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Research article
A hybrid pole climbing and manipulating robot with minimum DOFs for construction and service applications
M. Tavakoli, M.R. Zakerzadeh, G.R. Vossoughi and S. Bagheri
Sharif University of Technology, Tehran, Iran
Abstract
Purpose – Aims to describe design, prototyping and characteristics of a pole climbing/manipulating robot with ability of passing bends and branches of the pole.
Design/methodology/approach – Introducing a hybrid (parallel/serial) four degree of freedom (DOF) mechanism as the main part of the robot and also introduces a unique gripper design for pole climbing robots.
Findings – Finds that a robot, with the ability of climbing and manipulating on poles with bends and branches, needs at least 4 DOFs. Also an electrical cylinder is a good option for climbing robots and has some advantages over pneumatic or hydraulic cylinders.
Research limitations/implications – The robot is semi-industrial size. Design and manufacturing of an industrial size robot are a good suggestion for future works.
Practical implications – With some changes on the gripper module and the last tool module, the robot is able to do some service works like pipe testing, pipe/pole cleaning, light bulb changing in highways etc.
Originality/value – Design and manufacturing of a pole-climbing and manipulating robot with minimum DOFs for construction and service works.
Keywords Design, Parallel programming, Kinematics, Poles, Robotics
Paper type Research paper
178
Introduction
Climbing robots have received much attention in recent years due to their potential applications in construction and tall building maintenance, agricultural harvesting, highways and bridge maintenance, shipyard production facilities, etc.
Use of serial multi-legged robots for climbing purposes requires greater degrees of freedom (DOFs), without necessarily improving the ability of robots to progress in a complex workspace. It is also well known that serial configurations demand a greater amount of torque at the joints, thus calling for larger and heavier actuators and resulting in smaller payload to weight ratio, which is critical in climbing robots. In contrast using parallel platforms can result in the decrease of the weight/power ratio, thus allowing for larger payloads.
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Earlier research in this area has focused on six-DOF universal prismatic spherical (UPS) mechanisms (Merlet, 2000; To¨ nshoff, 1998).
Saltare′n et al. has modeled and simulated a parallel six- DOF parallel robot with pneumatic actuators. The modeled robot has a large payload capacity which is an important issue for industrial pole climbing robots (Salataren et al., 1999).
Later Aracil et al. fabricated a parallel robot for autonomous climbing along tubular structures. This robot uses the Gough- Stewart platform as a climbing robot. The platform actuators are six pneumatic cylinders with servo control. Their mechanism also used six cylinders as the grippers (three cylinders for each gripper) using a total of 12 actuators not counting the actuators needed for the manipulator arm (Aracil et al., 2003). The mechanism is rather complicated and has the ability of passing bends in any direction, making it suitable for traveling along trees and complex structures. So there is a need for a less complicated robot, which has the ability of traveling along human made and less complicated structures with minimum DOFs and minimum number of
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Industrial Robot: An International Journal 32/2 (2005) 171– 178
q Emerald Group Publishing Limited [ISSN 0143-991X] [DOI 10.1108/01439910510582309]
This paper was first published at CLAWAR 2004, 7th International Conference on Climbing and Walking Robots and the Support Technologies for Mobile Machines, 22-24 September 2004, Madrid, Spain.
This work has been made possible by a grant from the Tavanir Electric research Center. The authors would like to thank Tavanir for supporting this research.
A hybrid pole climbing and manipulating robot
M. Tavakoli, M.R. Zakerzadeh, G.R. Vossoughi and S. Bagheri
Industrial Robot: An International Journal
Volume 32 · Number 2 · 2005 · 171– 178
actuators. Furthermore, using pneumatic cylinders in the mechanism has the problem of transferring compressed air from the compressor to the cylinders.
But in recent years some industrial applications such as machine tools have resulted in more attention to parallel mechanisms with less than six DOFs. Most of the research in recent years have focused on three-DOF mechanisms (Pierrot et al., 2001; Gosselin et al., 1992b; Tsai, 1996).
Traveling along a pole or tubular structures with bends and branches requires four DOFs (two translations and two rotations along and perpendicular to the tubular axis). These same DOFs are also essential for most manipulation and repair tasks required in the pole climbing applications. More details on modeling of the mechanism and selection process of the planar parallel mechanism as the parallel part of the robot has been discussed in Vossoughi et al. (2004).
To the best knowledge of the authors, there is no four-DOF mechanism providing two translational and two rotational DOFs suitable for such operations. The mechanism proposed in this paper takes advantage of a parallel/serial mechanism providing two degrees of translation and two degrees of rotation along the desired axes (which will be described later). The parallel/serial robots also have the advantages of high rigidity of fully parallel manipulators and extended workspace of serial manipulators (Romdhane, 1999). Full kinematic analysis of the four-DOF mechanism has been presented completely in Zakerzadeh et al. (2004).
The mechanism also takes advantage of a novel gripper design, making it suitable for safe pole climbing operations.
