Linear Encoders - Motion Control Tips

FAQ: How do I pick between rotary and linear encoders?

June 24, 2016 By Lisa Eitel Leave a Comment

Edited by Zak Khan || It may seem as though linear encoders and rotary encoders have strictly defined (and maybe even mutually exclusive) applications. Prevailing logic is that linear encoders track linear motion and rotary encoders track rotating shafts — but this isn’t always the case.

Some motion designs can use linear or rotary encoders, so engineers can pick between the two. Elsewhere, designs with multiple kinds with of motion might benefit from multiple actuators on both linear and rotary axes to monitor key machine sections. Engineers should identify the locations of all potential faults of a machine and pick encoders that can detect those for the controller in some way. Some installations excel when a machine uses both linear and rotary encoders.

Read more about linear encoders —
including various ways to measue linear distances, how linear encoders improve accuracy, the first consideration in choosing a linear encoder, and IoT functionality with linear encoders — at linearmotiontips.com/category/linear-encoders.

Example encoder application: Milling machine

Consider a milling machine that moves linearly to position itself over raw material — and rapidly rotates a drill to bore holes. Because two types of motion are present, there are two points at which an encoder can track the machine’s material removal. More after the jump.

Two encoder options are to either measure output-axis motion through the ballscrew shaft with a rotary encoder or directly measure linear motion through a linear encoder. Some applications — such as a milling machine, for example — need the latter. That’s because one rotary encoder can’t compensate for thermal expansion (top image). Here, a linear encoder also helps track any displacement (bottom image). Image courtesy Heidenhain.

Using a rotary encoder means the encoder mounts on the machine’s threaded tool rod to track both linear displacement (by changes in thread pitch) and rotary position. In this particular setup, tracking rotary motion is subject to thermal drift that can cause position loss. As the machine operates, friction from material cutting heats the rod. This distorts linear position tracking because the rod expands, as the rotary encoder can’t compensate for this effect (because again, it only tracks rotary displacement and thread pitch). As these two factors don’t change with thermal effects, the encoder continues to report the same linear position.

In contrast, using a linear encoder means that the controls track the X-Y position of the drill over the raw material. Here, the linear encoder accounts for thermal expansion through measurements of linear displacement, so controls can compensate for induced errors.

Other designs where linear and rotary encoders work

Linear and rotary encoder applications overlap in other designs. Consider a conveyor belt driven by a motor. Here, a rotary encoder can track the motor even if the latter misses steps or stalls. One caveat: If the conveyor slips or breaks, the motor might continue operating as if nothing occurred. Here, a linear encoder keeps better track of the whole conveyor system — sending feedback to the controller of conveyor motor faults as well as conveyor belt faults.

In other words …

… an application using a drive belt can use a rotary encoder on an idle roller to detect faults, as that location would let the encoder detect the ceasing of rotary motion.

In contrast, a rotary encoder mounted on the drive roller of a similarly arranged conveyor might not work so well. That’s because if the belt failed, the roller to which the encoder mounts would still spin. Here, an alternative is a linear encoder to track the conveyor to detect an loss of motion.

Thank you to Kathleen Stoneski representing Heidenhain Corp. for information in this article.

FAQ: What are the ways to wire an absolute encoder into a motion system?

November 19, 2015 By Danielle Collins Leave a Comment

Absolute encoders can be wired in one of three ways: in parallel, with a serial interface, or over a bus. The serial and bus interfaces have multiple protocols or standards, some of which are open-source, while others are proprietary to specific manufacturers. When considering how to wire an absolute encoder, the required resolution, level of application control, flexibility, and ease of implementation all factor into the decision.

Parallel wiring

Wiring an encoder is parallel is the most straightforward method and is the standard for single-turn encoders. In parallel wiring, the encoder is connected directly to the receiving device. Each wire handles just one data bit, which means that the more bits of resolution an encoder has, the more wires are required. For high-resolution devices, this can become burdensome and costly—particularly for multi-turn encoders, which have higher bits per turn and multiple turns.

Parallel wiring often provides output in a modified version of binary code, known as reflected binary code, or Gray code (named for Frank Gray, the researcher who developed it). Standards binary code presents a problem for data transmission, because some steps involve changes in more than one bit (digit). For example, from step 3 to step 4, binary code changes from 0011 to 0100, with three bits changing state. Because it is impossible for the bits to change at exactly the same time, a false reading of the output could be taken. Gray code avoids this problem by changing only one bit at each step.

