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Tracing a complex continuous curve requires high repeatability. To achieve this, the design and manufacturing requirements called for low tolerance and high quality joints and low tolerances. The linkage joints used the provided bearings, shafts, and retaining clips as well as washers to minimize axial friction. This joint design was tested on two previous prototypes and proved satisfactory.
Picture of joints?
To scale up the drawing window of the mechanism, the link lengths were also scaled up. To maintain sufficient stiffness and to improve the stability of the joints, the links were made out of water-jet cut aluminum. The water-jet process was ideal for making this mechanism which consists of arbitrary planar geometries. The cam and cam carrier plate were also ideally suited for water jet cutting. The edge of cam was sanded and polished to ensure smooth reading. All holes and were cut undersized and then drilled and reamed to size for a precise fit.
The cam axle/bearing assembly was designed to minimize friction and eliminate play. An aluminum stand off holds a second bearing away from from ground plate to help resolve moments, and the input shaft is threaded for a lock-nut which pre-loads the bearings and removes any play in the system.
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The ground plate was made of plasma cut steel sheet. Steel was chosen as the base plate material to save cost, maintain stiffness, and add stability to the ground. The CNC plasma cutter allowed us to maintain precise relative dimensions between the cam and linkage. Like the water jet parts, all holes and were cut undersized and then drilled and reamed to size.
Manufacturing summary
Used water jet to cut complex cam curvature and links
Used plasma cutter for ground plate
use of numerically controlled processes allowed precise hole location, but poor hole quality
addressed this by undersizing and drilling to size
Press fit shafts and bearings into links for robust and smooth joints
Coupled motor to cam plate with shaft and bevel gears
Found proper springs to provide enough tension to keep followers in contact with the cam throughout the range of motion