Concept
As mentioned earlier, locomotion along tubular structures, with bends and branches, requires a minimum of four DOFs. These include Tz: a translational DOF for motion along the pole axis (Figure 1), Rz: a rotational DOF for rotation around the pole (Figure 2), Rx: a secondary rotational DOF for rotation around a radial direction of the pole (Figure 3).
Figure 1 Climbing along the pole
Figure 2 Rotation around the pole axis
Figure 3 Overtaking the bent section
Combination of the above three DOF with Tx a translational DOF for motion along the pole radial direction provides the necessary manipulability to perform the many necessary operations after reaching the target point on the pole (i.e. repair, maintenance or even manufacturing operations such as welding) (Figure 4).
The robot design
The proposed pole climbing robot consists of three main parts (Figure 5), the three-DOF planar parallel mechanism, the serial z-axis rotating mechanism and the grippers.
Combining the three-DOF planar parallel mechanism with a rotating mechanism around the pole axis provides two rotations and two translations, which is necessary to achieve the design objectives as explained in the last section.
Figure 4 Robot performing a welding operation
Figure 5 The pole climbing robot model
Furthermore, the linear cylinders used in the parallel manipulator are arranged to encircle the pole and thus reduce the grasp moments on the gripper.
One of the grippers is attached to a manipulator, and the other one is attached to the base of the rotating platform. As a result, the grippers have four DOF with respect to each other, allowing for movements along the poles with different cross- sections and geometric configurations.
The three-DOF planar three-RPR parallel three-RPR manipulator
A general planar three-legged platform with three DOFs consists of a moving platform connected to a fixed base by three simple kinematics chains. Each chain consists of three independent one DOF joints, one of which is active (Gosselin et al., 1992a). Hayes et al. (1999) showed that there are 1,653 distinct general planar three-legged platforms with three DOFs. For the proposed mechanism, the three-RPR mechanism has been selected as the planar parallel part of the robot.
The rotating mechanism
The rotating mechanism consists of a guide, a sliding unit, a gear set and a motor. Plate 1 shows the guide and sliding unit. The guide is a T-shape circular guide, which encircles the pole. The slider unit consists of a particular bearings arrangement, which can withstand the forces and torques generated during various maneuvers and maintains the robot stability in all its possible configurations. The slider holds the lower gripper and is driven by a motor with a simple gearing arrangement. By rotating the motor while keeping one of the grippers fixed (to the pole), the other gripper can rotate around the pole axis.
The grippers
The proposed gripper has a unique multi-fingered design, which is able to adapt to various pole cross sections and dimensions with only a single actuator. Each gripper consists of two v-shaped multi-fingered bodies, a double shaft motor, two right and left handed screws and two linear guides. Use of the particular multiple finger arrangement not only increases the torque handling capability of the gripper but also improves the adaptability of the gripper to different pole dimensions without having fingers interfere/collide with each other. Using ballscrews with a friction coefficient of 0.1, and two linear bearing which stand the load of the robot during the climbing process, the selected double shaft electric motor is rather small with respect to the weight of the robot. Plate 2 shows the fabricated gripper.
Plate 1 The serial rotating mechanism
Plate 2 The robot fabricated gripper
The combined actions of the various components in a typical pole climbing application are shown in Plates 3-5.
Table I shows the specifications of the prototype version
and the estimated specifications of the industrial version of robot.
The robot prototype
Following the kinematic analysis of the proposed mechanism (Vossoughi et al., 2004; Zakerzadeh et al., 2004), a prototype unit was designed and built for a hypothetical municipal light bulb change operation.
The prototype of the robot weighs 16 kg. The body of robot is fabricated from aluminum. The robot is driven by three dc motors and three electrical cylinders. Use of electrical cylinder rather than pneumatic or hydraulic cylinders simplifies the control of cylinders and increases the precision. Also there is no need for a compressor or pump. This also eliminates hydraulic or pneumatic tubes, which are not safe in pole climbing applications.
The electrical cylinders weigh 1.1 kg each. Each cylinder is able to exert a 800 N force and has a stroke of 200 mm and speed of 0.6 m/min.
Revolute joints in the planar parallel mechanism should be fabricated with a relatively high tolerance. Otherwise, the planar parallel mechanism will either be overconstrained or exhibit extra DOFs. In addition the assembly process precision is also highly important for the proper operation of the mechanism. To accommodate the light bulb change operations two miniature grippers have been used. One to carry the new lamp, and the other to remove the old lamp. The grippers are two small pneumatic grippers. Also a small reservoir with capacity of 300 cc has been used. A dome remote control camera has been attached to the manipulator to assist in the bulb changing operation using a joystick as the robot remote control teach pendent unit. The camera has two DOFs and can rotate around two perpendicular axes and is enveloped by a dome. Plate 6 shows the fabricated prototype.
Plate 7 shows the fabricated prototype moving along the pole axis, Plate 8 shows the fabricated prototype passing the bent section of pole and Plate 9 shows the fabricated prototype in the operation of light bulb changing.
