Engineering

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Introduction:

Finite Element Analysis of a Pneumatically Actuated PDMS FingerThe pneumatic fingers are designed as a part of a surgical parallel robot system which is remotely controlled by a surgeon through the internet.These fingers are made of a PDMS-based (polydimethylsiloxane) elastomer material which belongs to a group of polymeric organosilicon compounds that are commonly referred to as silicones. PDMS is the most widely used silicon-based organic polymer, and is particularly known for its unusual rheological (or deformation and flow) properties. It is optically clear, and, in general, inert, non-toxic, and non-flammable.PDMS is viscoelastic in nature and acts like a viscous liquid, similar to honey. However, at short flow times (or low temperatures), it acts like an elastic solid, similar to rubber. The finger is fabricated through PDMS molding process and the PDMS-to-PDMS bonding process. The finger contained chambers in it which are located closer to the upper face than the bottom face so that when pneumatic pressure applies, the finger bends downward.Here in the finite element analysis we used half-section of the finger so that the chambers inside the finger can be seen easily.

 

Objective:

The goal is to assess the efficiency of the design, defined as the magnitude of the actuation (the vertical deflection) under a working air pressure up to 200 kPa and to plot the pressure versus deflection chart.

Geometry:

For analysis half-section of the geometry is taken due to symmetry. The 2-Dimensional geometry and 3-D model of the PDMS finger is shown below.

 

2D geometry

All dimensions are in mm.

 

Model

The Model was Designed in ANSYS - (Design Modeler)

 

Material Properties:

The material properties of the PDMS elastomer are as follows

 

 

material properties 

 

Methedology:

 

methodology

 

Case I:-  Linear Static Solution:-

In this case the solution was obtained by linear static method with the following Mesh Parameters.

 

mesh pic 1

mesh pic 2

 

Case II:- Non-Linear Solution:-

In this case the solution was obtained by non-linearly by keeping Auto time stepping and Large Deflection option “ON”. The  mesh parameters were same as in the “Case I”.

 

pic 1

 

pic 2pic 3

 

Case III:- Non-Linear Solution:-

In this case the solution was obtained by non-linearly by using “Multizone meshing” method. Auto time stepping and Large Deflection conditions were same as in the “Case II”.

 

pic 4

 

Application of Load and Boundary Conditions:-

As per the problem statement a pneumatic pressure of 0.2 MPa is applied to all the faces (Total 70 faces) of 14 chambers. One of the faces was constrained by the “fixed support” and the another one by “Frictionless Support”. By using theseboundary conditions static structural analysis is performed.

 

Pressure:-

 

pressure

 

Fixed Support:-

 

fixed

 

Frictionless Support:-

 

frictionless

 

Results & Discussion:-

 

Case I:-

The Linear Static Analysis was done by applying the above mentioned Boundary conditions. After analysis it is found that the maximum  directional displacement along Y-axis is 1.1008mm. The maximum Von-Mises stress on the model is 1.026 MPa.The directional deformation and Equivalent-Stress plot is given below.

 

displacement of finger

 Displacement Plot

 

 

eq1

 Equivalent Stress Plot 

 

Case II:-

The Non-Linear Analysis was done by applying the above mentioned  Boundary conditions. After analysis it is found that the maximum  directional displacement along Y-axis is 1.1299mm. The maximum Von-Mises stress on the model is 1.3514 MPa .The directional deformation, Equivalent-Stress and Pressure versus Deflection plot is given below.

 

DD2

 Displacement Plot 

 

eq2

 Equivalent Stress Plot 

 

g1

 Pressure VS Deflection 

 

Case III:-

The Non-Linear Analysis was done by applying the above mentioned  Boundary conditions. After analysis it is found that the maximum  directional displacement along Y-axis is 1.2213mm. The maximum Von-Mises stress on the model is 1.3466 MPa .The directional deformation, Equivalent-Stress and Pressure versus Deflection plot is given below.

 

dd3

 Displacement Plot 

 

eq3

 Equivalent Stress Plot 

 

g2

Pressure VS Deflection 

 

Reference:- Problem by Huei-Huang Lee.