Absolute Encoders - Motion Control Tips

Encoder Products absolute encoders – now with improved electronics

April 2, 2019 By Danielle Collins Leave a Comment

EPC’s line of absolute encoders offers magnetic multi-turn technology and higher resolution.

Encoder Products Company (EPC) offers a full line of absolute encoders with models in both shaft and blind hollow bore, in sizes 36 mm, 58 mm, and standard size 25 with a 2.5 inch housing. Now, EPC absolute encoders come with even more communication options and higher resolution.

Absolute Technology

An absolute encoder is a device that provides a unique code for each increment of shaft rotation, meaning that an absolute encoder indicates both that the shaft position has changed, and the absolute position of the shaft. EPC’s absolute encoders now offer a higher resolution of 16 bits for single turn resolution and 43 bits for multi-turn resolution, allowing these absolute encoders to measure smaller increments, and allowing a longer run-time before reset.

“Absolute encoders are becoming more and more prevalent in industry,” explains Sarah Walter, EPC Technical Applications Engineer. “They offer connectivity, are more resistant to electrical noise, and retain position information after a power loss.”

Absolute encoders are ideal for safe operation of systems that always need exact location information to prevent damage to equipment or bodily injury. This is especially true in the event of a loss-of-power scenario. EPC absolute encoders maintain position value without being powered, so if there is rotation during the power loss, this movement is tracked and retained. Once power is restored, the encoder can transmit the location information immediately.

As more equipment and industries rely on real-time data, absolute encoders make an excellent motion feedback solution. There is no longer a need to use additional devices and time to calculate positional data. EPC’s absolute encoders offer real-time information with SSI, CANopen, and EtherCAT communication protocols. Watch the video for more information.

EPC Absolute Encoders offer:

16 bit resolution for single turn, and 43 bit resolution for multi-turn
SSI, CANopen or EtherCAT communications
Maintenance-free and environmentally-friendly magnetic design
Energy harvesting magnetic multi-turn technology
No gears or batteries
Electronic cam switches on CANopen and EtherCAT models
Compact design with bus cover

Encoder Products Company

What features make resolvers suitable for harsh environments?

March 29, 2019 By Danielle Collins Leave a Comment

Resolvers were initially developed for military applications and are probably best known as the preferred feedback solution in harsh environments. Where optical or magnetic encoders are sensitive to dust, liquids, and magnetic fields, resolvers can operate in dirty, humid, wet, and high-radiation environments. But what is it that makes them so robust under conditions that would damage or interfere with other feedback devices? The key is separation of the electronics from the resolver itself.

A resolver is essentially a rotating transformer, consisting of a rotor with one primary winding and a stator with two secondary windings. The two secondary windings are oriented 90 degrees from each other and are referred to as the sine and cosine windings. The rotor is attached to the rotating part that is being measured — such as a motor shaft — and the stator is stationary.

An AC voltage with constant frequency (in the range of 2 kHz to 10 kHz) excites the primary winding, which induces voltage in the two secondary (sine and cosine) windings. The induced voltages will have the same frequency as the supply, or reference, voltage, but because the two secondary windings are 90 degrees out of phase, the induced voltages in the secondaries will also be 90 degrees out of phase.

The voltages induced in the sine and cosine windings are directly related to the shaft angle (θ)
Image credit: Advanced Micro Controls, Inc.

The amplitudes of the induced voltages are proportional to the angular position of the shaft. Therefore, the shaft angle can be determined by taking the arctangent of the ratio of the sine voltage to the cosine voltage (sinθ/cosθ = tanθ). And because shaft position is determined only by the voltage ratio of the secondary windings, the position information is absolute, meaning the resolver can always determine the shaft position — even if it has been powered down and restarted — without having to move to a reference or index signal.

The induced voltages (sine and cosine) are 90 degrees out of phase.
Image credit: Teledyne LeCroy

Note that no mechanical components, optics, or sensors are required for a resolver to work. This is the key to the resolver’s ruggedness. The electronics that convert the resolver’s analog output to a digital signal (sometimes referred to as an R/D converter) that the controller can accept are housed separately from the resolver itself. This means that contamination, vibration, extreme temperatures, and even radiation have little or no effect on the resolver’s operation.

