How to Formulate a Differential Equation for Deformable Object Manipulation?

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Discussion Overview

The discussion revolves around formulating a differential equation for the deformation of objects manipulated by a robot with a two-finger gripper. Participants explore the theoretical and mathematical aspects of modeling object deformation, particularly in the context of robotics and material behavior.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant seeks references for formulating a differential equation related to the deformation of objects manipulated by a robot gripper, considering standard first or second order processes.
  • Another participant notes that the bending of beams is described by a fourth-order equation, referencing Euler-Bernoulli beam theory, but expresses uncertainty regarding solid objects that deform in multiple directions.
  • A different participant suggests writing equations of equilibrium and applying stress-strain relations, mentioning that this could lead to coupled partial differential equations that typically lack closed-form solutions.
  • One participant specifies an interest in one-dimensional deformation along the gripper's displacement and proposes modeling the reactive force from the object as a spring, potentially incorporating dynamics for non-instantaneous shape retention after release.
  • A participant provides a mathematical expression for the force from the object and seeks guidance on the acceleration equation, expressing skepticism about the applicability of finite element methods for their simpler needs.

Areas of Agreement / Disagreement

Participants express various approaches and models for the problem, with no consensus reached on a single method or solution. Different perspectives on the complexity of the equations and the dimensionality of the deformation are evident.

Contextual Notes

Participants mention the potential complexity of the equations involved, including the possibility of needing to solve multiple coupled partial differential equations, and the limitations of finite element methods for simpler scenarios.

Liferider
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I'm working on manipulation and moving deformable objects by use of a robot with a 2-finger gripper. I would like to form a differential equation for the object deformation and I'm wondering where I could find some papers that has been dealing with this issue. I have thought about just assuming a standard first or second order process for the deformation, but it would be nice to have some references for my choices. Any comments are welcome.
 
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IN principle, you just write down the equations of equilibrium for the object, plus the stress-strain relations for the material, solve the resulting partial differential equations for the boundary conditions of the object, and then integrate the strain field to get the displacements.

There are lots of software packages that can do that numerically - google for "finite element analysis."

On the other hand, if you really "want to form a differential equation", you will end up with maybe 12 or more coupled partial differential equations, which usually don't have a closed-form solution.

I think what you really need to first is get clear in your mind what you want to calculate and how you plan to use the results, and then start investigating how to calculate it.
 
I am basically only concerned with the deformation in one dimension, the one along the gripper displacement. I also want to express a reactive force from the object, acting on the gripper fingers. Maybe I can model the reactive force as a spring (linear or not). And I would also like to include some dynamics such that the object does not retain its shape instantaneously (after a finger release).
 
Last edited:
Here are some math:
Force from object
\begin{equation}
F_{ob} = k_s (x_{ob,0} - x_{ob})
\end{equation}
\begin{equation}
\ddot{x}_{ob} = ?
\end{equation}
where $x_{ob,0}$: Equilibrium width, $x_{ob}$: Actual width. I just need to be pointed in the right direction. Regarding FEM methods, I just think it would not serve my simple purpose.
 
Last edited:

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