Gray code avoids the potential for error that arises when more than one bit changes state in a given step.

Because it uses one wire per bit, parallel wiring is best for simple implementations. Distance is also limited to less than 10 meters, due to the potential for noise interference. It is, however, a very fast communication method, with all the data available in real time, all the time.

Serial interface

The serial wiring scheme provides point-to-point communication from a master, such as a PLC or micro controller, to a slave, which, in this case, is an encoder. There are several serial interfaces, with SSI (Synchronous Serial Interface) being the most common, particularly in Europe, while BiSS (Bidirectional Synchronous Serial Interface) is relatively new. EnDat is a proprietary interface developed by Heidenhain. The main benefit of EnDat is that it provides for internal memory in the encoder and can carry more information than SSI. Similarly, HIPERFACE is a proprietary interface developed by Max Stegmann GmbH, which provides absolute position information at start-up, and then provides incremental encoder data after that. Both BiSS and HIPERFACE can be connected either point to point or via bus. Each of these interfaces, with the exception of HIPERFACE, uses synchronous data transmission, in which the transfer of data is managed by synchronized clocks in the transmitting and receiving devices.

Serial communication is a good choice for applications with too many outputs for parallel wiring to be practical, but to few to justify a bus communication. As a benefit, serial communication works over longer distances than parallel or bus wiring schemes—sometimes over 1000 meters. However, because serial wiring schemes are point-to-point, there are limits to the number of nodes (devices) that can be included in a network.

Comparison of serial interfaces
Image credit: Danaher Industrial Controls

Bus interface

A bus interface allows the encoder to communicate with other devices on the network on a peer-to-peer basis, and is also known as a ring topology. Two common bus protocols are DeviceNet and Profibus. Profibus was developed by the European Community and is, in general, more popular in Europe, while DeviceNet was developed by Allen Bradley (now part of Rockwell Automation), and is generally more common in the U.S.

Because more than one device can be connected to a single controller, bus interfaces use fewer cables than other wiring types in most applications. They also perform well over longer distances—typically up to 100 meters. However, the network topology is generally more complex, and the individual components are more expensive. Regardless of the up-front cost of a bus interface, the total cost of the system can be less than other wiring methods, due to fewer cables being required and, in turn, less setup and troubleshooting time needed.

FAQ: How do magnetic encoders work?

November 13, 2015 By Danielle Collins Leave a Comment

Encoders, whether rotary or linear, absolute or incremental, typically use one of two measuring principles—optical or magnetic. While optical encoders were, in the past, the primary choice for high resolution applications, improvements in magnetic encoder technology now allow them to achieve resolutions down to one micron, competing with optical technology in many applications. Magnetic technology is also, in many ways, more robust than optical technology, making magnetic encoders a popular choice in industrial environments.

Magnetic rotary encoders

Magnetic rotary encoders rely on three main components: a disk, sensors, and a conditioning circuit. The disk is magnetized, with a number of poles around its circumference. Sensors detect the change in magnetic field as the disk rotates and convert this information to a sine wave. The sensors can be Hall effect devices, which sense a change in voltage, or magnetoresistive devices, which sense a change in magnetic field. The conditioning circuit multiples, divides, or interpolates the signal to produce the desired output.

The resolution of a magnetic rotary encoder is determined by the number of magnetic poles around the disk and by the number of sensors. Incremental encoders (whether magnetic or optical) use quadrature output and can employ X1, X2, or X4 encoding to further increase resolution. The primary difference between incremental and absolute encoders, regardless of sensing technology, is that absolute versions assign a unique binary code, or word, to each measuring position. This allows them to track the encoder’s exact position, even if power is discontinued.

Rotary magnetic encoder
Image credit: ams AG

Linear magnetic encoders

The operation of linear magnetic encoders is analogous to their rotary counterparts, except that they use a linear scale (also referred to as a tape, since they typically have an adhesive backing) and a read head. The read head can employ either a Hall effect or a magnetoresistive sensor, and detects signals generated by the magnetic code on the scale to provide position information. For absolute linear magnetic encoders, each position on the scale represents a unique binary word, indicating the exact linear position of the read head. For incremental versions, one or more reference marks are included on the scale, to enable homing after a power-off situation. Linear magnetic scales can be provided in very long lengths—up to 100 meters from some manufacturers.