In this steel mill application, a resolver is connected to a lead screw (middle) that positions side guides during the rolling process.
Image credit: Dynapar

Resolvers are often used for commutation and speed control of motors.
Image credit: Nidec-Avtron

In theory, resolvers have infinite resolution, since every rotational position of the shaft is associated with a unique sine/cosine voltage. But signal conditioning — the R/D converter — limits both accuracy (typically in the range of 3-15 arcminutes) and rotational speed (typically 5000 rpm or less).

One way to achieve higher accuracy is to use a multi-speed resolver. In this design, the number of magnetic poles is increased, so each mechanical revolution creates multiple sine and cosine curves. The downside of multi-turn designs is that they lose the ability to provide absolute feedback. But there is a way to get absolute feedback and better accuracy from resolver set-ups — by mounting, or “stacking,” a single-speed resolver on top of a multi-speed resolver.

Feature image credit: Dynapar

POSITAL adds to its range of kit encoders

December 5, 2018 By Lisa Eitel Leave a Comment

POSITAL is expanding its line of kit encoder solutions for motion control applications to satisfy a wider range of needs faced by machine builders, system integrators, and motor manufacturers.

Kit encoders are component-level products, designed to be built into motors or other types of equipment where real-time measurement of rotary position (angular displacement) or rotational speed is required. Compared to POSITAL’s widely used IXARC series of self-contained encoders, kit encoders typically lack sealed housings, ball bearings or separate shafts. Instead, they are intended to fit inside the host machine’s casing, with rotating components connected directly to the machine’s shaft. This results in rugged, compact installations with direct measurement of rotational position and speed.

The POSITAL kit encoder family now includes:

Multi-turn battery-free magnetic kit encoders: These provide absolute position feedback in a compact, rugged, low-maintenance package. Multi-turn models feature a rotation counter that is self-powered, eliminating the need for backup batteries. This makes these units highly reliable and virtually maintenance-free. Variants for stepper motors that feature the same mounting footprint as popular incremental encoders are available, providing motor builders with a convenient upgrade path to absolute position control. POSITAL’s magnetic kit encoders support non-proprietary communications interfaces, including SSI, BiSS C and BiSS Line.

Through hollow kit encoders are designed for installations where there are benefits to having the measurement element fit around a machine’s shaft or axle. With their slim design (only 18 mm thick) and generous central opening (30 or 50 mm) these are an excellent solution for many motor installations and compact robot joints. These devices are based on a capacitive measurement technology that combines accuracy with tolerance to shock and vibration, dust and moisture, and magnetic fields. Here again, battery-free multi-turn models are available.

Compact incremental optical kit encoders are optimized for speed control of small drives, low power motors and stepper motors. These devices are simple, robust and easy to install, with a mounting footprint that is compatible with optical kit encoders from other manufacturers. They are available with a wide range of resolutions.

Magnetic Kit encoders are currently available. For more information, visit www.posital.com.

What is an LVDT (linear variable differential transformer)?

November 3, 2018 By Danielle Collins Leave a Comment

A linear variable differential transformer (LVDT) is an absolute measuring device that converts linear displacement into an electrical signal through the principle of mutual induction. Its design and operation are relatively simple, providing extremely high resolution in a device suitable for a wide range of applications and environments.

The main components of an LVDT are a transformer and a core. The transformer consists of three coils — a primary and two secondaries (S1 and S2) — wound on a hollow form, which is typically made of glass-reinforced polymer. The coils are arranged such that the primary coil is located between the two secondary coils, which are symmetrical and wound in series but in opposite directions (referred to as series-opposed winding).

The core is made of magnetically permeable material and moves freely inside the bore of the transformer. A non-ferromagnetic shaft, or push rod, is coupled to the core and connects to the object being measured.

Image credit: Honeywell International

When voltage is applied to the primary winding, the resulting flux is coupled to the secondary windings by the core. This induces voltages (often denoted E1 and E2) in each of the secondary windings. The differential voltage in the secondary windings determines the distance moved, and the phase of the voltage indicates the direction of movement.

