SM2-Threaded Rotation Mount with Resonant Piezoelectric Motors

Thorlabs' Elliptec Technology for OEM


Click to Enlarge
Figure 1.1  ELL21 Mount with ELLA6 Grooved Adapter Plate

Features

• SM2-Threaded Rotation Mount for Ø2" or Ø50 mm Optics
• Ideal for OEMs and Applications Requiring Rapid and Precise Optic Rotation
• Micro-B USB and Picoflex^®1 Connectors for Control Signals
• Multi-Drop Serial Communication Protocol Supported
• Absolute Magnetic Encoder Used to Position Mount (Ideal for Light Sensitive Applications)
• Bus Distributor Facilitates Control of up to Four Elliptec^® Devices
• Moving World Adapters Attach Using M3 x 0.5 Taps for Additional Mounting Features:
  
  • ELLA6(/M) Adapter with Keyway for Fiber Alignment Accessories
  • ELLA7(/M) Adapter with SM1 Threads and Taps for 30 mm Cage Systems
  • ELLA8 Adapter with Five SM05-Threaded Holes for Mounted Filters/Optics
• ELLC2 Accessory Upgrade Pack Available Below

Driven by Thorlabs' Elliptec^® piezoelectric resonant motor technology, this rotation mount is designed to be a compact solution for applications requiring optic rotation. The rotation mount is offered as a standalone unit (Item #'s ELL21 and ELL21/M), or as part of a bundle (Item #'s ELL21K and ELL21K/M), which also contains an interface board for manual control of the mount, power supply, and cables for connecting the mount 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.

The rotating cell of each mount is internally SM2 (2.035"-40) threaded and includes two SM2RR retaining rings for mounting Ø2" or Ø50 mm optics. It is designed to be lightweight and compact, and the closed-loop operation provides rotation to specified orientations with a repeatability of 0.05°. The assembled components of the ELL21K(/M) bundle are shown in Figure 1.1, with key features labeled. Please see The Elliptec^® Motor tab for more information.

The moving world is also compatible with three adapter plates (sold separately) that offer a variety of mounting threads and bores for other applications. The ELLA6(/M) adapter has an array of mounting holes, 30 mm cage system compatibility, and a keyway for fiber accessories. The ELLA7(/M) adapter has similar mounting holes and cage system compatibility in addition to a central SM1 (1.035"-40) threaded bore. The ELLA8 adapter has five SM05 (0.535"-40) threaded ports for use with mounted filters and other optics, as well as a smooth Ø1/2" central bore.

The motors are highly dynamic and have no gearing. The tips of both motor housings are in firm contact with the plastic track at the base of mount, as can be seen in Figure 1.2. 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 mount 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 0.01 N·m combined torque exerted by the stationary arms of the motors.

The open frame format, versatility, and simplicity of this rotation mount 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.

Control
There are multiple options for powering, driving, and controlling this rotation mount, which are detailed in the Positioning the Rotation Mount section of the Operation tab. The mount 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 mount. When the interface board is used as an accessory to change the position of the mount, its status in the software is automatically updated.

Click to Enlarge
Figure 1.2  The components of the ELL21K Rotation Mount Bundle are shown connected and with key features labeled.

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	Ø1/2" Rotation Mount	Ø1" Rotation Mount	Ø2" Rotation Mount	Motorized Iris

Operation Notes

This tab contains information on handling, mounting, and operating the ELL21K(/M) Rotation Mount Bundle.

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

Click to Enlarge
Figure 4.2  The Rotation Mount, Back

Click to Enlarge
Figure 4.1  The Rotation Mount, Front

Handling

The rotation mount and interface board included in the ELL21K(/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 mount, 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.

ESD precautions should be taken, as an electrostatic discharge can produce an electrical signal that may cause an unintended movement of the mount. Limit the strength of magnetic fields in proximity to the magnetic sensor to ±5 mT to avoid negatively affecting positioning operations.

Mounting and Loading the Rotation Mount

The rotation mount may be mounted either vertically or horizontally. The Elliptec motors should be facing up if the mount is used horizontally. The mount has several mounting features that can be used with Thorlabs components or within a custom OEM assembly. Four 4-40 threaded holes on the back of the mount are spaced 60 mm apart for compatibility with our 60 mm cage system. Each mount also features an 8-32 (M4 x 0.7) tap for post mounting and 1/4" bores for horizontal mounting on a table surface. There are also two Ø6 mm through holes for ER rods and close proximity mounting of two devices. Two additional 6.5 mm deep blind holes for ER05 cage rods ensure alignment of mounts in close proximity.

Click for Details
Figure 4.3  The rotation mount can be mounted in a 60 mm cage system using the 4-40 threaded holes on the back.

Click for Details
Figure 4.4  The rotation mount can be post-mounted and ER cage rods holes allow two mounts to be aligned in close proximity.

Click to Enlarge
Figure 4.5  Features of the Rotation Mount

The maximum allowed weight of the mounted optic is 100 g when mounted vertically and 300 g when mounted horizontally. The load must be centered on the mount in order to achieve these values. In all cases of mounting and loading, ensure that nothing interferes with the moving parts of the rotation mount and that the mount 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 ELL21K(/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 mount remotely. The power supplied by a computer through the USB 2.0 connection is not sufficient to power the mount. If computer control is not necessary, another option for supplying power to the mount is a CPS1 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 mount board. A pinout diagram of this connector is included in the Pin Diagram tab, and information on powering and addressing the rotation mount is given in the manual and the communications protocol manual, respectively.

Click to Enlarge
Figure 4.6  The Interface Board

Click to Enlarge
Figure 4.7  Features of the Interface Board

Operation of the Motors

The motion of the rotation mount 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 mount forward, and another that will pull the mount 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.

Positioning the Rotation Mount

Note that the rotation mount 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.

The movement of the mount 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 mount's board. A link to download the software and accompanying documentation can be found in the Software tab.

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^® 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. A link to download the software and accompanying documentation can be found in the Software tab.

The default increment to move the mount forward and backward is 10°, 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 mount to absolute and relative positions, in addition to jogging the mount forward or backward. The software is also used to set the jog step size, read the position of the mount, and adjust the position of Home, as is described in the previous section.

Readings from the magnetic sensor, which can resolve angular increments of 0.0055° (96 µrad), are used to position the mount and when executing the Home command. The travel range of the mount is not limited, but the reported orientation of the mount is always expressed as a value between 0° and 359.99°. The minimum incremental movement of the mount is 0.0055° (96 µrad), and it can be positioned with a repeatability of 0.05° (0.87 mrad) in response to signals from the magnetic sensor.

Resonance Frequencies

On power-up, the factory default setting instructs each motor driving the rotation mount to search for the resonance frequencies that will deliver the best performance. During this process, the rotation mount 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.

Click to Enlarge
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 1.6.5 (May 6, 2025)

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.