Snow Edward R.

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Snow
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Edward R.
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1993 - 1999 2
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  • Thesis
    Advances in grasping and vehicle contact identification : analysis, design and testing of robust methods for underwater robot manipulation
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1999-05) Snow, Edward R.
    This thesis focuses on improving the productivity of autonomous and telemanipulation systems consisting of a manipulator arm mounted to a free flying underwater vehicle. Part I minimizes system sensitivity to misalignment by developing a gripper and a suite of handles that passively self align when grasped. After presenting a gripper guaranteed to passively align cylinders we present several other self aligning handles. The mix of handle alignment and load resisting properties enables handles to be matched to the needs of each task. Part I concludes with a discussion of successful field use of the system on the Jason Remotely Operated Undersea Vehicle operated by the Woods Hole Oceanographic Institution. To enable the exploitation of contact with the environment to help stabilize the vehicle, Part II develops a technique which identifies the contact state of a planar vehicle interacting with a fixed environment. Knowing the vehicle geometry and velocity we identify kinematically feasible contact points, from which we construct the set of feasible contact models. The measured vehicle data violates each model’s constraints; we use the associated violation power and work to select the best overall model. Part II concludes with experimental confirmation of the contact identification techniques efficacy.
  • Thesis
    The load/deflection behavior of pretensioned cable/pulley transmission mechanisms
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1993-12) Snow, Edward R.
    Mechanical transmission mechanisms enable a designer to match the abilities (e .g. velocity, torque capacity) of an actuator to the needs of an application. Unfortunately the mechanical limitations of the transmission (e.g. stiffness, backlash, friction, etc.) often become the source of new problems. Therefore identifying the best transmission option for a particular application requires the designer to be familiar with the inherent characteristics of each type of transmission mechanism. In this thesis we model load/deflection behavior of one particular transmission option; closed circuit cable/pulley transmissions. Cable drives are well suited to force and position control applications because of their unique combination of zero backlash motion, high stiffness and low friction. We begin the modelling process by determining the equilibrium elongation of a cable wrapped around a nonrotating pulley during loading and unloading. These results enable us to model the load/deflection behavior of the open circuit cable drive. Using the open circuit results we model the more useful closed circuit cable drive. We present experimental results which confirm the validity of both cable drive models and then extend these models to multistage drives. We end by discussing the use of these models in the design of force and position control mechanisms and comment on the limitations of these models.