Automation And Robotics
Application Challenge: Maximize accuracy, smoothness, and speed
Microscope x‐y stages need fast, smooth, and accurate motion for highest performance. In addition, we want to use the most cost effective hardware that can get the job done. What control techniques are available to achieve these goals?
|Number of Axis:||2 independent servo motors|
|Motion mode:||Multi‐axis point‐to point|
|Control architecture:||Chip or card‐based|
Motion Control Solution
The diagram on page two shows an all‐in‐one motion card design utilizing a Magellan® motion control IC. This card connects to two motors and four encoders: one rotary encoder on each motor, and one linear encoder on each axis.
Motion Control Components
|Motors||Brushless DC motor w/ encoder
|Rotary encoder resolution needs to be high enough to allow for accurate velocity control. This depends on the ratio between rotary and linear position. 1,024 counts/rotation or less is typical.
|Controller:||Custom designed card using
Magellan® MC58420 IC and two ICbased
Brushless DC motor amplifiers
|X‐Y Stage||Lead screw‐based linear stage with linear encoders on each axis.||Linear encoders translate directly to the final positioning accuracy and should be at least twice the desired resolution required for the application.
Dual Encoder Configuration
To maximize positioning accuracy, a dual encoder configuration (dualloop control) is used. This owerful technique allows one encoder (on the motor) to be used to stabilize the motion, while the second (on the stage) is used for positioning accuracy, with all of the control details handled by the Magellan chip. Dual‐loop corrects automatically for mechanical errors from backlash, lead screw or table assembly non‐linearities.
SCurve Motion Profiling for reduced vibration
Adding S‐curve motion profiles can substantially reduce vibration over trapezoidal profiles. Often, only a small amount of "S" (transition between acceleration and no acceleration) can substantially reduce induced vibration. The form of the s‐curve will depend on the desired performance required. For X‐Y stages that involve liquid transfers or fragile material that should not be jostled, it would be appropriate to choose an s‐curve profile that spreads the acceleration transitions out as far as possible, thereby maximizing smoothness of motion. Other loads can use a shorter "S" period. Magellan can also provide trapezoidal, velocity contouring, and electronic gearing motion profiles as alternatives to s‐curve profiles.
The figure above illustrates the motion control card and connections needed to implement a precision X‐Y stage controller. This system could also have been constructed using other PMD products such as a Prodigy® motion card. Contact your PMD representative for more information.
The Magellan® Family of Motion Control ICs provides high performance chipbased motion control for multiple motor types. Magellan motion control ICs are available in 1, 2, 3, and 4‐axis versions. They are designed for demanding and precise applications such as this microscope X‐Y stage application and other scientific instrumentation challenges. X‐Y stage motion control card diagram
Contact our customer support team at +1 978.266.1210 for more information including details on Developer’s Kits and application support. We would like to assist you in improving your motion system.