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ETEL: Rotary Axes (RTTB Series) ETEL: Rotary Axes (RTTB Series)

ETEL: Rotary Axes (RTTB Series)

Motion Systems

As a worldwide leader in Direct Drive Technology, ETEL has built its outstanding reputation over the past 40 years by providing state‐of‐the‐art, highly reliable and unique products dedicated to Motion Control. Benefiting from multi‐disciplinary competences in magnetic designs, bearing technology, metrology concepts, motion control architecture, simulation tools and materials, ETEL is a supplier of choice for advanced mechatronics solutions.


ETEL offers a wide range of motion systems, from stand alone products to highly integrated platforms. It addresses the most stringent requirements mainly in semiconductor and electronics applications, allowing the machine builder to focus on his core competence.


Design


XY Table

This construction provides the simplest form of 2 linear degrees of freedom of a positioning system where the base of the top axis is screwed to the carriage of the lower axis.

  • Ironcore linear motors with reduced cogging

  • High precision linear encoder

  • High precision recirculating caged ball bearings, for stiffness and smooth running

  • External cable management system


Gantry System

This configuration has the best accessibility to the space around it per footprint of the machine. It is commonly used as single cell, or in process application where several machines are operating over a conveyor.

Gantry configuration, driven by linear motors and designed for high natural frequency, can provide an excellent solution that combines high precision, high speed and low settling time.


Rotary Table

The rotary table's performance, which significantly exceed levels achieved with a conventional solution, is determined by the best integration of these elements:

  • High performance torque motor

  • Precision bearings

  • High precision rotary encoder

  • High rigidity mechanical structure


Definitions


Abbé Error

The Abbé error is a linear positioning error caused by a combination of an angular error in the bearing ways (way of motion), and an offset distance between the measuring device (lead screw, encoder, etc) and the actual point of interest.

?=h x tan?

with h being the distance between the encoder and the tool point. To minimize the Abbé error, the distance h must be as short as possible.


Accuracy

The accuracy is the difference between the actual position of a mechanical system and the expected position. It is typically specified in micron or arcsec per given travel for a deviation of ±3sigma. For example, an accuracy of ±3µm20arcsec), at ±3sigma, per 300mm (300°) travel means that if the axis moves to a position 300 mm (300°) away from the current position, the final position will end between 299.997 (300.0056 deg) and 300.003 (299.9944 deg), 99.7% of the time. The accuracy is influenced by the feedback system (encoder, laser interferometer...), the drive mechanism and the type of bearing.


Axial R
unout

The axial runout is the positioning error of the top of a rotary table in the vertical direction when the table is rotating in the horizontal plane.


Backlash

The backlash is an error in positioning caused by the reversal of travel direction. It is caused by a clearance between the elements of the mechanical system. The backlash also affects the bidirectional repeatability. The backlash can be compensated by the position controller.


Coefficient of F
riction

The coefficient of friction is the ratio of the force required to move load to the magnitude of that load. There are two coefficients: the static and the dynamic one (static coefficient > dynamic coefficient).


Duty Cycle

For a repetitive cycle, the duty cycle is the ratio of ’on’ time to total cycle time. Duty Cycle = (on time/(on time + off time)) x 100%.


Flatness

The flatness is a vertical deviation from the plane of travel.


Horizontal S
traightness

The horizontal straightness is a horizontal deviation from the straight line of travel. An horizontal straightness deviation in the travel of the X-axis will cause a positioning error in the Y direction.


Hysteresis Error

The hysteresis error is a deviation between the actual and the commanded position caused by elastic forces accumulated in the motion system. It affects the accuracy and the bidirectional repeatability.


Orthogonality

The orthogonality is the degree of perpendicularity between the line of travel of the two stacked axes. If the two travel lines are not orthogonal, the Y-axis travel creates a positioning error in the X direction (for a X-Y table).


Pitch

The pitch is a rotation (angular deviation from the ideal straight line of travel) around an axis in the horizontal plane (for the example mentioned below) perpendicular to the direction of travel. For the X-axis travel, a pitch will cause an Abbé error in the X and Z directions.


Radial R
unout

The radial runout is the positioning error of a rotary table’s centering diameter in the horizontal direction when the table is rotating in the horizontal plane.


Repeatability

The repeatability is the ability of a motion system to reliably achieve a commanded position over many attempts under identical conditions. The unidirectional repeatability is the ability to repeat a movement in one direction only (and ignores the effects of backlash or hysteresis within the system). The bidirectional repeatability is the ability to repeat a movement from both directions. By default, the measurement of the repeatability is made with unloaded system.


Resolution

The resolution is the smallest possible movement that can be achieved by a system. It can be defined at the electronics, encoder and mechanics level.


Roll

The roll is a rotation (angular deviation from the ideal straight line of travel) around an axis in the horizontal plane (for the example mentioned below) parallel to the direction of travel. For the X-axis travel, a roll will cause an Abbé error in the Y and Z directions.


Sigma

Sigma (s) is the standard deviation. It indicates how far a given process deviates from the nominal value, the lower the better. For a normally distributed movement, which is often assumed for position values, a result of 3s=0.1micron (=2arcsec) guarantees 99.7% of the measurement to be between ±0.1micron (2s=0.1micron leads to 95.4% between ±0.1micron, s=0.1micron leads to 68.3% between ±0.1micron) or ±2arcsec (2s=2arcsec leads to 95.4% between ±2arcsec, s=2arcsec leads to 68.3% between ±2arcsec).


Thermal E
xpansion

The thermal expansion is a change of the size and shape of a system when the temperature is modified. The amount of change is dependent on the size of the component, the degree of temperature change and the characteristics of the material.


Vertical S
traightness

The vertical straightness is a vertical deviation from the straight line of travel. A vertical straightness deviation in the travel of the X-axis will cause a positioning error in the Z direction.


Wobble

The wobble is the angular error between the perpendicular to the interface plate and the actual axis of rotation, when the beta (b) and gamma (g) angles are corrected.

(a): angle with the fastening surfaces
(b): angle between the actual axis of rotation and the base of the rotary table
(g): angle between the perpendicular to the interface plate and the actual axis of rotation


Yaw

The yaw is a rotation (angular deviation from the ideal straight line of travel) around an axis in the vertical plane (for the example mentioned below) perpendicular to the direction of travel. For the X-axis travel, the yaw will cause an Abbé error in the X and Y directions.

ASME-RTTB01800202PAS0367-T Standalone Axis

ETEL has a large portfolio of off-the-shelf rotary axes, available in different sizes, accuracy grades, and with different options to provide you an optimized solution to cope with the needs of applications involving:

  • Speed stability

  • Highly dynamic indexing

  • Nanometer positioning stability

  • Small runouts

  • Dynamics

  • Cleanliness


The RTTB axis is the first direct driven rotary stage on the market capable of nanometer position stability at a working diameter of 450 mm. This is made possible thanks to the unprecedented high resolution encoder coupled to an outstanding mechanical bearing.

This table is especially well suited for application requiring:

  • Smoothness of motion, high speed stability, low tracking error

  • Super high repeatability

  • Very good positioning accuracy without calibration

  • Outstanding position stability

  • Outstanding radial and axial runout

  • ISO1 cleanroom compatible


Main F
eatures:

  • Bidirectional repeatability ±0.3 arcsec

  • Position accuracy ±3 arcsec (w/o calibration)

  • Speed up to 60 rpm

  • Load capacity 30 kg