Development of a Wall Climbing Robot
with Wheel-Leg Hybrid Locomotion Mechanism *
Yili Fu, Zhihai Li, Hejin Yang and Shuguo Wang
Robotics Institute
Harbin Institute of Technology Harbin, Heilongjiang Province, China
*
This work is supported by National Natural Science Foundation of China under Grant 60675051.
Abstract - A novel prot ot ype of lf-cont ained wall-climbing robo t ud for special t asks such as rescue, inspec t ion, surveillance and reconnaissance is developed. The wheel-leg hybrid locomotion mechanism enable the robot to achieve quick mot ion on wall surface, as well as obst acle- spanning on wall surfaces and smoo t h wall-t o-wall t ransi t ions. The robo t is compod of a ba body and a
mechanical leg wit h 3 DOF. The ba body is a big flat suction cup with three-wheeled locomotion mechanism inside, and there is a small flat sucker in t he end of t he mechanical leg. The new designed chamber al has simple structure and has steady and reliable performance. A distributed embedded cont rol syst em is also described which enable t he robo opera ing manually and mi-au onomously in wheeled mot ion mode or legged mot ion mode. Kinemat ics model of t he robot is est ablished t o analyze t he robot 's mot ion on t he wall. And the locomotion gait of the robot is discusd. Safety analysis of he robo on ver ical surfaces shows he robo ’s reliable adhesion ability to working on wall surfaces.
Index Terms –Wall Climbing Robot, Vacuum Adhesion, wheel-leg hybrid locomotion mechanism, distributed embedded control system
I. I NTRODUCTION
In rent years, mobile robots ud for special tasks such as rescue, inspection, surveillance and reconnaissance have been studied hotly. For example, Urban robot from iRobot, Inc, US [1], Teodor from Telerob, Germany [2], Cyclops from AB Precision, UK [3], and so on. The robots can work instead of people to execute dangerous tasks in hazardous environments, such as disposal of explo
sive ordnances. But they are absorbed in working in horizontal terrains, and have no ability to work in vertical surfaces. Otherwi, wall-climbing robots which can climb and move on vertical surfaces can breach this limitation. They can give people more help in vertical surfaces like outer wall surfaces of high structures to execute hazardous missions. The dangerous tasks demand the robot have small volume, low weight, excellent mobility and maneuverability. But the technologies ud in the previous wall-climb robots cannot meet the need of the new special tasks. Wall-climbing robots that have been developed are always ud in industries, for example, maintaining nuclear facilities, inspection of stage tanks, cleaning high-ri building, painting, and so on [4-11]. They always have big body, high weight, and low agility. So, new prototypes of lf-contained wall-climbing robot need to be developed to execute the special tasks [12-14].
Here, a new type of wall-climbing robot is propod, which integrates the advantages of wheeled robots and legged robots. It can achieve quick motion as well as obstacle- spanning on wall surfaces, and even smooth wall-to-wall transition by applying wheel-leg hybrid locomotion mechanism. Vacuum bad adhesion mechanism is ud to adapt to versatile surfaces.
In ction I, a brief introduction is given. In ction II, mechanical design of the robot is prent. In ction III, movement on wall surfaces is analyzed, and safety of the robot is discusd. In ction IV,
robot’s control system is introduced. And in ction V, conclusions are made and future works are prospected.
II. D ESIGN P RINCIPLE AND C HARACTERISTICS OF R OBOT
D esign requirement for mobile robot working on wall surface for anti-terrorism and reconnaissance tasks mainly include: 1) Omni-directional movement. 2) High mobility. Maximum velocity of the robot is 10
m/s. Having ability to transit between different surfaces, and step over obstacles. 3) Be attached to surface reliably. 4) Can working on wall surfaces with ordinary materials. 5) Be a lf-contained system.
