Rotation Stage with Resonant Piezoelectric Motors

ELL18(/M) Key Specifications a
Travel (No Limit Switches) b		360° Continuous
Homing Repeatability		1.75 mrad (0.1°)
Bidirectional Repeatability		873 µrad (0.05°)
Velocity (Maximum)		430 °/s
Maximum Total Load		200 g (7.05 oz) c
DC Voltage Input		4.5 to 5.5 V
Weight of Stage and Brackets		90 g (3.17 oz)
Minimum Lifetime		100 km (600 600 Revolutions)
Stage Dimensions (Without Brackets)		81.0 mm x 60.0 mm x 20.3 mm (3.19" x 2.36" x 0.80")

• See the Specs tab for complete specifications.
• Not Intended for Continuous Operation
• Maximum Load Must Be Centered on Stage

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The components of the ELL18K Rotation Stage bundle are shown connected and with key features labeled.

Thorlabs' Elliptec Technology for OEM

Features

• Ideal for OEMs and Applications Requiring Rapid and Precise Positioning
• Micro-B USB and Picoflex ^®1  Connectors for Control Signals
• Multi-Drop Serial Communication Protocol Supported
• Ø50.0 mm (Ø1.97") Rotation Stage
• Absolute Home Position Found with Infrared and Magnetic Sensor Technologies
• Magnetic Encoder Used to Position Stage
• Optional Accessories Offered Below
  • ELLA2 Filter Wheel Adapter with 12 SM05-Threaded (0.535"-40) Holes
  • ELLA3 Post Mount Adapter for Mounting the Rotation Stage Upright
  • Bus Distributor to Facilitate Control of up to Four Elliptec ^® Devices
  • ELLC2 Accessory Upgrade Pack

Driven by Thorlabs' Elliptec piezoelectric resonant motor technology, this rotation stage is designed to be a compact solution for applications requiring rotational control. The rotation stage is offered as a standalone unit (Item #'s ELL18 and ELL18/M), or as part of a bundle (Item #'s ELL18K and ELL18K/M), which also contains an interface board for manual control of the stage, mounting brackets, power supply, and cables for connecting the stage and interface board to each other and to a PC. Thorlabs also offers the ELLC2 Accessory Pack which can be used to upgrade standalone units to kits. Please note that the ELLC2 Accessory Pack does not include the brackets used in the ELL18K(/M) bundle.

Each stage has 37 8-32 (M4) tapped holes on 0.25" (6.4 mm) centers providing flexible mounting options. The rotation stage is lightweight and compact, and the closed-loop operation provides rotation to specified orientations with a repeatability of 873 µrad. The assembled components of the ELL18K(/M) are shown in the image to the far right, with key features labeled. Please see The Elliptec ^® Motor tab for more information.

The rotation stage can be mounted horizontally using the mounting brackets included in the ELL18K(/M) bundle or upright using the ELLA3 Post Mount Adapter (sold separately). The ELLA2 Filter Wheel Adapter, sold separately and shown in the image to the bottom right, can be mounted on the ELL18(/M) rotation stage and has 12 SM05-threaded holes for holding filters. For applications requiring switching between Ø1" filters, or with vertical space constraints, Thorlabs offers a variety of multi-position sliders  driven by Elliptec motors.

The motor is highly dynamic and has no gearing. The tips of both motor housings are in firm contact with the plastic track at the base of stage, as can be seen in the image at the right. The motors are installed with opposite orientations, and translation in both directions occurs when one motor pushes the track forward while the other pulls it backward. The rotation stage is not designed for continuous operation. We recommend operation with duty cycles of 40% or less. When power is not applied to the motors, the stage is held in place by an approximately 0.025 N·m combined torque exerted by the stationary arms of the motors.

The open frame format, versatility, and simplicity of this rotation stage makes it attractive for OEM applications, as it can be customized according to customer requirements and produced in high-volume quantities. Please contact us to discuss your specific requirements so that we may tailor a solution to meet the needs of your application.

