gravity compensation and compliance based force control for auxiliarily easiness in manipulating...

Gravity Compensation and Compliance Based Force Control forAuxiliarily Easiness in Manipulating Robot Arm

Student ID MA020213

Student 莊沛語Teacher 謝銘原

OutlineOutline

Abstract Introduction GRAVITY COMPENSATOR A System structure B Denavit - hartenbergrsquo form D Auxiliary torque compensator

IMPEDANCE CONTROL FORCE COUNTERBALANCE CONTROL CONCLUSIONS REFERENCES

AbstractAbstract

The objective of this paper is to present the gravity compensation and compliance based force control for auxiliarily easiness in manipulating robot arm

Haptical application of the safety-priority robot arm technique which interacts with people must reduce the ear ratio and design necessary algorithm which can provide auxiliarily easiness in moving the robot arm especially during the teach and learning mode

In this study discuss the effects of two aspects and propose a control algorithm to improve efficiency of carrying heavy item Firstly the gear ratio of motor is bounded so that robot can be more flexibly compliant while user take grip on it

To solve this problem of gravity compensation we propose a method that based on the concept of vector projection to calculate a general solution which can construct a gravity model of multi-DOF robot arm

Furthermore we define a virtual mode that is proposed to compensate the deficiency of inertiarsquos physical phenomenon

Secondly propose an approach which call it force counterbalance control (FCC) that not only balances external load variation in addition to robot weight itself but also keeps the property of dexterous easiness in manipulating the multi DOF robot arm

The FCC algorithm can be applied on several applications such as carrying heavy item or being auxiliarily easinese in manipulating robot arm

IntroductionIntroduction

Robot arm is widely used in different fields of application from industrial automation to domestic service In past time traditional robot arm have been focused on stiff transmission rapid movement and high accuracy Recently researchers begin to put more emphasis on the robot armrsquos safety and reliability

The actuators are often used to drive the hardware of the robots actuator control is one of the most important issues and actuators are always used by motor hydraulic Pneumatic and so on

In the part of control a lot of control methods are proposed by robotics researchers like Impedance Control Admittance Control (position based control) Force Control Stiffness Control forceposition Control and even Hybrid control

The control algorithms that are mentioned above always suffer in some physical disturbance such as gravity Coriolis force and friction force

The gravity compensator is an indispensable issue some researchers use special control algorithm that takes into account the maximum admissible payload to reduce the disturbance of gravity or use the concept of energy or use Lyapunov control theorem to compensate

The gravity compensator is based on dynamics Vector projection is fully utilized to accurately compute the torque value that each joint have to be compensated Thus the gravity compensator can be real time compensated in any position If the gravity compensator is correct the robot manipulator can stop in any position after it is moved to any position

Beside of adding gravity compensator we also add a new method auxiliary torque compensation to compensate the deficiency that is caused by gear ratio Contributed by the compensation the robot manipulator can be moved freely and lightly

GRAVITY COMPENSATOR

A System structure In structure of the control

system which is based on 6- DOF arm use PCI base motion control card that provide the powerful real time calculating capability to program the self design control algorithm

Fig 1 Control Structure

The motion control card provides 1ms servo interrupt time for the routine of the control and sends out the control command to the servo driver through the DA converter The servo driver is configured to the mode which receives the torque command The test platform of arm is actuated by servo motor with 50 ratio harmonic drives which is in between the arm and servo motor So use torque mode to drive motor and gave robot manipulator some force compensator

TABLE I

All of the physical model parameters of the system show in the Table and the Fig show the each link and each axis of robot manipulator such as Link1 link2 kink3 axis1 axis2 axis3 axis4 axis5 axis6

Fig 2 6 DOF Robot arm model TABLE II

B Denavit- hartenbergrsquo form

The robot arm is designed with 6-DOF to reach attempted point in 3D space In order to understand the dynamic state of the robot every joint space relationship must be established from base to end effector

Fig 3 (a) 6 DOF Robot arm model

Relationship between every link coordinate systems of the 6- DOF arm using the Denavit - Hartenberg convention The values of the kinematic parameters are listed in Table where d1 d3 and d5 are the link lengths of base to shoulder shoulder to elbow and elbow to wrist respectively

TABLE III

And then they correspond to the position in the link coordinate diagram of The D-H convention allows the construction of the forward kinematics function by composing the coordinate transformations into one homogeneous transformation matrix

(b) 4 axis Coordinate systems of the robot

(1)

(2)