Here’s how it works…

The series-opposed winding of the secondary coils means that when the core is at the center of the transformer (equidistant between the two secondary coils), the induced voltages have equal amplitude but are out of phase by 180 degrees. Thus, the induced voltages cancel each other, and the output voltage is zero. (This is often referred to as the null point.)

When the core moves to one side — toward S1 for example — the secondary coil on that side becomes more strongly coupled to the core, causing the induced voltage (E1) of that secondary to be higher than the induced voltage (E2) of the opposite secondary (S2). The differential voltage output (E1 – E2) determines the amount of movement.

The amplitude of the differential output voltage determines the distance traveled, and the phase of the output voltage indicates the direction traveled.
Image credit: TE Connectivity

The induced voltage (E1) of the first secondary coil is in-phase with the primary voltage, indicating the direction of movement. Conversely, when the core moves to the other side of the transformer, the induced voltage (E2) of that secondary coil is out of phase with the primary voltage, indicating movement in the opposite direction.

The output of an LVDT is a direct and linear function of the input across its specified measuring range, although linearity falls off as the core reaches or exceeds the ends of its range. However, it is possible to use an LVDT beyond its specified range, in some cases, with a pre-defined table or polynomial function to compensate for the nonlinearity.

LVDT output is a direct, linear function of the input voltage up to the device’s specified measuring range. Beyond this point, linearity begins to fall off.
Image credit: TE Connectivity

An LVDT contains no electronics, but external electronics — referred to as a signal conditioner — include an oscillator to generate the drive signal, along with a demodulator, an amplifier, and a low-pass filter to convert the AC output voltage to a DC signal. Because they rely on the coupling of magnetic flux, LVDTs have almost infinite resolution, limited only by the noise in the signal conditioner. Similarly, repeatability is extremely high — typically less than 0.1 percent of the measurement range. Common measurement ranges are from ± 0.25 mm to ± 750 mm.

Signal conditioning electronics can be contained inside the LVDT housing. This configuration is typically referred to as a DC LVDT because the primary coil is supplied with DC voltage. Although internally-housed electronics reduce complexity, DC LVDTs have lower resistance to shocks, vibrations, and temperature extremes than traditional AC LVDTs.

LVDT devices are extremely robust, since there is no physical contact, and therefore no friction or wear, between the moving core and the transformer bore. The transformer is typically encapsulated with epoxy to protect against contamination and moisture, and the housing can be made from a wide variety of materials — from stainless steel to nickel alloys or titanium.

Typical applications include tensile test and other material testing devices, load cells, and weighing devices. LVDTs are also used to measure displacement in hydraulic cylinders and actuators.

Heavy-duty absolute encoders — now with EtherCAT communications

October 2, 2018 By Lisa Eitel Leave a Comment

New EPC Model A58HE and Model A58SE are EtherCAT-ready, multi-turn absolute encoders for harsh factory and plant environments. They work in applications where fieldbus connectivity is required, and the encoder must retain absolute position information after power-off events. The Model A58HE is a 58-mm encoder in a hollow-bore construction, and the Model A58SE is a 58-mm shaft encoder available with either a clamping flange or synchro flange.

EPC’s Models A58HE and A58SE offer EtherCAT Deterministic Communication: CoE, FoE, EoE

“Both the A58HE and A58SE encoders are easily designed into a wide variety of applications,” says Sarah Walter, electrical engineer and EPC Technical Sales Manager.

“They plug directly into a network with minimal prerequisites, and work in various configurations, including daisy-chaining, and redundant-ring configurations that can continue communication in event of a line break. That makes for quick installation and facilitates data exchange among connected devices, allowing companies to transition to a networked system and facility … and these encoders work with CANopen over EtherCAT, so for users familiar with CANopen technology, implementation will be straightforward.”

