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28 mm Linear Stage with Resonant Piezoelectric Motors
Stage Bundle and Interface Board
Direction of Travel
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The components of the ELL17K(/M) linear stage bundle are shown connected and with key features labeled.
Driven by Thorlabs' Elliptec™ piezoelectric resonant motor technology, this linear stage is designed to be a compact solution for OEM applications requiring linear movement. Thorlabs offers the ELL17K(/M) linear stage bundle containing the ELL17(/M) stage, an interface board for manual control of the stage, a 5 VDC power supply, a ribbon cable for connecting the stage to the interface board, and a USB cable for connecting the interface board to a PC. The ELL17(/M) stage can be purchased individually.
Each stage has one center 8-32 (M4) tapped hole for attaching a single component and the four 4-40 (M3) tapped holes may be used to secure an adapter plate, such as the MMP1(/M) or RB13P1(/M).The stage is lightweight and compact with a mass of 0.052 kg and footprint of 68.0 mm x 67.0 mm when the stage is centered. The full travel range of the stage requires 7.5 mm of clearance on either side. The closed-loop operation allows the translating platform to be positioned with an accuracy of 100 µm and a repeatability of 60 µm. The assembled components of the ELL17K(/M) are shown in the image to the right, with key features labeled.
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 linear 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 1 N combined force exerted by the stationary arms of the motors. Please see The Elliptec™ Motor tab for more information.
The open frame format, simplicity, and adaptability of this linear stage make 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.
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.
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Components of the ELL17K(/M) Bundle
(One Region-Specific Power Adapter Included with the Power Supply)
As shown in the image above, a mounting bracket is included with the bundle. The bracket fastens to the underside of the linear stage's PCB with the four included screws. Two slots in the bracket align with the Ø11.0 mm (Ø0.43") holes at either side of the PCB, so that 1/4"-20 (M6) cap screws can be inserted through the holes in the PCB to secure the linear stage board to optical tables and breadboards. The bracket adds 5.0 mm of thickness to the profile of the stage. The drawing below shows the dimensions and mounting features of the stage itself.
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Mechanical Drawing of the Linear Stage
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Mechanical Drawing of the Interface Board
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Pinout diagram of the Picoflex® connector is shown referended to a partial diagram
of the Linear Stage Board. The polarity indicator on the connector
must be adjacent to the red wire on the supplied 8-connector cable.
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Pinout diagram of the Picoflex® connector is shown referenced to a simplified diagram
of the ELLB Bus Distributor. The polarity indicator on the connector
must be adjacent to the red wire on the supplied 8-connector cables.
This tab contains information on handling, mounting, and operating the ELL17K(/M) Linear Stage Bundle.Contents
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The Linear Stage (Without the Bracket)
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Features of the Linear Stage
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The Interface Board
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Features of the Interface Board
The linear stage and interface board included in the ELL17K(/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 linear 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 ELL17(/M) 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 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 linear 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.
The linear stage can be operated with the top surface of the stage in the horizontal or the vertical plane. If the latter is chosen, orient the stage so that it moves side to side rather than up and down. A mounting bracket included with the ELL17K(/M) fastens to the underside of the linear stage's PCB with the four included screws. Two slots in the bracket align with the Ø11.0 mm (Ø0.43") holes at either side of the PCB, so that 1/4"-20 (M6) cap screws can be inserted through the holes in the PCB to secure the linear stage to an optical table or breadboard. Alternately, the bracket can be omitted and the four slotted holes in the PCB used to attach the stage to a custom fixture. Ensure that electrically conductive structures are not in contact with the back of the board, as this may cause electrical shorts detrimental to the operation of the stage. When mounting the stage, ensure that the installation does not bend the PCB.
Loads may be mounted to the stage using the 8-32 (M4) or four 4-40 (M3) tapped holes at the center. The spacing of the 4-40 (M3) tapped holes is designed to be compatible with adapter plates such as the MMP1(/M) and RB13P1(/M), as shown in the image to the upper right. The maximum allowed weight of the mounted components is 200 g. In all cases of mounting and loading, ensure that nothing interferes with the moving parts of the linear 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.
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 ELL17K(/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 linear stage board. A pinout diagram of this connector is included in the Pin Diagram tab, and information on powering and addressing the linear stage is given in the manual and the communications protocol manual, respectively.