Linear magnetic encoder
Image credit: ams AG

The most significant advantage of magnetic encoders may be their robustness. Unlike optical encoders, magnetic versions are insensitive to contaminants such as dust, dirt, liquids, and grease, as well as to shocks and vibrations. Similar to optical encoders, magnetic encoders do require an air gap between the magnetic disk and the sensor. However, the air gap in a magnetic encoder does not need to be clean and transparent, as it does for an optical encoder. As long as no ferrous material is present between the disc and the sensor, the magnetic pulses will be detected. Two important specifications for proper operation of magnetic encoders are the radial placement of the sensor in respect to the disk (or tape), and the gap distance between the sensor and the magnet.

Feature image credit: Dynapar

FAQ: What are capacitive encoders and where are they suitable?

October 29, 2015 By Danielle Collins 1 Comment

Two types of encoders dominate the general industrial market—optical and magnetic. But capacitive encoders, a relatively new introduction, offer resolution comparable to optical devices, with the ruggedness of magnetic encoders. Currently, there are only a handful of vendors for capacitive encoders, but their suitability for applications requiring high precision and durability make them a good choice for the semiconductor, electronics, medical, and defense industries.

Why capacitive encoders over optical or magnetic?

While optical encoders can deliver high resolution, their main components—an optical disk, an LED light source, and photo-detectors—are fragile and highly sensitive to dust, dirt, and other environmental contamination. They can also be damaged by vibrations and require a relatively stable temperature range. Magnetic encoders, on the other hand, are quite robust, but provide lower resolution than optical encoders. They are also sensitive to magnetic interference, which is a notable concern when used with stepper motors.

Probably the most important difference between optical and capacitive encoders is that capacitive encoders don’t require an optical disk. This makes capacitive versions more robust, less susceptible to contamination and less influenced by temperature variations than optical encoders are. And with no LED to burn out, capacitive encoders can achieve a much longer life than optical versions. They are also more efficient, with current consumption typically less than 10 mA—as compared to the 20 mA or higher consumption of an optical encoder. This is especially beneficial in applications where power is supplied via a battery. Another benefit of capacitive encoders is the ability to change the encoder’s resolution by modifying the line count in the electronics, without changing components. Compared to magnetic encoders, capacitive versions simply provide better resolution in most situations, and can be produced at a lower cost. More after the video jump.

How capacitive encoders work

The basic principle behind capacitive encoders is that they detect changes in capacitance using a high-frequency reference signal. This is accomplished with the three main parts—a stationary transmitter, a rotor, and a stationary receiver. (Capacitive encoders can also be provided in a “two-part” configuration, with a rotor and a combined transmitter/receiver.) The rotor is etched with a sinusoidal pattern, and as it rotates, this pattern modulates the high-frequency signal of the transmitter in a predictable way.

The receiver disk reads the modulations, and on-board electronics — a proprietary ASIC is used by the vendor CUI, Inc. — translate them into increments of rotary motion. The electronics also produce quadrature signals for incremental encoding, with resolution ranging from 48 to 2,048 pulses per revolution (PPR).

capacitive-encoder-principle-of-operation

Capacitive encoders work by transmitting a high-frequency signal through a rotor that is etched with a sinusoidal pattern. As the rotor moves, this pattern modulates the signal in a predictable way. The receiver reads the modulations, and on-board electronics translate them into increments of rotary motion.
Image credit CUI Inc.

In the proprietary capacitive Electric Encoder by Netzer Precision Motion Sensors, the encoder has two operating modes: Coarse Mode and Fine Mode. Coarse Mode is typically used upon system start-up, to determine the initial position. The encoder is then switched to Fine Mode for ongoing operation. By breaking up the total measuring range into small, equal, distinct segments, the scale of each segment can be much finer than if the same scale were used over the entire measuring range. This enables very high resolution without added expense.

Left: A three-part capacitive encoder with a stationary transmitter, a rotor, and a stationary receiver.
Right: A two-part capacitive encoder with a combined transmitter/receiver, and a rotor.
Image credit: Netzer Precision Motion Sensors Ltd.

The primary concern when using capacitive encoders is their susceptibility to noise and electrical interference. To combat this, the ASIC circuitry must be carefully designed and the algorithms for de-modulation must be fine-tuned. Capacitive technology, however, has been used for many decades in digital calipers and is well-proven. Now it is making its way into the encoder product space, where it provides high resolution without sacrificing robustness.

Feature image credit: CUI Inc.

