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DIGITAL CLAY
Motivation
  Shape is an important and tangible element in our visual and haptic communication
  Importance for human to understand and interpret complex information
  Areas of engineering, art, sciences, medicine, entertainment etc.
  2-D to 3-D technology
  What alternative input to current human-machine interface?
Digital Clay is an array of fluidic driven actuators for display of shape and haptic feedback. The
importance of shape in almost all aspect of life serves as the motivation for this next generation
human-machine interface. The user can command the device to display any surface in 2.5-D and
shape/ edit the surface.
The greatest challenge is to be able to simulate material behavior and properties with the Digital
Clay. This system was realized by Dr. Haihong Zhu, CTO Sentrinsic LLC,
(http://www.sentrinsic.com/) while working as a PhD student under Dr. Wayne Book in the
Intelligent Machine Dynamics Laboratory (IMDL) of Georgia Institute of Technology. The
current testbed is a 5x5 array of fluidic actuated pins. The sub-systems on this test-bed consists
of:
  Micro-miniature On-Off valves
  Actuator embedded displacement sensors
  Hydraulic Matrix drive system
  Hardware Implementation
  RT Linux host computer
GOAL: Improvement on the control algorithm; give more intelligence to the controller
1. Velocity command to simulate material properties
2. Force feedback for haptic sensation
Ideally, displacement control based on pressure feedback
  Display mode: Displacement controlled to display shape
  Shaping mode: User can add/subtract volume
  Haptic mode: User exerts force; estimate the force and adjust displacement (velocity mimicking material behavior)
A simple experiment of input (PWM Duty) and Actuator force relationship for a single pin on the Digital Clay system showed non-linear relationship. Traditionally, force control of hydraulic actuators is very difficult and open-loop control is not feasible to obtain satisfying results.























First, some preliminary experiments are performed to better understand the dynamics and behavior of Digital Clay. To ensure that the system remains compact and as simple as possible, the amount of sensors have to be limited and methods of estimating system states will be used for control purposes. A velocity estimation method is studied and implemented on the system. Both open-loop and closed-loop force control methods are considered. Output feedback and model-based state feedback of force control are found to be the more realistic solution for accurate force display. A detailed mathematical model is derived for a single-actuator case and expanded to include full 5x5 array of control. Sensor-based and state estimates based types of feedback control are developed and simulation and experimental results are compared. Simulation and experiments are performed for single actuator case and expanded to include 5x5 arrays. The best control scheme would be implemented digitally on the current prototype for achieving the goal of force estimation and material property simulation. The performance will be evaluated and future work is presented.