The Remote Elastic Lock
The Remote Elastic Lock (REL) is the subsystem responsible for locking and releasing a tool on the carriage. While the kinematic coupling features on both carriage and tool do te work of locating tools to a consistent position, the REL locks it into place.
System Behavior
Properly locking a tool into the coupling at all 6 points of contact requires a nesting force a force applied that pushes the tool balls and carriage pins together. This nesting force is applied with the twist lock, which rotates into the wedge plate. As the twist lock rotates, the helical feature in the wedge plate creates both an axial and radial force applied from the shaft to the tool. The radial force is due to friction and should be minimized while the axial force is responsible for holding the tool in place. This process, when cycled thousands of times, will eventually wear out the wedge plate from the repeated rubbing, which will need to be replaced.
Detecting Locked/Unlocked Tools
When a tool is picked up, the twist lock rotates into the carriage to a specified setpoint at which point the tool is considered locked. This setpoint is not position-based, however, but torque-based. That is, only when a particular torque value is applied to the twist lock is a tool considered fully engaged. There are key advantages to a torque based locking system. First, the system is less susceptible to wear-and-tear. As the machine cycles through thousands of lock/unlock movements, either the twist lock pin or the wedge plate can eventually wear out. With a torque-based locking setup, tools will continue to lock consistently throughout the life time of the parts, rather than gradually degrading in reliability. Second, this setup makes Jubilee more ready to accommodate slight changes in geometry on the wedge plate feature. Even if wedge plates differ slightly from manufacturing processes, they will likely still work. One extension of this concept is that wedge plates can, in principle, be 3D printed. However, this is not recommended as the "stair-step" feature of the printing process can cause the twist lock to snag and twist the tool, rather than apply a majority axial force that pulls it into the locking position.