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Assembled View

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Exploded View

The ELL18(/M) rotation stage is attached to the ELLA3 post mount adapter with four M4 screws. The ELLA2 Filter Wheel is then attached to the ELL18(/M) stage by aligning the silver pin (not visible) to an appropriate hole in the rotation stage, snapping the pieces together, and securing with an included 8-23 (M4) screw.

Control
There are multiple options for powering, driving, and controlling this rotation stage, which are detailed in the Positioning the Rotation Stage section of the Operation tab. The stage possesses a 3.3 V serial bus and is designed to be operated with or without the interface board; the Pin Diagram tab provides pin assignments. Thorlabs offers software for our Elliptec products capable of providing full and independent control of the stage. When the interface board is used as an accessory to change the position of the stage, its status in the software is automatically updated.

Multiple Elliptec devices can be controlled using the ELLB Bus Distributor or by splicing multiple connectors onto one ribbon cable. A single bus distributor can connect up to four Elliptec devices; up to 16 devices can be connected if the buses are daisy chained. This bus can be controlled one of three ways: through an interface board (included with the bundles below) to connect to a PC running the Elliptec software, by connecting to an Arduino ^®2  or Raspberry Pi ^®3  board, or by wiring the connector pins to a user-supplied control board. Alternatively, up to 16 devices can be spliced onto a single ribbon cord. The devices can then be simultaneously controlled by the interface board or selectively controlled by the Elliptec software. See the manual  for instruction on how to splice multiple devices onto a ribbon cord and the Pin Diagrams tab for pin assignments when making custom connections.

1. Picoflex is a registered trademark of Molex Incorporated.
2. Arduino is a registered trademark of Arduino Sa Société Anonym (SA).
3. Raspberry Pi is a registered trademark of the Raspberry Pi Foundation.

Elliptec Resonant Motor Products
Multi-Position Sliders	28 mm Linear Stage	60 mm Linear Stage	Rotation Stage	Rotation Mount	Motorized Iris

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Components of the ELL18K(/M) Bundle
(One Region-Specific Power Adapter Included with the Power Supply)

As shown in the image above, two mounting brackets are included with the bundle. The brackets fastens to the underside of the rotation stage's PCB with the four included screws. Each bracket features a slot for 1/4"-20 (M6) cap screws to secure the stage board to optical tables and breadboards. The bracket adds 0.05" (1.2 mm) of thickness to the profile of the stage.

The drawing below shows the dimensions and mounting features of the stage itself. The spacing and threading of the 37 mounting holes in the stage differs between the imperial (ELL18) and metric (ELL18/M) versions of the stage. All other dimensions, including the 1.97" (50.0 mm) diameter of the stage are the same for both.

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Mechanical Drawing of the Rotation Stage

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Mechanical Drawing of the Interface Board

Operation Notes

This tab contains information on handling, mounting, and operating the ELL18K(/M) Rotation Stage Bundle.

• Handling
• Mounting and Loading the Rotation Stage
• Supplying Power
• Operation of the Motors
• Homing the Rotation Stage
• Positioning the Rotation Stage
• Resonance Frequencies

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The Rotation Stage

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Features of the Rotation Stage

Handling

The rotation stage and interface board included in the ELL18K(/M) bundle are robust to general handling. To ensure reliable operation, keep the surface of the plastic track contacted by the motors free of oils, dirt, and dust. It is not necessary to wear gloves while handling the rotation stage, but avoid touching the track to keep it free of oils from fingerprints. If it is necessary to clean the track, it may be wiped with isopropyl alcohol or mineral spirits (white spirit). Do not use acetone, as this solvent will damage the plastic track.

The open frame format of the ELL18(/M) rotation stage can tolerate up to 8 kV of static discharge. ESD precautions should be taken, as an electrostatic discharge can produce an electrical signal that may cause an unintended movement of the stage. A bending load in excess of 500 g applied to the board may cause the PCB to deform, which will degrade the performance of the rotation stage. As readings from a magnetic sensor are used during the homing and positioning of the stage, avoid subjecting the structural PCB to excessive loads or magnetic fields. Limit the strength of magnetic fields in proximity to the magnetic sensor to ±5 mT to avoid negatively affecting the homing and positioning operations.

