Arm
1 and Arm 2, redundancy control is executed.
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EXPERIMENT

In this experiment, desired internal force is 50.0 N in
the direction of xa with respect to Σa , and desired
internal forces and moments for other directions are 0
N and 0 Nm respectively. Holding object is
590×20×200 mm rectangular solid styrene foam.

Both side of styrene foam are gripper points and
covered with acrylic plate, size of 2×200×200 mm. As a
result the gross weigh of holding object is 1.23 kg. As
gripper points are covered with acrylic plate, grip force
is not absorbed so much.
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EXPERIMENT
B. Results of Experiment
 This interval (i) is indicated in Fig. 9 and Fig. 10. Fig. 8
shows that master arm commands plus and minus
angular velocity to S3 axis of of Arms 1 and 2.
Fig. 8. S3 angular velocity commanded
from the master arm.
Fig. 9. Internal force in the
direction of xa.
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EXPERIMENT
B. Results of Experiment
 Fig. 9 shows that the desired and current internal force
in the direction of xa keep around 50 N during the
interval (i). As shown in Fig. 10, indicate position and
orientation of the end-effector of Arms 1 and 2, They
are nearly stationary during the interval (i).

This experiment proves that redundancy control, by
using proposed control scheme, is carried out with
stabilizing internal force. It means that by commanding
angular velocity to redundant axis, the operator can
change the arm configuration without interfering
cooperative control of dual-arm.
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EXPERIMENT
A.
An Experimental Methodolo
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SYSTEM HARDWARE
C. BOSU Balance Training Platform
Fig. 2. (a)–(d) Technical drawing of the BOSU balance trainer [16]. (e) FSP mounted
on the balance trainer for acquisition of readings in perturbed conditions. (f) Subject
mounted on the BOSU balance trainer that has been fitted with the FSP and use of
hand rails for additional safety support in dynamic condition.
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DESIGN AND IMPLEMENTATION
OF THE SYSTEM
Fig. 3. Flow chart describing the force-sensing system’s functionality.
Analog signals are acquired by the FSRs on the FSP and digitized
before making the data available for real-time/ postacquisition analysis.
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DESIGN AND IMPLEMENTATION
OF THE SYSTEM
A. Real-Time Visual Representation of Pressure
Profile

The designed system presented visual feedback to end
users in real time.

Real-time visual data representation was useful in
providing qualitative assessment of subjects’ postural
control and pressure points.
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DESIGN AND IMPLEMENTATION
OF THE SYSTEM
A. Real-Time Visual Representation of Pressure
Profile

A rainbow color scale was used to represent low force
intensities with colors close to black (cold colors) and
high force intensities with colors close to white (hot
colors).

This form of real-time feedback to end-users [see Fig.
4(a)] eases the process of identifying regions with high
force concentrations at the foot.
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DESIGN AND IMPLEMENTATION
OF THE SYSTEM
A. Real-Time Visual Representation of Pressure
Profile
Fig. 4. (a) Snapshot of the IGUI feedback displaying real-time captured foot patterns
with varying color intensities to represent regions of high force concentrations. (b)
Reproduced foot boundary from reduced data set; migration of weighted center of the
applied pressure over time was superimposed on the traced foot boundaries.
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DESIGN AND IMPLEMENTATION
OF THE SYSTEM
B. Off-Line Representation of Pressure
Concentration Sites

Stored signals were retrieved for analysis using MATLAB
R2009b and checked for redundancy.

Redundancy in the data sets referred to regions of the
FSP that did not come in contact with the subjects’ foot.
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DESIGN AND IMPLEMENTATION
OF THE SYSTEM
B. Off-Line Representation of Pressure
Concentration Sites
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DESIGN AND IMPLEMENTATION
OF THE SYSTEM
B. Off-Line Representation of Pressure
Concentration Sites
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DESIGN AND IMPLEMENTATION
OF THE SYSTEM
B. Off-Line Representation of Pressure
Concentration Sites

The X plane on the platform corresponds to the ML
anatomical plane, while the Z plane refers to the AP
anatomical plane.
Fig. 5. Sectioned view of the FSP, depicting the arrangement of four
FSRs, and the magnitude and location of the resultant force Fy , when
FSRs are pressed.
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DESIGN AND IMPLEMENTATION
OF THE SYSTEM
C. Fuzzy Clustering

The FCM algorithm was used in this paper to identify 2D regions with repeating locations of data
concentration (pressure concentration) along the ML
and AP planes.

The objective function used was the distance from any
given data point to a cluster center, weighted by that
data point’s membership grade.
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EXPERIMENTAL RESULTS
A. Real-Time Qualitative Assessment
Fig. 6. Real-time view of the IGUI provided to the end-user. The IGUI allows
for the rainbow color scale graph to be rotated, and viewed as a 3-D graph for
ease of visualization (a) Default acquisition view: EO. (b) Default acquisition
view: EC. (c) Rotated acquisition view: EO. (d) Rotated acquisition view: EC.
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EXPERIMENTAL RESULTS
B. Pressure Concentration Sites
Fig. 7. Single representative subject’s zoomed-in view on the distribution
of COP plotted on a coordinate scale in units (1 unit = 40 mm). (a) Left
foot. (b) Right foot.
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EXPERIMENTAL RESULTS
C. Clustering Distribution Sites
Fig. 8. Fuzzy clustering applied to the calculated pressure distribution
coordinates to identify occurrences of clusters within data set in EO
state while subject is on static surface. (a) Left foot (b). Right foot.
Identified clusters are marked as black dots on the graph.
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EXPERIMENTAL RESULTS
D. Lifestyle and Postural Control
Fig. 9. Average distribution area of COP of all subjects sorted from “active”
to “inactive” lifestyle along the x-axis. (a) Static condition, EO. (b) Static
condition, EC. (c) Dynamic condition, EO. (d) Dynamic condition, EC.
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CONCLUSION

The results obtained demonstrated the sensitivity of the
developed system toward changes made in the postural
control system.

Individual with or without balance disorder could
benefit by relying on the measurements of the system
to identify, correct, monitor, and suggest improvements
for problems with the proprioception response of the
feet, which influences the postural control and
occurrences of foot related injuries.
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Tthank you
for your attention
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