C Gravity compensator

The general control block diagram is All of robot manipulator controls always suffer in external disturbance such as gravityG(q) damping and even CoriolisforceC(q q1048581) that are caused by angular velocity and linear velocity the damping can be reduced by low gear ratio and the Coriolis force is too small to be eliminated in this system

Fig 4 Control block diagram

Because the gripper is too light to ignore just consider axis1 to axis 4 The coordinate transformation shows in Fig Then the dynamics is used to compute the compensator of gravity

Gravity has relationship with each joint so we base on the concept of following with Fig

1 Base coordinate bases on X0 Y0 and Z0

2 Gravity always points to X0 of base coordinate

3 The torque that one joint sustains is the moment projection that relatives this joint

In Fig 6 F means a force vector in 3D space r means nearest distance vector of 3D space and e means the unit projection vector so the equation of the moment in 3D space is got form Fig1048581

bull The moment size that projects along unit vector can be computed with and 1048581 by inner product in (4)

(3)

(4)

(5)

Where means projection vector of torque Base on the concept of (4) and (5) expand the single axis to multi-DOF axes and compute the torque of each axis that gravity causes

F is equivalent to each link weighting R is equivalent to the center of each link and e is equivalent to the unit vector of motor of each joint F r and e of every joint can be computed form Fig5 (b) and (6) (7)

(6)

(7)

By (8) (9) (10) each joint torque that have to be compensated by motor can be obtained with Fig7

(8)

(9)

(10)

Fig 7 The physical features of every axis

D Auxiliary torque compensator In the condition of senseless the gear ratio make the robot manipulator

is manipulated difficultly on haptical control Therefore the methods that are angular momentum and angular impulse principle and parabolic curve are proposed to deal with this damper question

Therefore bring up a method of parabolic curve to solve above problem and the parabolic curve is shown in Fig8

Fig 8 The parabolic curve that be looked on as auxiliary force

In a word the dexterous gravity compensator is obtained by gravity compensator parabola function and angular momentum and angular impulse principle shown in Fig9


IMPEDANCE CONTROL

In order to measure the torque that is caused by external weight we use the closed loop system of impedance control The definition of impedance control is the relationship between position and torque and the concept of impedance control is introduced by Hogan and is considered as a classical control in robotics The closed loop of impedance control is shown in Fig10

Fig 10 Impedance control

FORCE COUNTERBALANCE CONTROL A lot of workmen always have to carry heavy object it may cause

movement injury mindlessly because they have to make a power to move heavy item Therefore the method that combines the gravity compensator auxiliary torque compensator and impedance control is proposed to solve this question The force counterbalance control algorithm can increase force to arise heavy item and user can also freely move the manipulator that loads heavy item to some place where user wants The general block diagram of force counterbalance control is shown in Fig11

Fig 11 Force balance control

First impedance control is utilized to construct spring model we take the axis torques that above we can feel the movement of the robot manipulator that holds the heavy object is light and handy The flow diagram is shown in Fig12

Fig 12 Weight estimate algorithm

EXPERIMENT RESULT

(a) (b)

(c) (d)

(a) Moving robot manipulator freely and lightly by Auxiliary torque compensator

(b) Halting robot manipulator by gravity compensator (c) Adding a 25Kgw heavy object (d) Computing the weight of object and robot self by FCC (e) Moving the robot and object freely and lightly after adding FCC (f) Halting the robot and

Fig 13 Force counterbalance control experiment

(A)

(e) (f)

CONCLUSIONS

In this paper dexterous gravity compensator and FCC are proposed Many advantages of the algorithm are listed as follows

1 Because of the dexterous gravity compensator robot arm has good performance in compliance

2 The force counterbalance control (FCC) is helpful for arm to load weight payload and help people to move objects

REFERENCES [1] Physical Human ndashRobot Interaction Dependability and Safety httpwwwphriendseu [2] A Albu-Schaffer C Ott U Frese and G Hirzinger ldquoCartesian

Impedance Control of Redundant Robots Recent Results with the DLRLight- Weight-Armsrdquo IEEE International Conference of Robotics and Automation 2003

[3] B Heinrichs N Sepehri and AB Thornton-Trump ldquoPosition-Based Impedance Control of an Industrial Hydraulic Manipulatorrdquo IEEE nternational Conference on Robotics and Automation Minneapolis Minnesota April 1996

[4] A Kugi C Ott A Albu-Schaffer and G Hirzinger ldquoOn the Passivity- Based Impedance Control of Flexible Joint Robotsrdquo IEEE Transactions on Robotics April 2008 Volume 24 Issue 2 pp 416 ndash 429

