Terminology 1: Linear Positioning Stages

If you are new to working with precision mechanical positioning systems the terminology used in specification sheets can be confusing.  The terms below are the most common 

• Resolution - should be defined as either theoretical or actual. 
• The theoretical, or design resolution is the smallest incremental step a positioner can make without taking into account mechanical stiction.  In a closed loop positioner it will be the smallest incremental step that can be measured by the encoder.
• The actual resolution, or minimum incremental step, is the smallest step the positioner can reliably make taking into account all mechanical effects.
• Repeatability - un-idirectional or bi-directional.
• Uni-directional repeatability is how precisely a positioner returns to a given location when always approaching it from the same direction.
• Bi-directional repeatability is how precisely a positioner returns to a given location when approaching it from any direction.
• Backlash - the mechanical play due to slack in a positioner when the motor changes direction. Sometimes this is used to define the bi-directional repeatability.
• Hysteresis - like backlash this error occurs when the positioner changes direction.  Typically hysteresis is much smaller than backlash because it is due to the relaxation of elastic forces that build up in the mechanics.
• Accuracy or Linearity - defines how precisely the positioner follows the programmed trajectory.  Many factors will contribute to accuracy including hysteresis and encoder non linearity.  Positioners with the highest accuracy will have a linear encoder directly measuring the location of the moving platform.
• Runout - how the positioner (moving in X) deviates from a straight path, includes:
• Flatness - deviation in the Z plane
• Straightness - deviation in the Y plane
• Pitch - rotation about Y
• Yaw - rotation about Z
• Roll - rotation about X
• Orthogonality - angular deviation caused by mounting error between two or more axes.
• MTBF - mean time between failure, highly application dependent.

More terminology to follow in weeks to come on rotary positioners and piezo positioners.

PI - An Introduction

If you don't know about PI this is a good place to start.  I have included some brief information below on who we are and what we do.
With headquarters and four factories in Germany the company has a global presence with more than 750 employees worldwide.  There are subsidiary offices offering sales, service and in some cases local R&D and manufacturing in all major markets around the world.
The company develops and manufactures precision positioning systems and a range of technologies based on piezo ceramics.  We supply into a diverse range of markets including microscopy, medical device, semiconductor, metrology, photonics, aerospace, defence and university R&D.  Our knowledge and experience extends from supplying complex multiaxis vacuum compatible positioning systems into synchrotrons to providing high quality, high volume piezo ceramic components used in medical products.

 Miniature Hexapod

If you want to know more about our any of our areas of expertise please follow the links below.

• Hexapods
• Customised Multixis Positioning Systems
• Motorised Lineat Stages
• Motorised Rotary Stages
• Nanopositioning Systems
• Piezo Actuators
• Piezo Motors
• Piezo Ceramics

Our job at PI UK is to help you identify the most appropriate technology to solve your positioning or sensing application.  We do this best by getting involved early on in a project.  All my colleagues are technically trained and ready to consult with you.  If you are based in the UK or Ireland and want to get in contact please send us an email or call us on 01234 756360.  Alternatively please visit our global contact page.

PI - An Introduction