Control of the robot
As mentioned earlier, the prototype unit is actuated by three electrical cylinders and three dc motors. Each motor has a control driver board, which is attached to a central PC.
Plate 3 The robot movement along pole axis
Plate 4 The robot rotation around pole axis
Plate 5 The robot is passing the bent section
Table I Estimated characteristic of the prototype version and the industrial version of robot
Number of linear actuators
Number of rotary actuators
Weight (kg)
Dimensions (cm)
Prototype
3
3
16
18 ￡ 25 ￡ 60
Industrial
3
3
30
50 ￡ 50 ￡ 100
Plate 6 The fabricated prototype
Plate 7 Moving of fabricated prototype along pole axis
Plate 8 The fabricated prototype is passing the bent section
The gripper motors are controlled using current feedback. Once the grippers touch the pole the current will increase to reach to a certain value thus exerting a proportional amount of force. Owing to the large gear ratio of the gripper’s dc motor the motor is not back-drivable. As a result in case of power failure, the gripper will continue to exert the force continuously, making it fail-safe in case of power failure.
The electrical cylinders comprise a dc motor, a gearing arrangement and an acme screw. Using a 500-pulse encoder
on the shaft of the dc motor, the cylinders have a precision of
0.1 mm in linear movements. Also using a 100-pulse encoder on the shaft of the serial rotating mechanism’s dc motor, the serial mechanism has a precision of 0.68 with the given gearing arrangement of the serial mechanism.
An array of touch switches, which have been assembled on the upper grippers, not only detect bend and other possible barriers on a pole, but also can detect the angle of a bent section of the pole with respect to the present direction of the robot gripper. This will allow the serial mechanism to rotate
Plate 9 The fabricated prototype in changing bulb operation
in a way that the robot mechanism is positioned properly for passing along the bent section.
The control system architecture includes a higher level
inverse kinematic module and a lower lever PID-based joint level position control system.
Conclusion
In this paper, a solution to the autonomous robot pole climbing problem is presented. A unique multi-fingered gripper with the ability to adapt to various poles cross sections and dimensions with only a single actuator is also presented. Then some of the issues concerning the prototyping and control of the robot mechanism are discussed.
References
Aracil, R., Saltare′ n, R. and Reinoso, O. (2003), “Parallel robots for autonomous climbing along tubular structures”, Robotics and Autonomous Systems, Vol. 42, pp. 125-34.
Gosselin, C.M., Sefrioui, J. and Richard, M.J. (1992a), “Polynominal solution to the direct kinematic problem of planar three degree of-freedom parallel manipulators”, Mechanism and Machines Theory, Vol. 27, pp. 107-19.
Gosselin, C.M. et al. (1992b), “On the direct kinematics of general spherical 3-degree-of-freedom parallel manipulators”, ASME Biennial Mechanisms Conference Proc., Scottsdale, AZ, pp. 7-11.
Hayes, M.J.D., Hysty, M.l. and Zsombor-Murray, P.J. (1999), “Solving the forward kinematics of a planar three-legged platform with holonomic higher pairs”, ASME J. Mech, Vol. 121, pp. 212-9.
Merlet, J-P. (2000), Parallel Robots, Kluwer, Dordrecht. Pierrot, F., Marquet, F., Company, O. and Gil, T. (2001),
“H4 parallel robot: modeling, design and preliminary experiments”, ICRA, pp. 3256-61.
Romdhane, L. (1999), “Design and analysis of a hybrid serial parallel manipulator”, Mechanism and Machine Theory, Vol. 34, pp. 1037-55.
Salataren, R., Aracil, R., Sabater, J.M., Reinoso, O. and Jimenez, L.M. (1999), “Modeling, simulation and conception of parallel climbing robots for construction and service”, paper presented at the 2nd International Conference on Climbing and Walking Robots, pp. 253-65.
To¨ nshoff, H.K. (1998), “A systematic comparison of parallel kinematics”, Keynote in Proceedings of the First Forum on Parallel Kinematic Machines, Milan, Italy, 31 August-1 September.
Tsai, L.W. (1996), “Kinematics of a three-dof platform with three extensible limbs”, Recent Advances in Robot Kinematics, Kluwer, Dordrecht, pp. 401-10.
Vossoughi, G.R., Bagheri, S., Tavakoli, M., Zakerzadeh, M.R. and Houseinzadeh, M. (2004), “Design, modeling and kinematics analysis of a novel serial/parallel pole climbing and manipulating robot”, paper presented at the 7th Biennial ASME Engineering Systems Design and Analysis conference, Manchester, 19-22 July.
Zakerzadeh, M.R., Vosoughi, G.R., Bagheri, S., Tavakoli, M. and Salarieh, H. (2004), “Kinematics analysis of a new 4- DOF hybrid (Serial-Parallel) manipulator for pole climbing robot”, paper presented at the 12th Mediterranean Conference on Control and Automation.