COOPERATIVE MODELING AND DYNAMICS SIMULATION

OF FLEXIBLE MULTI-BODY SYSTEM FOR PARALLEL ROBOT

Yongxian Liu

, Chunxia Zhu

and Jinfu Zhao

School of Mechanical Engineering and Automation, Northeastern University, Shenyang, China

Liaoning Energy Key Project Investment, Limited Liability Company, Beiling Street, Huanggu District, Shenyang, China

Keywords: Parallel robot, Dynamics of flexible multi-body, Cooperative, Modeling, Simulation, ADAMS, ANSYS.

Abstract: Based on the cooperative thought, a method of modeling and simulation of multi-flexible-body dynamics

for a kind of mechanism is proposed in this paper. A multi-flexible-body dynamics simulation model of 3-

TPT parallel robot is created, and its multi-body dynamics simulation is implemented by using the multi-

body dynamics simulation software ADAMS and finite element analysis software ANSYS. For more

accurate explanation of the analysis, simulation results of rigid body are compared with those of flexible

body. The simulation results have shown that forces applied on flexible bodies are highly nonlinear because

of the flexible characteristics, which is consistent with the reality. Compared with other simulation method,

the simulation proposed of the multi-flexible body system are more authentic, nicety and can reflect actual

dynamics characteristic of parallel robot with more accuracy. Therefore this is an effective method of

analysis for design and optimization of parallel robot.

1 INTRODUCTION

Flexible multi-body system generally consists of

rigid body and flexible body which interact with

each other the motion of these components unit may

be translational or rotational under the effect of

power. The traditional multi-body system dynamics

research is carried out mainly in the multi-rigid-body

field, however, because of the rigid assumption

sometimes its result will lose certain precision, even

can't be accepted (Shabana A. A, 1997). With

development of modern mechanical system towards

to high speed, heavy load, high-precision direction,

designers pay more and more attention to dynamic

stress of the component and the service life

prediction of product, elastic dynamics issue

resulting from the coupling between rigid motion

and the deformation itself of the system has already

become the common problems needed to be resolved

and key technology in this field. Therefore

considering the flexible of all the parts in order to

improve the precision of the simulation analysis

becomes an important direction of parallel robot

research (Fattah et al., 1995; Gamarra, 1999).

Robot dynamics simulation analysis is an

important content of robot design, the model

established in the previous analysis, whose

components belong to a rigid body, and don’t have

elastic deformation when making motion analysis.

But in fact, on the condition of the larger load, or

acceleration and deceleration, it will have larger

deformation and displacement after the mechanism

got forced, resulting in vibration. In order to solve

these problems, we should establish the reasonable

elastic dynamics model of the parallel robot, based

on this research the impact of its dynamic

performance and structure and geometrical

parameters on dynamic properties, put forward the

corresponding structure optimization design method

(Chen, 2001).

ADAMS software is well-known mechanical

system dynamics simulation software, its analysis

object is basically the multi-rigid-body, but the

ADAMS provides a flexible body module, the

module can be used to achieve motion simulation

analysis of flexible body and substitute elastic body

for rigid body. ANSYS software is a universal finite

element analysis software, with a friendly cross-

section before and after the treatment, accurate and

efficient solver, has been widely used in various

fields, it can effectively integrated the finite element

analysis with CAD, CAE organically. In this paper,

combining advantages of two kinds of software, the

flexible multi-body system is established to conduct

321

Liu Y., Zhu C. and Zhao J..

COOPERATIVE MODELING AND DYNAMICS SIMULATION OF FLEXIBLE MULTI-BODY SYSTEM FOR PARALLEL ROBOT.

DOI: 10.5220/0003566303210324

In Proceedings of the 8th International Conference on Informatics in Control, Automation and Robotics (ICINCO-2011), pages 321-324

ISBN: 978-989-8425-75-1

 2011 SCITEPRESS (Science and Technology Publications, Lda.)

dynamic simulation of mechanism the dynamic

behavior of mechanism can be simulated more

realistically.

2 THE ESTABLISHMENT OF

FLEXIBLE MULTI-BODY

DYNAMICS MODEL OF

PARALLEL ROBOT

All the objects in the mechanical dynamics

simulation software ADAMS are defined as rigid

bodies, and its theoretical basis is multi-rigid body

dynamics, so the impact of structural flexibility

movement is ignored, which is not good enough for

many system dynamics analysis (Wang et al., 2005).

However the general finite element software can do

nothing for dynamic analysis of the movement

system containing large displacement. But in the

ADAMS, combination of rigid and flexible body can

be a more feasible solution which can simulate the

dynamic behavior of the mechanism movement

more realistically. The flow chart of multi-flexible-

body system collaborative simulation is shown in

Figure 1:

Figure 1: The flowchart of multi-flexible-body model

cooperation simulation.