Mounting and Loading the Rotation Stage

The rotation stage can be mounted so the top surface of the stage is either in the horizontal or the vertical plane. There are four Ø4.2 mm (Ø0.17") through holes located along the edges of the board, which are visible in the image at the center-right of this tab, that may be used to mount the stage. For mounting the stage horizontally, the ELL18K(/M) rotation stage comes with two mounting brackets with slots for 1/4" (M6) screws. The rotation stage can be mounted to the brackets with the four included M3 screws. For vertical mounting, attach the rotation stage to the ELLA3 post mount adapter with the included four M4 screws. When mounting the stage, ensure that the installation does not bend the PCB.

Loads may be mounted to the stage using the 37 tapped holes for 8-32 (M4) threaded screws, whose spacing is shown in the diagram to the right. The maximum allowed weight of the mounted components is 200 g. The mounted load must be centered on the stage in order to achieve 200 g. In all cases of mounting and loading, ensure that nothing interferes with the moving parts of the rotation stage and that the stage and its load are securely fastened to prevent jostling during movement. Jostling of the stage or the load can cause an encoder error.

Supplying Power

When the setup includes the interface board, power may be supplied through the Micro-B USB connector and/or the 5 VDC power socket located on the board. The electronics on the interface board convert the applied DC signal to a sinusoidal signal oscillating at the required resonance frequency.

The ELL18K(/M) bundle includes a 5 VDC power supply whose connector mates with the power socket on the interface board. Delivering power through this socket also allows the Micro-B USB connector to be used for a computer to control the stage remotely. The power supplied by a computer through the USB 2.0 connection is not sufficient to power the stage. If computer control is not necessary, another option for supplying power to the stage is a portable USB 5 V battery pack connected to the Micro-B USB connector on the interface board.

When the implementation does not include the interface board, the connection with the power source is made using the pins on the Picoflex^® connector that is included on the rotation stage board. A pinout diagram of this connector is included in the Pin Diagram tab, and information on powering and addressing the rotation stage is given in the manual and the communications protocol manual, respectively.

Operation of the Motors

The motion of the rotation stage is controlled by forcing the piezoelectric elements to vibrate at specific ultrasonic frequencies. For each motor, there is one ultrasonic resonant frequency that will push the stage forward, and another that will pull the stage backward. Operating a motor at one of its resonance frequencies causes the tip of the motor to continuously cycle in a tight clockwise elliptical path. When the motor is driven at its other resonant frequency, the tip of the motor cycles through that same path in a counterclockwise direction. Both resonant frequencies are around 100 kHz. The total displacement at the tip of motor is a function of the mechanical load it is driving and the voltage supplied to the piezo element. In the case of no loading and a 5 V maximum driving voltage at a resonant frequency, the tip of the motor expands and contracts no more than a few microns while tracing the elliptical path. Please see The Elliptec^® Motor tab for more information and an animation illustrating the operational principle of the motors.

Homing the Rotation Stage

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The Interface Board

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Features of the Interface Board

To Home the stage, press the BW button on the interface board, click the Home button in the Elliptec software's graphical user interface (GUI) or send the appropriate ASCII message as is specified in the communications protocol manual.

The default Home position is referenced to a fixed feature on the stage assembly. If desired, the user may redefine the position of Home to be offset from the default position by up to +90° (a quarter turn in the clockwise direction). Being able to customize the Home position can be useful when synchronizing the orientations of two or more stages. When executing the Home command, the stage first finds the approximate location of Home, and then a fine-positioning procedure is used to orient the stage at Home with an accuracy of 288.0 µrad. The user can specify whether the stage rotates in a clockwise or counterclockwise direction (as defined from the perspective of looking down on the surface of the stage) during the first phase of the homing procedure, but the fine-positioning phase is always performed in the counterclockwise direction for repeatability.