心中的太阳作文Adhesion mechanisms ud in the past mainly include magnetic devices, vacuum adhesion technique, propeller forces and even dry adhesion materials [4,18,19]. In order to enable the robot to adapt to versatile surfaces, negative air
pressure adhesion technique is chon, becau this method can suit walls such as ceramic tile, glass, cement and brick walls [13-17]. Locomotion mechanism is a key point of wall climbing robot.
There are many reprentative locomotion mechanisms. NINJA developed by Tokyo Institute of Technology adopts four-leg locomotion mechanism with vacuum cups in the feet. Each leg is a 3-dof parallel mechanism. Its moving speed is 1
m/s [11]. ROBUG II, developed by Portsmouth Polytechnic has four 3-dof biological limbs [12]. Biped robot designed by Michigan State University has four rotational joints, using under-actuated kinematic structure [14]. And single cup wall Proceedings of the 2007 IEEE
International Conference on Robotics and Biomimetics
December 15 -18, 2007, Sanya, China
climbing robot developed by City College of New York us three-wheel mechanism, and speed of the robot is 10 m/min [15].
Considering needs of anti-terrorism and reconnaissance tasks, a hybrid locomotion mechanism is developed for this robot. As shown in fig.1. The mechanism enable the robot to be able to move with high speed as well as step over obstacles such as protuberances, gaps. The novel wall-climbing robot is shown as Fig. 1.
Fig. 1. Outlook of the novel wall climbing robot
III.M ECHANICAL D ESIGN AND K INEMATICS OF THE R OBOT
Design of the locomotion mechanism is interrelated with the design of adhesion mechanism. The robot adopts vacuum adhesion to stick the robot to vertical surfaces. Movement of the locomotion mechanism is realized under the reliable adhesion of the robot on surfaces. The wheel-leg hybrid locomotion mechanism consists of a wheeled mechanism and a climbing mechanism.
Considering that the wheeled locomotion mechanism should work with the robot’s sticking on surface. So that a big vacuum suction cup is ud, which can attach the robot to vertical surfaces along with the robot’s moving. And the big sucker is also ud as frame of the robot. The wheeled locomotion mechanism is fixed inside the big vacuum sucker, working as the ba mobile body of this novel wall climbing robot. 3-wheel mechanism with two drive wheels and a castor wheel is ud, becau of its advantage in moving stability. It can avoid shaking like 2-wheel mechanism.
The climbing mechanism is inspired by biped wall-climbing robot. There are always two suckers equipped in each foot for biped robot. In order to realize biped robot’s moving forwards, backwards, and turning movements, they always have no less than four D egree of Freedom. Here, the wheeled locomotion mechanism has the ability to turn the orientation of the robot, so that the climbing mechanism only needs to have three D OF. Assignment of the wheeled locomotion mechanism is to drive robot to realize omni-orientation movement. On the other hand, assignment of the climbing me
chanism is to step over obstacles. The two mechanisms are integrated as shown in Fig. 2.
The climbing mechanism is compod of two rotational joints and one translational joint. The translational joint is realized by rack and pinion mechanism driven by a DC motor.
Fig. 2. Construction of the hybrid locomotion mechanism
D esign of the flexible aling skirt could guarantee the aling of vacuum chamber inside the big sucker while wheeled mechanism is moving. On the other hand, smooth
fabric outside the aling skirt has small friction with surfaces,
which could reduce energy consumption of the robot.
Specifications of the robot are shown in TABLE I.
TABLE I
S PECIFICATIONS OF THE R OBOT
Parameters value
unit Mass 9.5
网络改变世界Kg Size of ba body 300×300×85 mm
Size of small sucker 150×450×3 mm
Speed of wheeled mechanism 10 m/min
Speed of legged mechanism
什么学历可以考公务员(time to step over a ledge)
< 12 s
Load capacity of big sucker 40 Kg
Load capacity of small sucker 30 Kg
In order to facilitate the analysis of robot’s movement, relationship between joint variables and the robot’s position/orientation should be establish.