The Model A58HE and Model A58SE Absolute Encoders offer:

EtherCAT Deterministic Communication
Multi-turn resolution up to 43 bits
Up to 16 bits of single turn resolution
58-mm-diameter housing; bores sizes up to 0.375 in. or 15 mm
Shaft diameters up to 0.375 in. or 10 mm; durable magnetic technology
Proven turns counting technology with no gears or batteries
Operating temperature range of -40° C to 85° C
Sealing rating of IP65 (on A58SE, 10 mm shaft comes with IP67 sealing)
Continuous digital position monitoring; ability to retain absolute position after a power outage
Meet CE/EMC standards for immunity and emissions

Encoder Products Company (EPC) is a leading designer and world-wide manufacturer of motion sensing devices. EPC began operations in 1969, producing a line of custom encoders from a small, home-based shop. Today, EPC is the largest privately-held encoder manufacturer in North America, producing a complete line of incremental and absolute rotary encoders and accessories in a 100,000 ft² vertically integrated facility in Idaho. For more information, visit encoder.com.

POSITAL closed-loop motor feedback for absolute positioning

July 2, 2018 By Lisa Eitel Leave a Comment

POSITAL FRABA encoders for closed-loop motor feedback allow upgrades to existing motion control applications. The mechanical drop-in replacement encoders have the same footprints as US Digital’s E5 models and Broadcom’s (Avago) HEDS-5500 models.

POSITAL kit encoders provide absolute position feedback — to give controls complete information on the physical position of the mechanical components they’re directing.

Many motion designs are designed around incremental encoders because incremental feedback devices were once less expensive than absolute encoders. But now POSITAL’s absolute kit encoders are comparable to those of incremental encoders, so design engineers must no longer make the choice based on cost.

• Identical assembly procedure to that of comparable encoders; no training required; diameters 4 to 10 mm (1/4 to 3/8 in.)

• Magnetic technology (to withstand harsher environments than optical encoders); improved connectivity via m12 connector additional available

Multiturn Absolute Kit Encoders from POSITAL are based on magnetic sensing technology. More specifically, the multiturn counting system is powered by Wiegand wire energy harvesting technology, which enables the absolute encoder to maintain true absolute position over power cycles and rotation of the encoder during power off conditions.

With 17 bits (131072 positions) of single turn resolution and 16 bits (65536 turns) of multiturn range, KCD Absolute kit encoders from POSITAL are ideal for position control applications.

For more information, visit this deep link to the absolute-encoder page at posital.com.

Totally encapsulated J1 rotary encoders IP69k electrical protection from Joral

May 9, 2018 By Lisa Eitel Leave a Comment

Joral LLC now has a new method to impart total encapsulation in its J1 electronic components. Specially crafted to ensure total protection from extreme temperature fluctuation, intense machine vibration, and pressure wash down, the Joral J1 line-shafted rotary encoders perform rotary motion feedback for industry, ranging from directional drilling rigs to timber harvesters.

Shafted J140 with shell removed displaying total encapsulation

Totally encapsulated J1 rotary encoders IP69k electrical protection from Joral

The new IP69k electrical protection and encapsulation process now available for J1 line shafted rotary encoders is comperable to that of the newly released ProxEncoder noncontact rotary encoder. The Joral encoders in the J1 Line come in J1939, voltage, and quadrature outputs, and other versions.

Prototyped on a FDM 3D printer, the new encapsulation method creates a fully protected electronics package, which creates an environmental barrier between the J1 Line Encoder’s shaft and bearing package. The new IP69k encapsulation is available immediately as a standard production item. Visit www.JoralLLC.com for more information on totally encapsulated J1 rotary encoders — as well as customizable connections and various output options.

Connection options include terminal, block, M12, M12 Pigtail, flying lead cable, M8, and Deutsch connectors.

Features of the totally encapsulated J1 rotary encoders

Totally encapsulated electronics (IP69k); shaft seal available for IP68 housing protection (IP67 standard)
Absolute multi-turn capable and rated MIL-STD 202 for shock and vibration
From the manufacturer of the PE18 ProxEncoder
Available outputs include quadrature, CAN J1939, PWM, analog, and more
Customizable connector options available

Founded in 2005, Joral LLC is the culmination of a long history of development in encoder and sensor technology by companies including Joral Devices, Joral Computer Services, and GS Global Resources. Today, Joral develops and manufactures harsh-duty electronic devices for mobile hydraulics and industrial applications. Joral has redefined the “rugged duty” position sensor by introducing protection methods such as total electronic package encapsulation, LED status indicators, and patented true non-contact coupling. For more information, visit www.joralllc.com or email sales@joralllc.com.