FAQ: What do X1, X2, and X4 position encoding mean for incremental encoders?

October 1, 2015 By Danielle Collins Leave a Comment

An encoder is a device that measures position, and in some configurations, can also measure direction. Rotary encoders measure rotation of a shaft, while linear encoders measure distance traveled. For both types of encoder, the position measurement can be either incremental or absolute. An incremental encoder measures change in position, but does not keep track of actual position. When power is interrupted, incremental encoders lose their position reference and must start over via a re-homing sequence to a reference point. Absolute encoders, on the other hand, keep track of absolute position, whether rotation of a shaft or linear travel, by assigning a unique digital value to each position. So even if power is lost, an absolute encoder will know the exact position of the shaft or the linear drive.

Incremental encoders work by producing a specific number of equally spaced pulses per revolution (PPR) or per distance (PPM—pulses per millimeter, or PPI—pulses per inch). When one set of pulses, or output channel, is used, the encoder can determine position only. But most incremental encoders use quadrature output, which consists of two channels, typically referred to as channel A and channel B, that are out of phase by 90 degrees. Quadrature output allows the encoder to also sense direction, by determining which channel is leading and which is following. Some incremental encoders also produce a third channel with a single pulse, commonly referred to as channel Z or channel I. This channel serves as the index or reference position for homing.

With quadrature output, three types of encoding can be used: X1, X2, or X4. The difference between these encoding types is simply which edges of which channel are counted during movement, but their influence on encoder resolution is significant.

With X1 encoding, either the rising (aka leading) or the falling (aka following) edge of channel A is counted. If channel A leads channel B, the rising edge is counted, and the movement is forward, or clockwise. Conversely, if channel B leads channel A, the falling edge is counted, and the movement is backwards, or counterclockwise.

X1 encoding, in which either the rising or the falling edge of channel A is counted. Notice that when channel B is leading, the movement is considered counterclockwise or reverse, and the count is decreased.
Image credit: National Instruments Corporation

When X2 encoding is used, both the rising and falling edges of channel A are counted. This doubles the number of pulses that are counted for each rotation or linear distance, which in turn doubles the encoder’s resolution.

X2 encoding, in which both the rising and falling edges of channel A are counted.
Image credit: National Instruments Corporation

X4 encoding goes one step further, to count both the rising and falling edges of both channels A and B, which quadruples the number of pulses and increases resolution by four times.

X4 encoding, in which both the rising and falling edges of channels A and B are counted.
Image credit: National Instruments Corporation

For rotary encoders, position is calculated by dividing the number of edges counted by the product of the number of pulses per revolution and the encoding type described above (1, 2, or 4), and then multiplying the result by 360 in order to get degrees of motion.

x = type of encoding (X1, X2, or X4)

N = number of pulses generated per shaft revolution

For linear encoders, position is calculated by dividing the number of edges counted by the product of the number pulses per revolution and the encoding type. This result is then multiplied by the inverse of the pulses per millimeter (or per inch).

PPM = pulses per millimeter

PPI = pulses per inch

Incremental encoders are a relatively simple and inexpensive feedback option for applications where re-homing after a power loss is not detrimental to the process. And with quadrature output, incremental encoders can achieve high resolution, even at high speeds.

Featured image credit: National Instruments Corporation

Linear encoder types — and parameters for selection

September 25, 2015 By Danielle Collins 2 Comments

Linear encoders monitor linear movement and provide position feedback in the form of electrical signals. In servo driven systems, linear encoders supply the precise position of the load, typically in addition to the speed and direction feedback provided by the motor’s rotary encoder. For stepper driven systems, which typically operate in open-loop mode with no position feedback, adding a linear encoder increases the accuracy and reliability of the positioning system without the cost and complexity of a servo motor.

Linear encoder feedback: Absolute or incremental

When selecting a linear encoder, the first thing to consider is what type of feedback is needed for the application—absolute or incremental. Absolute encoders assign a unique digital value to each position, which allows them to maintain precise position information, even when power is lost.

Feature image credit: Renishaw

Incremental encoders work by generating a specific number of pulses per unit of travel and counting those pulses as the load moves. Because they are simply counting pulses, incremental encoders will lose their position reference if the power supply is interrupted. In order to determine the load’s actual position upon startup or re-start, a homing sequence is required. This means that the sensor (and the load) must move to a reference position, and from there it can begin to determine the load’s position. Keep in mind that even if the load’s actual position at startup or re-start is not critical, performing a homing sequence may be undesirable from a time and productivity standpoint. This is especially important in applications with long strokes and slow speeds, such as machine tools, where homing can be a time-consuming process.

