Machines today are designed with many novel mechanical configurations which allow for greater simplicity of design, lower cost, and higher precision. Unfortunately, simplicity in the mechanics results in a system where moving in a straight line involves profiling multiple motors in complex trigonometric trajectories. Using a motion controller to perform these coordinate transformations allows an operator to command the machine in a familiar coordinate system. Each of the motors perform the required profile in order to smoothly move the load along the desired path.
An example of an elegant but non-Cartesian mechanics is the ALIO Industries Hybrid Hexapod® stage. This six degree of freedom stage consists of a tripod mounted on an X-Y stage. The final degree of freedom is a rotational axis on the top of the tripod.
This practical but highly coupled mechanical arrangement provides high accuracy in all six degrees of freedom.
The six degrees of motion which may be commanded are the 3 Cartesian coordinates (X, Y, and Z) as well as 3 forms of rotation (yaw, pitch and roll). Commanding motion in one direction in physical space may involve anywhere from one to all six motors moving in coordination. For instance to move straight up in the Z axis, it is necessary to extend all 3 legs of the tripod simultaneously. The user could simply compute the final point for each motor in a host PC and move them all independently, but to move along a desired path in any combination of axes requires a transform solution for every point on the trajectory. This is best performed in the motion controller.
A further advantage to performing the transform in the controller is that complex motions may be performed. For instance there may be a requirement for rotation about a tool's center point (TCP) offset several inches from the stage. With the proper equations the controller will perform this motion by commanding all of the motors to create smooth accurate motion of the load about that point. When done properly, the operator is unaware that this isn't the stage's natural coordinate system.
Below is a video showing an example of the Hybrid Hexapod® controlled by a DMC-4060 performing two different moves. The first is a yaw motion about a tool center point. The second is motion commanded on the pitch and roll axes around the same tool center point. A simple GUI is used to input the user defined point.
Ease-of-use and cost effective solutions are requirements in most of today's machine designs. These two constraints are often at odds in innovative mechanical designs. With a Galil motion controller to perform the coordinate transformations, cost effective mechanics can provide smooth and accurate motion. The coordinate transformations can be used to define a coordinate system independent of the mechanical system. This gives the user flexibly to use a coordinate system that is most convenient for their application.