POSITAL Motor Feedback Kit Encoders — now with open-source BiSS interface

January 25, 2018 By Lisa Eitel Leave a Comment

Rotary encoder specialist POSITAL has expanded its interface offerings for its magnetic Kit Encoders with support for the nonproprietary open-source BiSS Line communication protocol. This enables the practical implementation of single-cable technology, which is becoming increasingly popular with motor and robot manufacturers. POSITAL’s easy-to-install motor feedback kits, which feature 17-bit electronic resolution, bridge the gap between simple resolvers and more complex and expensive optical encoders for servomotors, robot joints and other applications where absolute rotary position feedback is required.

POSITAL’s magnetic Kit Encoders support open-source BiSS Line communication protocol, enabling Single-Cable technology.

Single-cable technology involves the transmission of power and encoder signal in a single cable. The one-cable approach offers significant benefits for smaller motors where the placement of two connectors has always been awkward because of the lack of space. What’s more, reduced cabling reduces costs, while reducing the number of connectors reduces susceptibility to connector failures. A special feature of the BiSS Line interface is the implementation of the Forward Error Correction function (FEC), which improves availability of data communications, even with faulty cables and plug connections.

“All in all, BiSS Line is a suitable interface for servomotors … and not just for cost reasons, but also for optimized performance,” says Christian Fell, POSITAL’s V.P. of Technology and General Manger for the Americas. A four-wire setup (with separate conductors for communication and power supply) or a two-wire variant (with combined communication and instrument power supply on a wire pair), are also available, based on the same communications protocols.

From their original introduction, the new motor feedback kits were available with vendor-neutral digital communication interfaces such as BiSS-C or SSI for absolute measurements. “A number of optical feedback systems on the market make use of proprietary interfaces such as Hiperface or Endat, which means an ongoing dependency on the encoder manufacturer. We deliberately took a different approach,” emphasizes Fell. “We are whole-hearted advocates of open-source interfaces – and stick to them consistently.” POSITAL’s commitment to the open-source strategy is affirmed by the fact that the encoder manufacturer is a founding member of the BiSS Association e.V. This new user organization (founded at the end of September) will promote the distribution of the free-of-charge BiSS family of open-source communication protocols worldwide.

POSITAL is a supplier of advanced industrial position sensors used in a wide variety of motion control and safety systems. The company is also an innovator in product design and manufacturing processes and a pioneer of Industry 4.0 (Industrial Internet of Things/IIoT), offering customers the benefits of built-to-order products combined with the price advantages of mass-production. POSITAL is a member of the Intl. FRABA group, whose history dates back to 1918, when its predecessor, Franz Baumgartner elektrische Apparate GmbH, was established in Cologne, Germany to manufacture relays. Since then, the company has played a trendsetting role in the development of rotary encoders, inclinometers and other sensor products. POSITAL has a global reach with subsidiaries in Europe, North America and Asia – and sales and distribution partners around the world.

What is modulo positioning?

January 12, 2018 By Danielle Collins Leave a Comment

Cutaway of a multi-turn encoder.
Image credit: A-Tech Instruments Ltd.

In motion control, there are typically two types of positioning that can be used for a linear or rotary axis: relative, in which each position is based on a previous position, regardless of the actual position of the axis; or absolute, in which each position is referenced to a home, or zero, point.

Axes that have very long strokes, or those with “endless” positioning, such as rotary tables and conveyors, typically use multi-turn absolute encoders. Multi-turn designs can track the encoder’s position over many revolutions – typically up to 4096. (This is in contrast to single-turn encoders, which reset the position value after each full encoder revolution.) But even absolute positioning using a multi-turn encoder leaves the axis at risk of significant positioning error if the application exceeds the maximum number of encoder revolutions.

In mathematics, the modulo operation finds the remainder after the division of two numbers. A simple example: (9 mod 4) equates to 1, because when 9 is divided by 4, the remainder is 1.