The output for absolute and incremental encoders differs and is also a consideration for integration into the system’s control scheme. Absolute linear encoders produce a digital output, or “word,” that signifies the unit’s actual position. Resolution for an absolute encoder is determined by the number of bits in the word.

Incremental encoders produce quadrature output, with two channels that are 90 degrees out of phase. (The two channel output allows both position and direction to be monitored. If only position is needed, then only one channel is used.) Some incremental encoders produce a third channel with a single pulse, to be used as the index or reference position for homing. The number of pulses per distance (inch or millimeter) determines the resolution of an incremental encoder. However, resolution can be doubled by counting both the leading and trailing edges of the pulse from one channel, or it can be quadrupled by counting the leading and trailing edges of the pulses from both channels.

Quadrature output for an incremental encoder. Channels A and B are out of phase by 90 degrees. Channel Z has one pulse, used as a reference for homing.

Linear encoder technology: Optical or magnetic

Once the decision has been made regarding incremental or absolute feedback, the next consideration is whether the sensing technology should be optical or magnetic. While optical encoders have historically been the only option for resolutions below 5 microns, improvements in magnetic scale technology now allow them to achieve resolutions down to 1 micron.

Optical encoders use a light source and a photo-detector to determine position, but their use of light makes them sensitive to dirt and debris, which can disrupt the signal. The performance of optical encoders is highly influenced by the gap between the sensor and the scale, which must be properly set and maintained to ensure that signal integrity is not compromised. This means that mounting must be done carefully, and shocks and vibrations should be avoided.

Optical linear encoder with absolute feedback.
Image credit: Heidenhain

Magnetic encoders use a magnetic reader head and a magnetic scale to determine position. Unlike optical encoders, magnetic encoders are mostly unaffected by dirt, debris, or liquid contamination. Shocks and vibrations are also less likely to affect magnetic encoders. They are, however, sensitive to magnetic chips, such as steel or iron, as they may interfere with the magnetic field.

Magnetic linear encoder with incremental feedback.
Image credit: Balluff Inc.

While linear encoders are often an add-on component to a system, in many cases their benefits outweigh the additional labor and cost. For example, in ball screw driven applications, a lower accuracy screw can be chosen if a linear encoder is used, since the encoder feedback allows the controller to compensate for positioning errors introduced by the screw.

Read more about linear encoders —
including various ways to measure linear distances, how linear encoders improve accuracy, the first consideration in choosing a linear encoder, and IoT functionality with linear encoders — at linearmotiontips.com/category/linear-encoders.

Feature image credit: Renishaw

Programmable Encoders: The Next Generation

August 20, 2015 By Motion Control Tips Editor Leave a Comment

by Jarrod Orszulak, Product Manager, POSITAL-FRABA

The latest programmable encoders offer both incremental and absolute functionality on one hardware platform and can be programmed with a WiFi connection.

Programmable incremental encoders have become more common recently. This is largely due to the fact that the measurement characteristics of the device (number of pulses per rotation, output level and so on) can be modified through a software update without requiring any changes to physical components. Now, however, engineers at POSITAL have taken the programmability concept to a new level with the new generation of iXarC rotary encoders. These new encoders offer both incremental and absolute encoder functions on a single hardware platform; are available in a range of mechanical configurations and connector types; are supported by a range of configuration management tools that can be accessed by end users over the full working life of the encoder; and can be programmed by any WiFi-enabled electronic device.

A new generation of programmable encoders offers a lot more flexibility for users, providing both incremental and absolute encoder functions on a common hardware platform, as well as programming through WiFi.

Of course, programmable encoders are not new. For instance, a traditional programmable encoder can allow users to program basic encoder parameters such as the resolution or the electronic interface level. Then there’s the method of programming itself. The simplest method may be with mechanical DIP switches. Others methods include using a simple serial interface such as USB or part of an integrated system connected with a PLC or HMI. What is new with these latest encoders is the kind of programmability as well as the way they are programmed.

Benefits of programmable encoders
Encoders are used to monitor position and motion within machines in many different industries. They are an essential interface between the mechanical components and the control system of a machine, so that functional requirements are as diverse as the range of applications. This diversity has led to a huge variety of available incremental and absolute encoders.

