MOSAIC-PM is based on a workstation/VME bus/Real time UNIX/C-language architecture. It is being used on a regular basis for a wide variety of demonstrations in 'intelligent systems and advanced manufacturing.' These demonstrations have included a) feature based machining, b) rapid prototyping by machining, c) networked manufacturing and d) sensor based machining. The goals of the demonstrations in sensor based machining are to improve the precision of the components being machined: i.e. to improve the capability of a 'standard' machine tool structure and give it some of the characteristics of a 'precision' machine. One routine uses a Renishaw touch trigger probe to inspect partially machined components after 'roughing'; the data collected are then used to modify the tool paths during 'finishing' to provide more precision. A second routine relies on a dynamometer to maintain constant force during cutting. This demonstration aims to achieve maximum precision by cutting at a constant force to keep tool deflection at a known value. During the demonstration, the dynamometer results are used as the feedback signal in the reference control loop of machining.
Grippers for an automated assembly cell are being developed for handling individual sub-millimeter hard-disc drive components. Processing requirements dictate positive gripping with a strong actuator that meets clean room specifications. Proof-of-concept testing of shape memory alloy (SMA) as an actuator was performed. The response time of Ni-Ti 0.076 mm diameter shape memory wire was found to be 0.15 seconds under forced air convection conditions. Positioning accuracy was held to steady-state oscillations of 0.076 mm proving that SMA actuators meet performance requirements for a precision microactuator. SMA was then used for the actuation of several candidate gripper designs. One promising design consisted of a two-fingered gripper with integral spring sections at the arm base. SMA wire provided the closing actuation force and the spring sections returned the fingers to their rest position. Another design used an external spring to provide the gripping force, while the SMA wire provided the force required to open the gripper. The paper describes design methodologies and overall results. The addition of closed-loop control and improved heat dissipation mechanisms are needed before SMA materials can be used robustly as actuators for sub-mm robot grippers in high volume applications.
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