[5] A De Luca S Panzieri ldquoA simple iterative scheme for learning gravity compensation in robot armsrdquo Proc of the 36th ANIPLA Annual Conf (Automation 1992) Genova I (1992) pp 459ndash471

[6] A De Luca S Panzieri ldquoAn asymptotically stable joint PD controller for robot arms with flexible links under gravityrdquo Proc of the 31st IEEE Conf on Decision and Control Tucson AZ (1992) pp 325ndash326

[7] Kelly R (1997) ldquoPD control with desired gravity compensation of robotic manipulatorsA reviewrdquo International Journal of Robotics Research 16(5) 660ndash672

[8] C Ott CAlbu-Schaffer A Kugit S Stramigiolit and GHirzinger (2004) ldquoA passivity based cartesian impedance controller for exible joint robotsmdashPart ITorque feedback and gravity compensationrdquo IEEE International Conference on Robotics and Automation pp 2659ndash2665

[9] L Zollo B Siciliano A D Luca E Guglielmelli and P Dario ldquoCompliance control for an anthropomorphic robot with elastic jointsTheory and experimentsrdquo ASME Journal of Dynamic Systems Measurements and Control 127(3) 321ndash328 2005

[10] N Hogan Impedance Control An Approach to Manipulation Part I-- Thoery Journal of Llynamic Systems Measurement and Control Yo1 IO pp 1-7 Mar 1985

Thanks for your patienceThanks for your patience

OutlineOutline

Abstract Introduction GRAVITY COMPENSATOR A System structure B Denavit - hartenbergrsquo form D Auxiliary torque compensator

IMPEDANCE CONTROL FORCE COUNTERBALANCE CONTROL CONCLUSIONS REFERENCES

AbstractAbstract
















GRAVITY COMPENSATOR





TABLE I







TABLE III



(1)

(2)











(3)

(4)

(5)



(6)

(7)


(8)

(9)

(10)








IMPEDANCE CONTROL








EXPERIMENT RESULT

(a) (b)

(c) (d)




(A)

(e) (f)

CONCLUSIONS















AbstractAbstract
















GRAVITY COMPENSATOR





TABLE I







TABLE III



(1)

(2)











(3)

(4)

(5)



(6)

(7)


(8)

(9)

(10)








IMPEDANCE CONTROL








EXPERIMENT RESULT

(a) (b)

(c) (d)




(A)

(e) (f)

CONCLUSIONS



























GRAVITY COMPENSATOR





TABLE I







TABLE III



(1)

(2)











(3)

(4)

(5)



(6)

(7)


(8)

(9)

(10)








IMPEDANCE CONTROL








EXPERIMENT RESULT

(a) (b)

(c) (d)




(A)

(e) (f)

CONCLUSIONS
















TABLE I







TABLE III



(1)

(2)











(3)

(4)

(5)



(6)

(7)


(8)

(9)

(10)








IMPEDANCE CONTROL








EXPERIMENT RESULT

(a) (b)

(c) (d)




(A)

(e) (f)

CONCLUSIONS





















TABLE III



(1)

(2)











(3)

(4)

(5)



(6)

(7)


(8)

(9)

(10)








IMPEDANCE CONTROL








EXPERIMENT RESULT

(a) (b)

(c) (d)




(A)

(e) (f)

CONCLUSIONS

















(1)

(2)











(3)

(4)

(5)



(6)

(7)


(8)

(9)

(10)








IMPEDANCE CONTROL








EXPERIMENT RESULT

(a) (b)

(c) (d)




(A)

(e) (f)

CONCLUSIONS

























(3)

(4)

(5)



(6)

(7)


(8)

(9)

(10)








IMPEDANCE CONTROL








EXPERIMENT RESULT

(a) (b)

(c) (d)




(A)

(e) (f)

CONCLUSIONS
















(6)

(7)


(8)

(9)

(10)








IMPEDANCE CONTROL








EXPERIMENT RESULT

(a) (b)

(c) (d)




(A)

(e) (f)

CONCLUSIONS
















(8)

(9)

(10)








IMPEDANCE CONTROL








EXPERIMENT RESULT

(a) (b)

(c) (d)




(A)

(e) (f)

CONCLUSIONS






















IMPEDANCE CONTROL








EXPERIMENT RESULT

(a) (b)

(c) (d)




(A)

(e) (f)

CONCLUSIONS




















EXPERIMENT RESULT

(a) (b)

(c) (d)




(A)

(e) (f)

CONCLUSIONS


















(A)

(e) (f)

CONCLUSIONS















CONCLUSIONS















gravity compensation and compliance based force control for auxiliarily easiness in manipulating...

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