Simulation of kinematics functionality and design optimisation of an autocentrated gripping system.

Enciu, George ; Nicolescu, Adrian ; Dobrescu, Tiberiu 等

1. INTRODUCTION

The paper presents the achievements in the optimisation domain for the design for one effector for the manipulation and transport of the hoop type parts inside of a flexible manufacturing cell. The studied effector is a double effector, which allows the simultaneous manipulation of two parts.

The parts are transported by a gantry robot from a storage system to the automatic gripping system on the machine. The gripping of each part is done on the inner circular surface, with the auto-centred system with three bolts, symmetrically positioned with radial displacement (Nicolescu, 2009).

The hoop type parts have the mass of a maximum 10 kg and the inner diameter between the values: minimum 200 mm and maximum 400 mm, and the gantry robot is integrated as a supplying system inside of a flexible manufacturing cell endowed with machining centres for turning operations.

In Figure 1 a) are presented the component elements of the assembly: 1--the gripping system, 2--gripping blots, 3--machining centre for turning operations, 4--gantry robot.

In Figure 2 b) are represented the gripping system (1) and the gripping bolts (2).

2. DESCRIPTION OF THE STUDIED ASSEMBLY AND FUNCTIONAL COMPONENTS

For this study there were designed and modelled all the component elements of the effector (1--the cam, 2--the push rod driven by the pneumatic drive, 3--the push rod with spring, 4--the gripping bolts, 5--the maximum dimension of the disc part, 6-pneumatic drive), using the working environment CATIA V5 R16, and for the analysis with the finite elements method for the stress and deformations cases of the partial assembly, push rod-cam, it was used the working environment ANSYS.

In Figure 2 it is presented one of the two pneumatic drivers for driving the effector, which corresponds to the driving of a single gripping system. The gripping system is in the opened position; the maximum rotation angle of the cam is of 18[degrees], and the circle described by the three bolts has a minimum diameter of 200 mm (Nicolescu, 2005).

The assembly elements from Figure 2 were studied as kinematics in the working environment CATIA V5 R16 for verifying and illustrating the well functionality of the assembly of the two elements, but also from a verification point of view of the rotation angle (18[degrees]) of the cam (Preben & Jensen, 1987).

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

The functionality analysis of the effector was accomplished by a parallel and comparative analysis of two geometrically different models of the cam (model 1 with line straight profile and model 2 with curved profile).

3. FINITE ELEMENTS ANALYSIS

For the application with the finite elements method (FEM) analysis, the steps which were taken were the typically steps followed for an analysis of this type. The main steps were: Geometry (including Part analysis and characteristics); Connections (the contact zone between the two elements of the partial assembly push rod-cam); Discretization (including the Mesh with nodes and elements); Static structural analysis (sets, loads, results, stress, maximum deformations).

For presenting the Geometry of the FEM analysis of the assembly push rod-cam, Figure 4 illustrating the geometry of the two parts, which were modelled in the working environment CATIA V5 R16 and then imported as a STEP format in the working environment ANSYS. Figure 4 presents: a) model 1, the initial cam; b) model 2, the modified cam.

[FIGURE 3 OMITTED]

The push rod will be pushed with a force which will have to move the cam around X axis for obtaining a rotation angle of 18[degrees]. The analysis will illustrate the deformations which appear in the contact area between the two elements on a specific scale. The axis system is automatically chosen by ANSYS.

Between the two cam profiles there are differences: the cam profile from model 2 has been modified, the contact area push rod-cam has a curved profile; this modification is useful especially for the strains distributions which appear at the surface level (Dhombre & Khalil, 2007).

For the structural static analysis in the finite elements method, the partial assembly push rod-cam was linear discredited with tetrahedral elements; totally, were obtained for the cam model 1: 2608 Nodes, 510 Elements, and for the model 2: 2957 Nodes and 593 Elements.

On the meshed models, on the contact push rod-cam were applied load for each model of 200 Pa.

The results which were obtained with the FEM analysis in the ANSYS working environment are presented below in the two Tables, for each cam model with the initial line straight profile and the curved profile.

Figure 5 illustrates the analysis of the Equivalent von Misses Elastic Strain for both model 1 (a) and model 2 (b) of the cam and the maximum value positioning.

Besides the values obtained and mentioned in the two tables, there were also obtained the values for the total deformations for also both models of the cam.

Figure 6 points out the distribution of the total deformations, for cam model 1 (a) and cam model 2 (b); the total deformations are graphically represented by screen captures of the working environment and also by a diagram in which the values of the two cam models are compared with each other (Zaeh & Baudisch, 2003).

[FIGURE 4 OMITTED]

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4. CONCLUSIONS

By modelling the kinematic functionality in the CATIA working environment of the assembly, two parameters could have been modified: the rotation angle of the cam models and the linear displacement of the push rod, all these, corresponding to both the specific kinematics of the mechanism and the limits conditions for driving the effector.

After the analysis of the stress strain and total deformations areas, for each geometrical model of the cam, another important conclusion came out of the present study: the determination of the optimal profile of the cam from the point of view of the strains and deformations of the partial assembly push rod-cam.

We have planned to develop more researches for a larger range of prehensile systems types for different loads.

5. REFERENCES

Dhombre, E. & Khalil, W. (2007). Robot Manipulators: Modelling, Performance Analysis, and Control, Publisher: ISTE Publishing, ISBN: 190520910X

Neugebauer, R., Denkena, B. & Wegener, K. (2007). Mechatronic Systems for Machine Tools, CIRP-Annals--Manufacturing Technology, Vol. 56, Issue 2, p. 657-686, ISSN: 0007-8506, Imprint ELSEVIER

Nicolescu, A.F. (2005). Industrial Robots (in Romanian), EDP Publishing House

Nicolescu, A.F. (2009). Industrial Robots Implemented into Robotic Manufacturing Systems (work in progress in Romanian), EDP Publishing House

Preben, W. & Jensen, J. (1987). Cam design and manufacture, Publisher CRC Press, ISBN 0824775120, 9780824775124

Zaeh, M. F. & Baudisch, T. (2003). Simulation environment for designing the dynamic motion behaviour, Proceedings of the Institution of Mechanical Engineers, ISSN 0954-4054, Professional Engineering Publishing

Tab. 1. Results for model 1 of the cam

 Definition

Type Equivalent Maximum Middle
 (von-Misses) Principal Principal
 Elastic Strain Elastic Strain Elastic Strain

 Results

Min. 1.7681e-021 -2.305e-015 -9.7277e-011
 m/m m/m m/m
Max. 2.4375e-009 3.0899e-009 3.974e-010
 m/m m/m m/m

Tab. 2. Results for model 2 of the cam

 Definition

Type Equivalent Maximum Middle
 (von-Misses) Principal Principal
 Elastic Strain Elastic Strain Elastic Strain

 Results

Min. 4.0161e-022 -4.6574e-022 -1.0936e-009
 m/m m/m m/m
Max. 5.8189e-009 3.2323e-009 7.2944e-010
 m/m m/m m/m