With programmable encoders, much of the variety in measurement characteristics can be accommodated through software changes so that the range of hardware devices needed is significantly reduced. Distributors or system integrators can stock a limited number of hardware versions and still meet customer requirements quickly and efficiently. This means that users and distributors can reduce their stock levels and spare-parts inventories significantly. Prior to delivery or installation, the encoder’s measurement characteristics can be set up quickly. Moreover, the same device can be easily updated at some future time if the machine is changed or upgraded.

Once the encoder has been configured, it’s extremely useful to keep records of the configuration. This is especially important for the end user because a spare part might be required many years later. At this point in time, handwritten notes on the label might be difficult to read and the system integrator who did the original setup might no longer be available. Many programming tools on the market are unable to save and manage records of configuration data.

Traditional magnetic rotary encoders have had lower levels of precision and accuracy than high-quality optical encoders. However, newer encoder families combining Hall-effect sensing with optimized signal processing can rival the performance of optical encoders.

Incremental or absolute? Or both?
Traditionally, incremental and absolute encoders have been built around different design concepts. Moreover, features like resolution or multi-turn capability have been defined by different components such as code discs. The iXarC encoders are designed using a different approach.

All electronic components of a multi-turn encoder are integrated on a single 35-mm printed circuit board. No backup battery is required as this technology is capable of generating a sufficient amount of energy to record complete revolutions when the shaft of the encoder is turned. This energy generation does not depend on rotational speed. As a result, the encoder can be rotated for an indefinite number of times over long periods—with or without external power being available—without losing track of its absolute position. A powerful microcontroller and signal-processing platform within the encoder is used to create incremental output signals and calculate absolute position data that are transmitted on an SSi interface for absolute measurements and TTL or HTL interfaces for incremental readings. By changing the software configuration, this encoder platform can become a pure incremental encoder, a single-turn encoder, a multi-turn encoder or an encoder with SSi+ incremental output.

POSITAL’s programmable encoders are available in a large variety of mechanical configurations, including 36, 42 and 58 mm flanges and a variety of shaft types (solid shaft or blind hollow shaft versions with a range of shaft diameters). Additional adapters and flanges ensure compatibility with all common standards in America, Asia and Europe. Radially or axially positioned connectors and cable outputs are both available. Heavy-duty versions with an IP protection class of up to IP69K and up to 300 g shock resistance are available in both aluminum and 316L grade stainless-steel housings.

The measurement principle for magnetic encoders is based on an array of Hall-effect sensors that measure the orientation of the magnetic field created by a permanent magnet fastened to the encoder’s shaft. A microprocessor interprets the signals from the Hall-effect sensors and calculates the rotational angle.

Because a small number of devices can be programmed to take on a wide range of measurement tasks, distributors of incremental encoders can reduce their inventory levels by up to 80%. OEM customers using a variety of different incremental and SSi encoders can now cover different applications with a small number of devices, greatly simplifying supply chain and inventory management. System integrators can decide at the last minute how to tailor the encoder to specific requirements on site and initiate the purchase of the encoders while final design requirements are still under discussion. End users can receive spare parts from a distributor or system integrator quickly, reducing both downtime costs and shipping costs.

Reprint info >>

POSITAL-FRABA
www.posital.com

Linear motor stage with absolute encoder and ironless motor

July 31, 2015 By Mike Santora Leave a Comment

Physik Instrumente has released a new member of the PIMag family of precision positioning stages with magnetic direct drives. The compact ultra-precise V-551 motorized linear translation stage debuted at Laser World of Photonics, held in Munich, Germany last month.

V-551 comes equipped with an integrated absolute-measuring, 2nm resolution encoder – no more wasted time for referencing required. High velocity to 500mm/sec and quick acceleration is provided by a newly developed ironless magnetic linear motor, resulting in high accuracy and smooth motion. Precision crossed roller bearings with anti-creep cage assist guarantee excellent guiding accuracy (1 µm straightness / flatness per 100 mm).

Why Ironless Linear Motors?

Ironless non-cogging linear motors provide very smooth motion, and a high dynamic velocity range along with rapid acceleration. They are ideal for applications where high or extremely constant velocity is required, such as in optics inspection, metrology, photonics, interferometry, and semiconductor test equipment. The frictionless, zero-wear motor drives are also popular in fast automation applications, where reliability and maximum uptime are crucial. The V-551 is available with several travel ranges up to 230 mm.