The motion of the linear stage is controlled by forcing the piezoelectric elements to vibrate at specific ultrasonic frequencies. For each motor, there is an 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 the 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 by 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.
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 stage uses a relative (incremental) magnetic sensor with an encoder resolution of 0.98 µm to home and position the stage. During the procedure to define the default Home position, the stage is translated forward and backward to index the limits of travel. The default Home position is located at the backward limit of the stage's range of motion. If desired, the user may redefine the position of Home to be offset from the default position. Being able to customize the Home position can be useful when synchronizing the orientations of two or more stages.
Note that the linear 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 by pressing buttons on the interface board, 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. The buttons on the interface board can be seen in the image of the interface board above. A link to download the software and accompanying documentation can be found in the Software tab. The interface board may be used as an accessory while interfacing with the stage through the Elliptec software; all changes in the position of the linear stage that occur as a result of pressing buttons on the interface board are registered by the software, and the software may independently control the linear stage while the interface board is connected.
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. A link to download the software and accompanying documentation can be found in the Software tab.
The interface board can be used to move the stage forward and backward in increments by pressing and holding the JOG button while pressing and releasing the FW or BW button, respectively. The default increment is 2 mm, and a custom step size 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. The velocity of the stage can be adjusted to a value equal to or greater than 60% of the maximum velocity through use of the ASCII message calls described in the communications protocol manual.
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.
On power-up, the factory default setting instructs each motor driving the linear stage to search for the resonant frequencies that will deliver the best performance. During this process, the linear stage will translate forward and backward. 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 resonant 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 Components of the Elliptec Motor
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The Elliptec Piezoelectric Resonant Motor
The Elliptec™ Piezoelectric Resonant Motor
Thorlabs' Elliptec™ piezo resonant motor, shown at right, is lightweight, with a mass of 1.2 g, and compact: the dimensions of the resonator housing, excluding the spring, are 8 mm x 4 mm x 20 mm.
Components of the Motor
The components that compose the motor are shown at far-right. The piezoelectric element is press fit into the aluminum resonator, which has been precisely designed and machined to produce the desired elliptical motion at the tip and to interface optimally with the driven module. The free ends of the spring are integrated with the resonator housing. The wires, which are soldered to the top and bottom of the piezoelectric element, deliver the voltage signal that induces the piezoelectric element to vibrate at ultrasonic frequencies.
When the motor is built into a system, the open loop of the spring is bolted to a sturdy surface that is stationary with respect to the item to be driven, and the tip of the resonator is placed in contact with the item. The purpose of the spring is to maintain constant contact between the tip of the resonator and the driven item, and the direction of motion is determined by the resonance frequency at which the piezo element is driven.
Elliptical Motion and Comparison with Conventional Motors
Elliptec motors quickly and precisely position stages and mounts while never seeming to move. Their microscopic movements occur at ultrasonic frequencies and are invisible to the naked eye.
The motor is operated by driving it at one of its two resonance frequencies. A voltage signal oscillating at an ultrasonic frequency is applied to the piezoelectric chip, which responds by expanding less than a micron and then contracting back to its original dimensions at the frequency of the driving signal. This rapid-cycling change in the chip's dimensions causes a vibration in the aluminum resonator housing. When the vibration is at one of the housing's resonance frequencies, a pushing motion results at the tip of the motor. When the vibration is at the other resonance frequency a pulling motion results.
As illustrated in the video, the pulling and pushing motions result from the tip of the motor tracing an elliptical path in space when the motor operates at resonance. The selected resonance frequency controls the direction of the cyclical motion. The motor's tip traces one half of the ellipse as it expands and the other half as it contracts. When the motor pushes the driven item, the motor's tip is in contact with the item while the tip expands; the two are not in contact while the tip contracts. The converse is true when the motor pulls the driven item in the opposite direction. The total displacement at the tip of the motor is a function of both the mechanical load it is driving and the voltage supplied to the piezo element. The maximum displacement can be up to a few microns when the peak driving voltage is 5 V.
