ROBOTLAB: A SOFTWARE FOR ROBOT GRAPHIC SIMULATION Narpat s. Gehlot Universidade Federal da Paraíba - Departamento de Engenharia Elétrica 58109 - 970 Campina Grande-PB-Brasil E-mail:
[email protected]
Pablo J. Alsina Universidade Estadual da Paraíba - CCT - Departamento de Física 58100-000 Campina Grande - PB - Brasil
Abstract: The ROBOTLAB is a MATLAB based software package developed for robot simulation and analysis. MATLAB users can analyze and simulate any arbitrary serial link manipulator using ROBOTLAB by specifying robot kinematics, geometric and dynamic parameters. The package incorporates an extensive library of functions of transforrnations, kinematics, dynamics, control, trajectory and 3D animation of robots . IIIustrative examples are presented to show the capability of the ROBOTLAB.
1. INTRODUCTION
The availability of powerful software packages such as Mathematica, MATLAB and MAPLE, has motivated the development of software tools for the analysis and simulation of robotic systerns (Nethery & Spong, 1994; Corke, 1996). Also, for Unix operating systems a robot graphic simulator (Marhefka & Orin, 1996) has been developed which is portable over wide range of platforrns . The use of software based tools for the simulation and analysis of robotics systems provides a very attractive solution of design problems & is ideal for educational purposes, since the cost of experimental setups is generally high. Moreover, the flexibility of the software tools perrnits convenient training and teaching aids (White, et al., 1989) as well as allows the investigation of control strategies without the need of an experimental prototype (McMillan, et aI., 1995; Agba, 1995). In this paper, the ROBOTLAB: A Graphic Robot Laboratory Simulator (Alsina, 1996) is described which consists of a versatile robotics functions library , interactive graphic user interfaces and forceful 3D animation tools . ROBOTLAB was developed for personal computers, running MATLAB 4.0 in Windows . Given an appropriate description file of any arbitrary N-link
serial robot, the ROBOTLAB functions, like MATLAB functions, are used in the analysis, dynamics simulation and 3D animation to create a Virtual Prototype. ROBOTLAB user interface is described in Section 2. In Section 3, robot modeling commands are discussed . Section 4 presents a general description of the RüBOTLAB environment, including details of the different program modules and graphic output interface. An iIIustrative example is given in Section 5 to show the versatility of the package. A comparison with other state-of-the-art packages is given in Section 6. 2. ROBOTLAB USER INTERFACE
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ROBOTLAB is an interactive environment for robot analysis , dynamic simulation and graphic 3D animation. ROBOTLAB front end is a friendly graphical user Interface, developed in MATLAB, which provides an easy way of executing the ROBOTLAB tasks. The ROBOTLAB command functions (see Table I) are norrnally transparent to. the user and are utilized for writing RÇ)BOTLAB user programs. Figure 1 shows an example of the Graphic user interface.
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variables : one for the forrn and size and other for the reiative positioning of the part in the link . The first variable foIlows the forrnat: PL , where is a two-digit number associated to the part and is a two-digit number associated to the corresponding link. This var iabIe must be initialized by means of an appropriate graphic primitive function in order to store the forrn and size of the corresponding part oThe second variable defines the relative positioning of the part with respect to the link reference frame by means of a homogeneous transformation. The general format of this variable is TPL, where and were defined above. For example, the part 3 of link 4 could be created as:
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Fig. 1 - ROBOTLAB Menu .
P03L04 = [2
3. ROBOT MODELING
0.5]
TP03L04 = [ I O O O
Any serial robotics manipulator can be simulated in ROBOTLAB. The manipulator is specified by the user by a proper parameter file in the format MATLAB "script-file". This file includes the kinematics, dynamics and geometric parameters of a robot to be simulated. The input data (from files or keyboard) is written in the MATLAB language forrnat: matrix between brackets, elements in a row separated by blank spaces and each row separated by a semicolon. The kinematics parameters are given in a matrix named KINPAR. Each one ofthe N rows of matrix KINPAR consists of tive elements that describe completely the kinematics of one link: the type of joint and the four Denavit-Hartenbeg parameters (ai, ai, di, ai) (Craig, 1986). For example, for single-link system with a rotational joint, the cinematic parameters.are specified as:
O 1 O O
O O 1 O
5 O O 1];
The numb er 2 in part P03L04 is a code for a hemispheric part and 0.5 is the radius length . The variable TP03L04 indicates that the hemispheric part is aligned with the reference frame ofthe link 4 (rotation matrix equal to identity matrix) and its center is localized 5 units in the positiv e direction of the x-axis of the frame . Using the geometri c modeling form given above, user can specify any robot of desired structural detai ls. Figur e 2 shows an example ofrobot manipul ator geometric modeling. 1, 0.8
N
0.4
Similarly, the dynamics parameters are given in an N row matrix named DYNPAR. Each row includes the mass (m.), vector of center of mass (S = [S, S, Sz]T), inertia tensor elements n, = n, Iyy I,z]T and I, = [Iyz .Ixz Ixy]T), Coulomb friction coefficient (Ac) and viscous friction coefficient (Av) of.one link. For example, for single-link ' system with a rotational joint, the dynamic parameters are specified as:
0.2
0.5
o Y(m)
-o.
-0.5 X(m)
Fig. 2 - Example ofrobot geometric modelin g.
The geometric model of the robot is\ composed by links, which are numbered sequentially, starting from the base of the manipulator. Each link is Cõmposed by several numbered parts (graphic objects), which are created using some special graphic primitive functions (prism, cone, cylinder, sphere, hemisphere). Each part is specified by two
4. THE
PROGRAM
4. J General Characteristics ROBOTLAB is structured in several module s, which can be expanded accordin g to the user needs . ROBOTLAB is divided: in . six main modules :
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Homogeneous Transfonns, Trajectory Generation, Kinematics, Dynamics, Graphics and Dynamics Simulation. Each module consists of a set of MATLAB functions, developed for each specific problêrn, and, due to the open structure, they can be utilized by the user in his own programs. A list of the available ROBOTLAB functions is given in Table I.