This is where modulo positioning comes in. Take for example, a rotary table with a 16-bit multi-turn absolute encoder (capable of 2¹⁶, or 4096 turns) mounted to the motor, and driven through a 5:1 gear ratio. In this configuration, every 1 turn of the table requires 5 turns of the motor and encoder. Once the encoder exceeds 4096 turns, an overflow occurs, and the encoder starts counting from zero again.

When a multi-turn encoder exceeds its maximum number of revolutions, modulo positioning stores the overflow and ensures that no position information is lost.
Image credit: Lenze Automation GmbH

The first move requires 4.8 table revolutions (4 revolutions + 288 degrees), meaning the motor and encoder have made 24 revolutions (4.8 * 5 = 24). The encoder stores this information, and when the system is powered off and back on, it recognizes the position correctly.

The next move is much larger, with 825.6 table revolutions (825 revolutions + 216 degrees), meaning the motor and encoder make 4128 revolutions (825.6 * 5 = 4128). Because the encoder has exceeded its maximum of 4096 revolutions, an overflow occurs, and the encoder starts counting from zero again, recording only 32 motor/encoder revolutions (4128 – 4096).

When the system is switched off and then on again, it only recognizes that 32 motor/encoder revolutions, or 6.4 table revolutions (6 revolutions + 144 degrees), have taken place. The additional 72 degrees of table movement (216 – 144 = 72), which equals one full motor revolution (72 * 5 = 360), is missing. This loss of position happens each time the encoder exceeds its 4096 revolution limit.

Note that the overflow problem does not occur if the maximum number of encoder turns can be evenly divided by the gear ratio. For example, a gear ratio of 8:1, when used with a multi-turn encoder that has a maximum of 4096 turns, does not cause lost position, because 8 divides into 4096 evenly (4096 ÷ 8 = 512).

With modulo positioning, the overflow occurrence is stored in the controller, preventing the loss of positioning information. Alternatively, if the drive offers a “modulo” function, it can be enabled to track and store any encoder overflows. The modulo function is straight-forward to use, requiring the user to enter the modulo value (typically 360 degrees), the relationship between motor/encoder turns and axis turns (or linear travel), and the encoder type and resolution. Both modulo positioning solutions – controller-based or drive-based – ensure that the overflow is accounted for and the actual position is corrected accordingly.

Absolute, high-resolution motor feedback sensor from SIKO

August 2, 2017 By Miles Budimir Leave a Comment

The MSAC501 absolute sensor from SIKO offers a truly absolute solution for measuring motor feedback. The exact sensor position is available immediately after a current interruption so additional reference or mechanical activity is not necessary.

The MSAC501 sensor works with standardized SSI or RS485 interfaces. An optional LD output for digital signal output is also available. Rim speeds of 25 m/sec (incremental) or 5 m/sec (absolute) can be easily realized. The MSAC501 has a system accuracy of up to +/- 0.06 ° (in combination with the magnetic ring MRAC501); resolution and repeatability can even reach +/- 0.0014 °.

All components are rated at protection class IP67 and can be used across a broad range of temperatures, from -30 to + 80° C. The sensor has a high contamination tolerance (dust, oil, grease), long working life, and resistance to wear thanks to the contactless, magnetic measuring principle.

As a “partner” for the MSAC501 sensor, the MRAC501 (solid aluminum ring) and the MBAC501 magnetic tape are available. The MRAC501 is available as a solid ring with fixed aluminum flange, and is therefore suitable for measuring revolutions up to 360 ° (single turn). The MBAC501 measuring tape includes a magnetic tape and steel carrying case, and is designed for self-assembly by the customer on a ring or external radius. With this combination, measurements can be conducted over a range of 360°.

These different components can serve a large variety of requirements, regardless of whether they involve different diameters of bottles, different interfaces, special resolutions, high accuracy demands, or simply extreme robustness with respect to dust and dirt.

The MSAC501 sensor is already available on the market and can be tested free of charge on request by contacting SIKO GmbH.

For more information, visit www.siko-global.com/p/msac501.