Considering that the wheel mechanism can move in 2D
terrain with the movements-move forwards, move backwards,
turn left, turn right, and turn with zero radius, the position and orientation of the robot’s body is determined by the 3-wheel mechanism. The 3-wheel mechanism has two joint variables-rotational angles of the two driving wheels. As shown in Fig.3, coordinate of the robot’s ba body is established in the
Fig. 3 Coordinates frames of Fig. 4 Coordinates frames of
the ba body the mechanical leg
center of the two driving wheels’ axis. Position/orientation of
the robot’s ba body can be expresd by (x,y,ș)T, which is
shown as (1).
112()2x r y J ,L φθφθªºªº«»=«»«»¬¼«»¬¼
(1) 1cos cos ()sin sin 1/1/J ,L L L θθθθθªº
«»=«»
«»−¬¼
Where, ӿ and ӿ denote the two driving motors’ rotational angle respectively.
Becau the movement of climbing mechanism is to reali climbing movement in 2D plan, so that kinematics of the climbing mechanism only needs to analysis the relationship between the foot of climbing leg and the ba body. And the relationship could be expresd by the position/orientation of the foot to the ba body, which is expresd by (x03,y03,ij03)T, as in (2). Assignment of coordinate frames is illustrated in Fig.4. The link parameters are shown in Table II. ș1, d2, and ș3 are joint variables, and a1 reprents length of link3, a3 reprent length of link1.
TABLE II
Link Coordinate Parameters of the Mechanical Leg.
外国小说推荐Joint și /° d i /mm a i /mm Įi /°
Range of joint
variable
Joint1 ș1 0 a 1=20 -90 ș1==0~360° Joint2 0 d 2 0 90 d 2=72~467 mm Joint3 ș3 0 a 3=95 0 ș3=-57°~237°
031121313cos sin sin()x a d a θθθθ=−−+
031121313sin
cos cos()y a d a θθθθ=+++ (2) 0313/2ϕθ绝句译文
θπ=+−
IV. R OBOT ’S M OVEMENT
The hybrid locomotion mechanism enables the robot to have two motion modes: wheeled motion mode and legged motion mode, which improves the robot’s mobility evidently.
The wheeled locomotion mechanism is ud to realize high speed movement. And legged mechanism is ud to span obstacles. Robot’s movements on wall surfaces mainly include: moving upwards, moving downwards, turning, transition to the other surface, spanning obstacles, and so on.
Among the movements, moving upwards and down wards can be realized by wheeled mechanism or climbing mechanism; turning movement is conducted by wheeled mechanism, by controlling the two driving wheels in differential way; transition movement between surfaces and obstacle-spanning movements is realized by climbing mechanism.
Obstacle-spanning movement of the robot can be divided into two conditions, 1) span protrude 2) span gap. As shown in Fig. 5, the movement quence to span a ledge can be divided into four periods: 1) The robot gets clo to the ledge, as Fig. 5.1); 2) extend the mechanical leg to drive it over the ledge, and let the flat sucker in the foot stick on surface, as shown in Fig. 5.2);
3)
lift the ba body over the ledge, as shown in
Fig.5.3,4); 4) ba body lands on surface, relea and retract the climbing leg, as Fig. 5.5).
1) 2) 3) 4) 5)
Fig. 5. Robot’s movement quence to span a ledge
Transition from floor to wall is realized by a quence of movements illustrated in Fig. 6. The quence can also be divided into four periods:
1) The robot gets clo to wall surface and keep a certain distance with it, as shown in Fig. 6.1);
二年级语文书2) extend the mechanical leg to place the foot on wall surface , and let the flat sucker in the foot stick on surface, as shown in Fig. 6.2);
3) lift the ba body onto wall surface, as shown in Fig.6.3);
4) land ba body on vertical surface, and let it stick to surface, then relea the climbing leg, as shown in Fig. 6.4).
