System Design Considerations

It is important for the designer to:

• Review and thoroughly understand the application and the desired motion requirements.
• Determine if the application requires accuracy, repeatability, or resolution
• Develop a conceptual configuration.
• Formulate an error budget.
• Select the best component technologies to achieve the goals.
• Thoroughly understand the physical environment (acoustic noise, ground vibrations, EMI fields, temperature and humidity variations).

Keep in mind that:

Accuracyof motion is dependent upon structural stability, the precision of the guide bearings, precision of the measuring feedback system, and how well the motive forces are controlled.

• Stage configuration: Stacked XY; Split-axis; Gantry; Single-plane coplanar XY
• Bearing selection: Linear crossed roller; Linear ball; Recirculating ball; & Air bearings
• Servo controller: A high performance controller is essential for a high-precision system.

Stiffness of the mechanical structures is extremely important, i.e., do the support members twist, bend, or deflect when loads are applied (either by a mass, a motive force, or an external impulse)?

• Structure: This is one of the most critical elements in assuring precision of a machine's design: mechanical tolerances; thermal stability; etc.
• Damping: High damping structural materials are very important for machines that require rapid moves with quick settling. Anocast polymer composite structures are ideal for high damping.

Vibrations can greatly affect system precision, by reducing its stability and its ability to quickly settle to stop.

• Typical sources of unwanted external vibrations could be:
  • Nearby machinery
  • Road traffic
  • Machine not located on the ground floor
• Mounting the machine on vibration isolation is vitally important for very high-precision systems