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20 April, 2018

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X-Y gantry has an axis that rotates through 20 degrees

21 November, 2016

The US motion engineer Intellidrives has developed a large-area X-Y gantry in which one of the axes can be rotated through more than 20 degrees. This novel approach to kinematics allows large relative motions of independent (X1 and X2) parallel axes to control orthogonality in the X-Y plane, or to introduce large theta rotation of the Y-axis about the X1 and X2 axes, as well as rotating the Y-axis around a virtual programmable point.

Intellidrives says that the gantry design covers a larger working area than delta robots, which are also more expensive and bulky.

In traditional X-Y gantry designs, the upper gantry member (Y-axis) is carried by two identical lower axes (X1 and X2) with motor/screw/bearing systems separated by distance orthogonal to the direction of the axes.

Imprecision in the components – such as linear guide deflections, ballscrew lead errors, and misaligned axes – affects the variation of the position errors in the X1 and X2 axes, and the orthogonality of the X-Y gantries. As a Y-axis carrying a load traverses the X-Y plane, it also introduces X-axis position errors that depend on the Y-axis position.

The current way of tackling this challenge is either to implement 2D position error-mapping, or to suspend the Y-axis on flexible members and to control the X1 and X2 axes independently to ensure orthogonality. But this reduces system bandwidth and provides a small range of angle adjustment – usually not more than 1 degree.

There are also many applications where a large theta angle is an intentional feature of the design to align the work tool with non-orthogonally located objects, or to align patterns.

Intellidrives’ X-Y gantry allows one of the axes to rotate through an angle of 20 degrees or more.

Intellidrives’ new X-Y gantry, where the theta angle can exceed 20 degrees, contains two pivot points on X1 and X2 axes that allow the Y cross-axis to rotate around each X-axis and be displaced linearly about each of them.

The current system uses motorised ballscrew actuators with brushless servomotors/encoders, but it could also be implemented using direct-drive linear servomotors. Optional Z-axes could also be added.

A dual-axis controller controls the X1 and X2 positions and theta (X1-X2) independently. This allows the axes to be displaced by any programmable distance and, in turn, allows Y-axis rotation around any programmable pivot point.

The system has been designed for an X-Y travel of 800 x 800mm, with 20 degrees of Y-axis rotation. It can operate at X-Y speeds of up to 300mm/s and resolutions of 2.5µm. The theta angle control achieves a resolution of 1 arc-sec with a repeatability of 3 arc-sec.  Intellidrives says that the design could be adapted to larger X-Y travels and theta adjustments.

The gantry has already been used successfully to manufacture semiconductor wafers and flat-panel displays.




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