1) 2) 3) 4)
Fig. 6. Robot’s movement quence to transit from ground to vertical surface
The moving ability of the robot is determined by structure and parameters of the locomotion mechanism. It mainly includes: turn ability of the wheels mechanism and obstacle-spanning ability. The differential driving mechanism of the ba body enables the robot to have enough mobility in sm
ooth surfaces. Obstacles-spanning ability is determined by the parameters of the climbing mechanism.
Protrudes on wall surface always take on different shapes in ction, but they could be predigested into a unique shape rectangle. So the obstacle-spanning ability of the climbing mechanism could be expresd by the width and height of biggest obstacles that it can step over. Width and height of the obstacle can be calculated by (3),
ker 12
suc obstacle L
w W =−−
11obstacle h H W =+ (3)
Where, w obstacle reprents width of ledge; h obastacle reprents height of ledge; H 1 is the height of joint 1; W 1 is the distance from axis of joint 1 to front of ba body; and L sucker is the length of the small sucker.
V. S AFETY A NALYSIS OF R OBOT ON S URFACES
Safety of the robot when it works on wall surfaces is influenced by working environments. For example, water, dust on surface can monish friction between robot and surface, extra load that go beyond load capacity of robot can result in dropping of robot. Failure of the robot’s sticking on wall surface mainly has two ways: slip down and overturn form surface. So the safety analysis should be conducted in the two ways. And in the wheeled motion mode and legged motion mode, force condition of the robot is different. So that safety analysis is conducted respectively in the two modes.
A. wheeled motion mode
Fig. 7.1) shows the forces acting on robot when it works in wheeled motion mode. Where, F p denotes adhesion force, f 1l and f 1r reprent friction force between the two driving wheels and surface, and f 2 reprents friction force on the castor, and G denotes gravity. If the robot didn’t slip down from surface, there should be sufficient friction force between robot and surface.
朦胧的胧组词()A
B
C
f f f G +−≥ (4)
Where,11max A B NA NA f f F F μμ==≤<< (5)
22max C NC NC f F F μμ=≤<< (6)
From (4),(5) and (6), the needed adhesion force F p is given by,
p underside F H G ≥<, ()()12122underside l h
H l
μμμμ−+=−<< (7)
In order to avoid robot’s overturning from wall surface, the robot needs to have enough counter-overturning moment. When robot sticks on wall surface without overturning, there is,
()0,20p NC M B F l F l G h =−−=¦<<<, and 0NC F ≥ (8) From (8), it could be got that,
/p F G h l ≥< (9)
1) wheeled mode 2) legged mode
Fig. 7. Forces acting on robot in wheeled mode
and legged mode
B.
legged motion mode
Fig. 7.2) shows the condition when robot works in legged motion mode. If the robot didn’t slip down from surface, the load force F y on the flat sucker should satisfy (10)
()00L
y N n L l dl F μ+−≥ªº¬¼³<<< (10)
Where, N 0 denotes normal force on the front point of the flat sucker, n denotes density of normal force, and μ reprents friction coefficient.
And relationship between the normal force acting on robot and vacuum force F p is as shown by (1
1).
()00
L
p N n L l dl F +−=ªº¬¼³
<< (11)
From (10) and (11), it can be got that,
max y p F F μ≤< (12)
If the robot didn’t overturn from surface, there is,
()0,20p NC M B F l F l G h =−−=¦<<<, and 00N ≥ (13) From (13), the overturning moment T generated by load should be calculated by,
6
p y y F L
T F H =≤<< (14)
The overturn moment of the robot when the climbing mechanism lifts the ba body over obstacle can be calculated by (15).
i i T H G =¦< (15)
Where, H i is the distance between center of part’s mass of the robot and wall surface. G i is the gravity of each part.
When the robot move on vertical surfaces in wheeled motion mode, the gravity of robot is constant, so (7) and (9) could be satisfied by guarantee F P in safety range. From experiment in practice, load capacity of the big sucker is measured as shown in TABLE I.