The motor behaves in many ways like a DC or electromagnetic stepper motor, but it does not suffer from many of the drawbacks of these conventional motors. Unlike conventional electromagnetic motors, which must overcome inertial delays to come to a stop, the highly dynamic Elliptec motor can stop within microseconds. As it has no gears, it does not exhibit backlash. Since it possesses no magnets, it is compatible with use in environments sensitive to electromagnetic interference. The motion of the driven element is continuous and smooth. As the tip of the motor must be in contact with the driven item to induce motion, the motor possesses the safety feature of an inherent friction brake. When in contact with a plastic surface, the motor operates virtually silently.
For OEM applications, the motor can be manufactured in volume at low cost, and it can be driven by inexpensive analog electronics. It does not require microprocessors or software; however it is compatible for use with them.
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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 "Agj" to get the jog step size of the stage at address "A," "Asj0000200" to set the jog step size as 0.25 mm, and "Abw" to jog the stage at address "A" backward by 0.25 mm. 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."
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The motors' aluminum tips contact the black plastic strip at the edge of the linear stage to translate the stage back and forth.
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The Linear Stage Bundle is a complete package that includes a linear stage and an interface board, which facilitate quick integration into laboratory setups and other experimental applications. It also provides a convenient means to evaluate incorporating this technology into OEM applications.
A mounting bracket included with the bundle fastens to the underside of the linear stage's PCB with four included screws. Two slots in the bracket align with the Ø11.0 mm (Ø0.43") holes at either side of the PCB, so that 1/4"-20 (M6) cap screws can be inserted through the holes in the PCB to secure the linear stage board to optical tables and breadboards. The bracket adds 5.0 mm of thickness to the profile of the stage.
This linear stage is offered individually to meet the needs of applications whose designs require multiple networked Elliptec resonant motor products, or applications that do not require the other components included in the bundle above.
The ELL17 Linear Stage has a 28 mm travel range and a mounting surface featuring a center 8-32 (M4) tapped hole and four surrounding 4-40 (M3) tapped holes. Components may be mounted directly to the stage, or the 4-40 (M3) tapped holes can be used to secure an adapter plate, such as MMP1(/M) or RB13P1(/M), as a mounting surface. Please contact us to discuss customizing the stage, or to arrange to purchase a mounting bracket with the stage.
The PCB of the linear stage incorporates a male 8-pin Picoflex® connector (header). Each ELL17 stage ships with the female 8-pin Picoflex® connector (receptacle) that mates with the connector (header) on the board.
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A single bus distributor can be used to control up to four Elliptec devices. The bus can be connected to a PC using the interface board provided with the bundles sold above. Note that the bus is then controlled by the Elliptec software and that the buttons on the interface board are disabled.
The ELLB Bus Distributor connects up to four Elliptec™ devices. Connected devices can be controlled with or without the interface board included with the above bundles. When using the interface board, each connected device is controlled remotely by a PC running the Elliptec software package. The interface board connects to the bus's input port labeled REMOTE; once connected, the interface board's buttons are disabled. For control without using the interface board, see the Pin Diagrams tab for custom connections.
Multiple ELLB Bus Distributors can be daisy chained to control and power up to 16 Elliptec devices; simply connect one of the four MODULE outputs to the second board's REMOTE input. Indicator LEDs are provided to show which device is active. 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 bus includes a Ø6.3 mm power connector that supports a 5 V supply with a maximum current of 4 A. As more devices are connected, simultaneous control of the units will require more current to be provided by the power supply; please see the Specs tab for the amount of current drawn by each Ellitpec device. Power supply options provided by Thorlabs include the TPS101 5 V, 2 A power supply and the 5 V, 1 A supply included with the above bundles. Depending on the current draw of the Elliptec devices connected, these supplies provides enough current to power two devices simultaneously.
Fourteen control pins, detailed in the image to the right, are included for additional functionality. Four pairs of pins are each shorted with a jumper that, when in place, enables the Elliptec software to receive feedback from connected Elliptec devices. The pair of pins labeled LED is shorted with a jumper that, when removed, will disable the indicator LEDs. The 5V and GND allow an optional, user-provided 5 V, 2 A power supply to be used in place of a source connected to the Ø6.3 mm power connector. The RX and TX pins can be used to control the bus with a Raspberry Pi® or Arduino® board, respectively, instead of the Elliptec interface board.
The board is mounted using the Ø3.5 mm through holes provided in each corner. Four 8-conductor, 28 AWG ribbon cables are included.