Affordable Solution with Compact Controller, Custom Versions for OEMs

Together with PI’s compact C-891 controller, the V-551 stage forms a flexible and affordable positioning system. A lower cost stage variant that swaps the absolute encoder with a high-resolution incremental encoder is also available, as well as custom designs for OEMs with higher resolution, peak force, and different travel ranges.

Applications of V-551

Applications include industry and research, such as optics inspection, metrology, photonics, medical engineering and precision scanning in semiconductor or flat panel display manufacturing.

Physik Instrumente
www.pi-usa.us

Tiny kit-style encoder: New option for linear measurement

July 7, 2015 By Lisa Eitel Leave a Comment

A tiny linear encoder from RSF Elektronik is an MS 15 optical kit-style with the smallest mechanical profile in the industry. Available in North America through HEIDENHAIN, the encoder works in machinery for metrology, semiconductor, medical and automation.

The MS 15 optical kit-style encoder is 36 x 13.5 x 14.8mm in size, and provides a 40 μm grating pitch on an 8-mm wide steel tape carrier that has a double-stick backing for mounting directly to the machine axis. More after the jump.

The measuring tape comes with accuracies of ±5 or ±15 μm per meter and comes in lengths up to 20 m.

The tape lets the designer pick the reference mark, as the marks are printed every 50-mm and a sticker placed on the scale is used to highlight which reference mark is needed.

The tape also features the use of optical limits where separate stickers are placed on the scale that are detected by the reader head which sends the limit signals to the control or readout. A mounting tool is also offered to help install the measuring tape onto the machine axis with precision.

The MS 15 reader head has compensation built-in to continuously adjust signal deviations of amplitude, offset, and phase. This online compensation reduces interpolation error significantly.

The reader head also has a status LED which indicates to the user the mounting condition of the reader head with respect to the scale.

The reader head is available with 1-V peak to peak analog output, or a digital TTL output with a resolution down to 100 nanometers. Velocity of the reader head can be up to 10 meters per second.

Fagor Automation introduces Nanometer High Resolution Linear Encoders

January 27, 2014 By Jennifer Calhoon Leave a Comment

Fagor Automation Corporation has developed and introduced a new line of Linear Encoders capable of 50 nanometer resolution. Designed for high performance markets such as precision grinders and the EDM market. In addition, due to the ability of the new product capability of achieving nanometric measurements directly from the encoder without the need for electronic interpolation, the encoders are an excellent Metrology solution as well. The new Encoders provide improved position and speed control that results in a superior surface finish of the manufactured parts and considerably improved smoother Machine axes positioning for added machine life. In addition, these new nanometer encoders have proven to be an excellent solution for high speed linear motors by improving the motors performance in terms of positioning accuracy and repeatability and smoothness due to the acute encoder resolution.

The new line of linear encoders are available in the well proven G, S and SV series extrusion platforms. The G series is a full sized robust extrusion capable of withstanding even the harshest of environments. The S & SV series utilize a more compact extrusion allowing for proper fitment within applications with limited space.

It should be mentioned, the G and SV series Encoders incorporate the Patented TDMS® (Thermal Determined Mounting System) that allows for minimum error deflection regardless of the environment by controlling the expansion and contraction of the scale. The positioning errors originating from machine mechanics are minimized as the encoder is directly mounted to the machine surface and the guide ways. The encoder sends the real machine movement positional data to the CNC, therefore, mechanical errors due to thermal behavior, pitch error compensation and machine backlash are minimized.

Nanometer Resolution Encoders are available in travels up to 3 Meters and are subjected to an extensive final accuracy check. This control test is carried out on a computerized measuring machine equipped with a laser interferometer located inside a climate controlled chamber. The printed result of each individual test is supplied with every Fagor encoder. This allows Fagor Automation to guarantee accuracy on each and every Linear Encoder sold.

This new product offering expands an already broad spectrum of Fagor Encoder products which includes a large variety of Linear, Rotary & Angular encoders available in a selectable range of resolutions and accuracy as well as a multitude of protocols including Absolute and Incremental. In addition, Fagor Encoders are compatible with most CNC manufacturer’s protocols.

Fagor Automation is a world wide Manufacturer of CNC Systems, Servo Motors & Drives, Feedback Systems, DRO Systems & Motion Control Systems and can be reached with any inquiries at the below contact information.

Fagor
www.fagorautomation.com