2.1 The Establishment of Solid Model

of Parallel Robot

Because of this low-DOF parallel robot having

complex structure, while in the ADAMS modeling

of complex shape parts is not powerful enough,

when establishing robot models, in this paper, three-

dimensional CAD software SOLIDWORKS is

applied, because it has a seamless connection

between ADAMS and SOLIDWORKS. Therefore,

the function of model conversion between them is

used in this paper, in that the robot's three-

dimensional model is first imported into the

ADAMS, creating a virtual prototype model of the

robot. Obtained multi-body dynamics model of the

parallel robot in ADAMS through proper handling is

shown in Figure 2:

Figure 2: The multi-body model of parallel robot in

ADAMS.

2.2 Generation of Modal Neutral File

The principle of creating flexible multi-body

dynamics is applied for components for slender and

with lower stiffness generate flexible body parts,

while for large rigidity parts rigid body model can be

used. Therefore, only three flexible telescopic arms

were processed with flexibility and the other

components are rigid body. After the multi-body

dynamic model of the parallel robot is established in

the ADAMS, the telescopic arms of parallel robot is

needed to make discretization processing of finite

element in finite element software ANSYS, in order

to generate modal neutral document for multi-

flexible-body dynamics analysis purposes.

First, the telescopic arms parts of parallel robot

in three-dimensional solid software is saved solely to

generate Parasolid model neutral file, and then

ANSYS through a dedicated interface to read the

neutral file, the definition of units, real constant, and

materials etc. is completed. The divided cell grid, the

definition of the external nodes, before outputting

MNF-neutral file, must carry out quality, and load

etc. inspection operation to ensure that the reliability

of data is contained by the file of modal neutral file

of flexible telescopic arms in the ANSYS. After

meshing, finite element model of telescopic arms is

generated, which is shown in the following figure 3.

2.3 The Establishment of Flexible

Multi-body Dynamic Model

After parallel robot modal neutral file is established,

ADAMS / Flex Module is embedded in the

ADAMS. Through the Flex body to rigid dialog box

ICINCO 2011 - 8th International Conference on Informatics in Control, Automation and Robotics

322

Figure 3: The finite element model of mechanical arm in

ANSYS.

(a) The end effector velocity diagram of multi-rigid-body.

(b) The end effector velocity diagram of multi-flexible-body.

Figure 4: The end effector velocity comparison of multi-

rigid-body and multi-flexible-body.

under this module, the flexible body model is

imported into the ADAMS to replace the original

rigid body, thus parallel robot flexible multi-body

simulation model is obtained, and then through

model checking, multi-flexible-body dynamic

analysis can be carried out.

3 SIMULATION RESULTS AND

ANALYSIS

In order to carry out parallel robot dynamics

simulation analysis, 1000N acting force is applied

on the end effecter of built parallel robot along the X

negative direction, and dynamic characteristic curve

of multi-rigid-body model is compared with

dynamic characteristic curve of multi-flexible-body

in this paper. The comparison of end effector

velocity of multi-rigid-body and multi-flexible-body

is shown in figure 4. The contrast between force

curves of rigid and flexible driven link is shown in

Fig. 5.

(a) The rigid body.

(b) The flexible body.

Figure 5: The component force contrast between rigid and

flexible driven link along three direction.

From the above figures of the simulation results

we can see that: (1) Due to the existence of

mechanism clearance, Multi-rigid-body model has

vibration phenomenon before movement speed is

constant, while multi-flexible-body model reduces

the vibration due to the deformation of flexible

body, making the change of the speed more smooth.;

(2) The stress variation amplitude of rigid arm is

smaller and with good linearity, while the stress

variation amplitude of flexible arm is larger and

shows a highly nonlinear.

4 CONCLUSIONS

The motion characteristics of parallel robot flexible

multi-body system is studied based on co-modeling

ideas. In this paper, the combination of the finite

element software ANSYS and multi-body analysis

software ADAMS are successfully utilized for

COOPERATIVE MODELING AND DYNAMICS SIMULATION OF FLEXIBLE MULTI-BODY SYSTEM FOR

PARALLEL ROBOT

323

simulation. analysis of the parallel robot flexible

multi-body system. We have found that using

ADAMS and ANSYS co-simulation analysis of the

flexible system, the actual motion characteristics of

flexible system can be more realistically and

accurately. Since simulation model is easy to learn

with component flexibility, it is easy to observe the

deformation of the components, predict system

performance with more accuracy, and therefore this

method offers reference for improving and

optimizing the structure of parallel robot. Some

components of the system considered as flexible

body and assembled together with other components

to build dynamic analysis model of rigid-flexible

coupling is a worthful method for the field of

parallel robot research.

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