A collaborative-shared control system with safe obstacle ... - IEEE Xplore

Proceedings of the 2004 IEEE Conference on Robotics, Automation and Mechatronics Singapore, 1-3 December, 2004

A Collaborative-Shared Control System With Safe Obstacle Avoidance Capability Jian Shen, Javier Ibanez-Guzman, Teck Chew Ng

Boon Seng Chew

Mechatronics Group

School of Electrical and Electronic Engineering

Singapore Institute of Manufacturing Technology

Nanyang Technological University

Singapore

Singapore

Abstract-Tele-operated

systems

allow humans

to extend

their physical capa bi iities and enable them to intervene in hazardous operations or where their presence is not possible. However, the operation of such systems over long periods has proved to be difficult and stressful.

Consequently, means to

subj ect

time when facing problems during the opera ti on Both the robot and the human operator are treated as one unit in order to achieve an assign ed task. With shared control, an .

intennediate level of autonomy to the direct and supervision control strategies is provided. Under the shared control

robust. [n our method, the Collaborative Control component is

sch eme a human operator shares the control of the system with the robot by using Haptic display and sensor feedback. With sensor feedback and haptic display, a human operator will be virtual presence in handling the system. In addition, the shared control scheme generates an automatic control

responsible for allowing operator intervention when the robot is

mechanism to secure the robot in an expected manner. For this

facing complex situations, whilst the Shared Control component

purpose, we developed a hybrid obstacle avoidance algorithm to improve the system's reliability and efficiency.

facilitate

their

use

experimental work.

are

the

of

much

In this paper, we propose

a

study

and

collaborative­

shared control strategy that combines the operator abilities with robotic-based tasks to render these systems more flexible and

provides an automatic control mechanism

to

assist and

to

monitor-correct irrational operator actions. The paper will demonstrate how collaborative and shared control strategies work together to facilitate the telcoperated control of a mobile platform in a cluttered environment.

The

experimental results include applications to surveillance and to

,

This paper presents a method that combines the shared control with collaborative control scheme. As deriving advantages from the respective control scheme, the method makes the system flexible, reliable and efficient in the man­ machine interaction op erations .

-II.

search & rescue operations. In addition, a key component in the

form

of a hybrid obstacle avoidance module is introduced that

METHOD

allows the robot to be guided on a task basis by the operator at a

A.

distance.

The system consists of two parts: control console and ATRV robot (see Fig. I). We installed analog transmitters for

Keywords-shared control; collaborative control; obstacle

Tete-Robotic System Setup

avoidance; teieoperation; autonomous; mobile robot

1.

INTRODUCTION

Tele-robotics has been widely implemented in many applications. It involves a human operator controlling a robot remotely through joysticks or alternative devices such as mouse and microphone. Supervisory control, as introduced by Sherdan in 1992, was a popular method in the tele-robotic application. With this method, human control and mechanized control are combined to achieve a goal. A human as a supervisor, makes changes to the state of the controller through a man-machine interface and monitors the status of ,

the co n trolled system for unexpected behaviors. Recently, shared control [1-4] and. collaborative control [5-9] for tele robotic applications generated much interest and were widely studied and implemented. With collaborative control, human responses are treated as a resource for the robot. Being a resource to the robot, the main task of a human operator is to make decisions and to provide solutions to robot's queries. The robot will trigger the human operator for assistance at any ­

0-7803-8645-0/041$20.00 © 2004

IEEE

Figure I. System setup video communication, and wireless LAN for data conununication. In the control console, varieties of input

119

hardware such as mouse, joystick, microphone and touch screen was used to control the robot. Accordingly, we added SICK laser and DIGICLOPS on the robot for perception, electrical compass and optical gyro for pose estimation as well as a camera for visual assistance when manually driving or monitoring. B.

operation system. The main objective of this mechanism is to achieve flexible and reliable control of the mobile robot. With the collaborative control, an operator commands the robot to Statlls Constraint query

Sensor data display Action query

System Architecture

We adopt clientJserver architecture for the system (Fig. 2).

A server process runs on the robot's onboa rd computer and provides basic services including motion control, localization, sensor management and status. In order to get rid of the influence of wireless communication delay, the obstacle avoidance algorithm is embedded to the server process. A client process runs on the console computer and controls

control,

"high-level" operations including task-level 10caVglobai mapping and decision-making.

Operator

ROBOT

Figure 3. Contwl and infonnation flow

carry out a specific task such as path following, vehicle following or way point navigation. etc. The operator also monitors the status of the mobile robot. Whilccarrying out the commanded task, the mobile robot may encounter some difficult situation, such as low battery level; a series of decision-making questions will be prompted, as shown in Fig. 4, for the operator. At this point, the operator integrates

Figure 2. System architecture

himself into the control loop by making

C.

the appropriate

Collaborative-Shared Control

Traditionally, the robot was always treated as a tool or slave to the human operator under supervisory control scheme. The robot was commanded to perfonn any tasks by the operator without considering the capability limitation of the robot. To have an effective working relationship between the operator and the robot, the collaborative control concept was

introduced [5-9]. The robot was considered as a working partner" rather than a tool in this scheme, There was communication flow between operator and robot. Both operator and robot collaborated with each other in solving problems and achieving common goals, However, unlike "

robot, an operator would get tired eventually during the operation. To solve this problcm, shared control scheme was introduced into the system, The robot was given some degree of autonomy in making decisions to solve some trivial

Figure 4. Examples of questions

problems rather than having the operator give instructions.

Having studied the advantages of the combination of the above two control schemes, we designed and implemented a collaborative-shared control mechanism (Fig. 3) to the tele-

decision.

Hence,

the

from the

robot

collaborative' control

mechanism

integrates the operator capability to compensate some of the inabilities of the robot. However, the efficiency of the overall

120

operation will be degraded, as too much operator assistance is needed. The introduction of the shared controller scheme can

Start

overcome this shortcoming by transferring more autonomy to the robot itself. For this purpose, we develop a hybrid obstacle

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avoidance algorithm that can deal with complex situations to ensure the robot moving safely whenever in manually or autonomously driving. Hence, the robot will only need a little assistance from the operator. The algorithm details will be

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introduced in the following section. D.

Obstacle Avoidance Algorithm in Shared Control

We analyzed the Vector Field Histogram (VFH) algorithm and the Modified Distance Transfonn (MDT) algorithm. Experiments showed that the VFH faced threshold tuning difficulties whcn at T-shaped junctions while the MDT made

FIFOstaek

the robot move too close to the obstacles. Our approach is to hybridize the VFH with MDT. Before presenting how two algorithms are combined, we introduce the two algorithms

End

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Figure 5. MDT processing procedure 1-3

first. •

Modified Distance Transform algorithm [10-11]

The algorithm begins with an initialization of a 2D mxn

grid map into cells CLij [where (i, j) is found on the coordinate (m, n)] with a cell traversal cost of Cij and a cell target value TVij initialized to a very large number k. represents the minimum total traversal cost from the cell

TVij

CLij

to the end point cell. C-space is the area expanded from

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