Positioning the Rotation Stage

Note that the rotation stage is not intended for continuous operation. We recommend operation with duty cycles of less than 40% during general use, while operation with duty cycles greater than 60% should be limited to a few seconds.

Before the stage may be positioned, the Home position of the stage must be found. Please see the previous section for details. The movement of the stage may be controlled through computer control via the Elliptec^® software package that may be downloaded, or by sending simple signals to digital lines on the stage's board. A link to download the software and accompanying documentation can be found in the Software tab.

Multiple Elliptec devices can be be controlled using the ELLB Bus Distributor or by splicing multiple connectors onto one ribbon cable. A single bus distributor can connect up to four Elliptec devices; up to 16 devices can be connected if the buses are daisy chained. This bus can be controlled one of three ways: through an interface board (included with the bundles below) to connect to a PC running the Elliptec software, by connecting to an Arduino^® or Raspberry Pi^® board, or by wiring the connector pins to a user-supplied control board. Note that if an interface board is used, its on-unit buttons will be disabled. Alternatively, up to 16 devices can be spliced onto a single ribbon cord. The devices can then be simultaneously controlled by the interface board or selectively controlled by the Elliptec software. See the manual for instruction on how to splice multiple devices onto a ribbon cord and the Pin Diagrams tab for pin assignments when making custom connections. The communications protocol manual describes how to use the software to individually address each connected device. IA link to download the software and accompanying documentation can be found in the Software tab.

The default increment to move the stage forward and backward is 45°, and a custom increment can be set using the Elliptec software or by sending the appropriate ASCII message(s) as specified in the communications protocol manual. The Elliptec software can be used to move the stage to absolute and relative positions, in addition to jogging the stage forward or backward. The software is also used to set the jog step size, read the position of the stage, and adjust the position of Home, as is described in the previous section.

Readings from the magnetic sensor, which can resolve angular increments of 24.0 µrad, are used to position the stage and when executing the Home command. The travel range of the stage is not limited, but the reported orientation of the stage is always expressed as a value between 0° and 359.99°. The minimum incremental movement of the stage is 288.0 µrad, and it can be positioned with a repeatability of 434 µrad in response to signals from the magnetic sensor.

The stage learns to efficiently position itself precisely using a position error compensation algorithm. After the stage moves into a new position, it detects the error between the requested and actual positions. The position of the stage is then corrected, and an error compensation value is calculated. The algorithm is then updated with the error compensation value, so that it is applied when the stage is move to its next position. Typically, an optimum error compensation value is found after between two and six movements.

Resonance Frequencies

On power-up, the factory default setting instructs each motor driving the rotation stage to search for the resonance frequencies that will deliver the best performance. During this process, the rotation stage will translate a forward and backward by a small amount. If movement on start-up is undesirable, it is possible to disable this calibration procedure by using the serial port to initialize the frequencies on power-up. A new search for optimal resonance frequencies may be performed at any time; to maintain optimal performance, it is recommended that new searches be performed after changes in loading and/or ambient temperature. Please see the manual for details.

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The Elliptec Piezoelectric Resonant Motor Control Software GUI

Software for Devices Driven by Elliptec^® Piezoelectric Resonant Motors

All devices based on the Elliptec^® resonant piezo motor may be controlled by the Elliptec system software, which features an intuitive graphical user interface (GUI). The source code, in C# format, is included in software bundle available for download, and custom applications can be created in any language. The image at right shows a screen capture of the GUI, and the button that follows links to the download page.

Commands are entered in the Sequencer command / wait order section located at the center-left of the GUI. An example of a sequence of commands that might be sent to the device is "Aho0" to move to the rotation stage at address "A" to the home position in the clockwise direction, and then "Afw" to move the stage at address "A" forward by the jog increment. The command "As1" is used to perform the frequency search that will identify the optimal resonant frequencies, for the current operating conditions, for Motor 1 at adddress "A." 

Software

Version 1.6.3

Includes the Elliptec System Software, with an easy-to-use GUI. Also available for download is the Communications Protocol manual, which details the communication commands for the Elliptec software package.