When the robot steps over a ledge in legged motion mode as shown in Fig. 5, load force F y is constant, which include robot’s gravity and its load. It is shown in TABLE I. In (14), overturn torque T is changing when robot is moving. Fig. 8 shows the result from the simulation of robot’s obstacle-spanning movement conducted by ADAMS. The three curves show the distance from surface of each part’s centroid. From Fig.8, it could be calculated that the maximal overturn moment is about 11.738 Nm.
max 11.78i i T H G Nm ==¦<
Time (s)
西游记第一回读书笔记Fig. 8. Distance between centroid and wall surface when the climbing leg lift
ba body over a ledge
When vacuum degree inside small sucker is 20 KPa,
P o s i t i o n o f c e n t r o i d (m m )
33.7566
p F L
P L W L
T Nm Δ<==<<<<
So the robot could keep sticking on vertical surface reliably among robot’s spanning movement.
VI. C ONTROL S YSTEM
Control system of the robot is compod of controllers on
the robot and remote control station on the ground, as shown
in Fig. 9. Communication between them relies on wireless
communication module. In order to be convenient for design,
maintenance, and expanding of the control system, a
distributed control system is designed, which include: center controller, wheel controller, leg controller, nsors suit, and battery module. Modular design of the control system is convenient for the respective control of wheel mechanism and
leg mechanism. Center controller can exchange data via
RS485 protocol with the child controllers including control commands and state information of robot.
Fig. 9. Control system block diagram
High performance MCU-ATmega128 from ATMEL which have high speed performance, large volume on-board program and data memories, is very suitable for embedded control system. So it is lected as the core of every controller module.
Center controller with ATmega128 as core is assumed to control the other modules on the robot to realize robot’s movements. It exchanges data including commands and information with the remote control station on ground via wireless data module STR30.
Bad on modules design principle, a driving control module for multi DC motors is designed, which can be ud for both wheeled mechanism and legged mechanism. Construction of the multi-motor control module is shown in Fig. 10. ATmega128 is the core of the model, and there are three uniform modules that consist of LM629, LMD 18200. Each model is ud to control one motor respectively.
Precision motion controller LM629 receives command from ATmega128 and generates PWM signal to drive DC motor via
H-bridge LMD 18200 in speed or position mode. Incremental encoders equipped on the motors are u
d to form a clo loop. ATmega128 controls the three control models in proper way according trajectory of wheels or climbing leg to realize the needed trajectory.
Control of the robot needs to detect condition information of the robot and environments around it, so some nsors are
equipped on the robot. In order to obtain real-time orientation
of the robot when it moves on wall surface, a 2-axis
inclination nsor is ud, which can realize angle
measurement in the range of 360°. Two pressure nsors are
ud to detect the pressure inside the vacuum suckers. Besides,
infrared nsors are ud to detected obstacles in the environments.
Fig. 10. Structure of multi-motor control module
The robot can be operated both manually by telecontrol and mi-autonomously. According the com
mand received from remote controller, the robot can be controlled in wheeled motion mode or legged motion mode. As shown in Fig. 9, the remote control station on the
ground which is a PC, gives commands to the center controller on the robot, for example move forwards, turn right, step over
a ledge, step over a gap and so on. The center controller interprets the commands, and reads data from nsor system to obtain status messages of its lf and information about environment. Then task level planner in center controller generates task commands that robot should conducted. Bad
on the task commands, trajectory planner in center controller generates a t of desired joint values for the robot’s locomotion mechanism. The joint data is transferred to wheel controller or leg controller via RS485 protocol according to control commands, to drive the motors to realize
robot’s movements. The assignment that wheeled mechanism and legged mechanism are controlled by two control module respectively is helpful for the realization of wheeled motion mode and legged motion mode, and enhances reliability of the two motion mode. VII. C ONCLUSION
The novel wall-climbing robot prented in the paper can realize agile movement on vertical surface with the wheel-leg
