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Title page for ETD etd-03312006-100035

Type of Document Dissertation
Author Shen, Xiangrong
Author's Email Address xiangrong.shen@vanderbilt.edu
URN etd-03312006-100035
Title Exploiting Natural Characteristics of Pneumatic Servo-Actuation Through Multi-Input Control
Degree PhD
Department Mechanical Engineering
Advisory Committee
Advisor Name Title
Michael Goldfarb Committee Chair
Eric J. Barth Committee Member
Kenneth D. Frampton Committee Member
Nilanjan Sarkar Committee Member
Robert E. Bodenheimer Committee Member
  • haptic interface
  • stiffness control
  • PWM control
  • pneumatic system
  • servo control
  • energy saving
  • Pneumatic control -- Energy consumption
  • Pulse-duration modulation
  • Actuators -- Design and construction
Date of Defense 2006-03-29
Availability unrestricted
This dissertation presents the research on four advanced topics concerning the pneumatic servo-actuation through multi-input control. The first topic is Nonlinear Model Based Pulse Width Modulated Control of Pneumatic Servo Systems. In this work, an averaging approach, which describes the equivalent continuous-time dynamics of a PWM controlled nonlinear system, is developed and applied to a pneumatic actuator controlled by a pair of three-way solenoid actuated valves. The pneumatic actuation system is transformed into its averaged equivalent control canonical form and a sliding mode controller is developed based on the resulting model. Experimental tracking performance demonstrated the effectiveness of the proposed approach. The second topic is Simultaneous Force and Stiffness Control of a Pneumatic Actuator. This work involves the design of a robotic actuator with physically variable stiffness. The proposed approach leverages the dynamic characteristics inherent in a pneumatic actuator, which behaves in essence as a series elastic actuator. Based on this notion, a control approach is developed for the simultaneous control of stiffness and output force, as well as a control law for the specific case of force control of maximum or minimum stiffness. The third topic is On the Enhanced Passivity of Pneumatically-Actuated Impedance-Type Haptic Interfaces. This work proposed an approach to achieving a stable, high-stiffness surface in a haptic interface by leveraging the open-loop properties of pneumatic actuators. By utilizing the open-loop component of actuator stiffness as a primary component of stiffness simulation in a haptic interface, the system requires a comparatively small component of simulated stiffness from closed-loop control of the actuator. The enhancement of the stability range is demonstrated by both a stability analysis and experimental results. The last topic is Energy Saving in Pneumatic Servo Control Utilizing Inter-Chamber Cross-Flow. The energy saving is achieved by supplementing the standard configuration of a four-way valve controlled pneumatic system with an additional two-way valve that enables direct flow between the cylinder chambers. The inter-chamber crossflow enables the recirculation of the pressured air, thus saves the energy in the compressed air that would otherwise be exhausted to the atmosphere. A control approach is presented to utilize the crossflow, to the extent possible, to supplement the mass flow required by a sliding mode controller with the recirculated mass flow provided by the crossflow valve. Experimental results indicate an energy saving of 25% to 52%, with essentially no sacrifice in the tracking performance.
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