Rotary 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

Large through-hole angle encoders from HEIDENHAIN offer high accuracy

November 6, 2018 By Miles Budimir Leave a Comment

HEIDENHAIN’s new sealed angle encoders can be used as an alternative to modular angular encoders in motion control machining applications that require a larger than usual through-hole. The new RCN 6000 series absolute sealed angle encoders with integral bearings have an exceptionally large hollow shaft diameter of 180 mm (7.09 in.), allowing larger scale machines to take advantage of high resolution and signal quality that’s expected from HEIDENHAIN angle encoders.

Common applications for the RCN 6000 encoders are large-scale rotary tables and radio telescopes which can easily adapt their design to the encoder while the integrated stator coupling ensures ideal alignment of the components involved in the scanning process, even if there are deviations in the shaft coupling.

Unlike other angle encoders with integral bearing, the RCN 6000 series encoders use HEIDENHAIN’s METALLUR process (in which the graduation is applied directly to the bearing ring) and a reflected light scanning method which gives it compact dimensions and larger mounting tolerances when compared to other products of its type. These integrated features along with the compact design keeps mounting difficulty to a minimum while making the most of its unique shape.

The RCN 6000 encoder provides a through hole of 180 mm, overall height of 44 mm, a system accuracy of ±2 in., can handle speeds up to 200 rpm, is able to interface with EnDat22, Fanuc05 and Mit03-4, and has an IP 64 protection reducing the effort required for protective measures.

For more information, visit www.heidenhain.us.

Posital upgrades family of analog programmable rotary encoders

October 19, 2018 By Paul Heney Leave a Comment

Encoder specialist Posital has announced a new generation of analog rotary encoders for position control. Compared to the company’s earlier analog encoders, these new models feature improved accuracy, faster dynamic response and new programming options. They also accept a wider range of supply voltages, an advantage for mobile machinery applications.

Posital’s analog encoders are designed for positioning tasks that use analog control systems. Outputs are either voltage (0-5 V, 0.5-4.5 V, 0-10 V or 0.5-9.5 V) or current (0-20 mA or 4-20 mA). The magnetic measurement mechanism is wear-free and extremely durable so that these devices offer much better accuracy, reliability and service life than conventional potentiometers.

An important feature of the analog encoders is that they are programmable with measurement characteristics that can be customized to meet specific application requirements, (This feature is also available with Posital’s digital encoders with SSI and incremental interfaces.) Programming can be carried out at the factory, in a distributor’s warehouse or at the customer’s job site, thanks to the company’s easy-to-use UBIFAST programming tool.

Programmable characteristics include direction of rotation (CW or CCW), zero set and the encoder output range. Measurement range programming allows the full range of electrical outputs (voltage or current) to be set to match a user-defined range of mechanical motion, resulting in significant improvements to control system accuracy.

For single-turn models, the measurement range can be set to 90°, 180°, 270° or 360°. For multi-turn models, the range can be set anywhere between 1 and 65,536 complete rotations. Analog encoders are available with push-buttons on the housing that enable the user to easily specify the upper and lower limits of the mechanical motion, with the electrical output fully spanning this range.

Posital
www.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.

Joral introduces true non-contact rotary encoder with rectangular design

April 2, 2018 By Paul Heney Leave a Comment

PE18 ProxEncoder non-contact rotary encoder product line receives a square housing with side sense capacity. Enhancing the original PE18 proximity style form factor, the new rectangular design allows for easy mounting on flat surfaces. Two USPTO patents enable the PE18-BX ProxEncoder to detect on-axis rotation with up to 0.5-in. (12mm) air gap between the application and sensor.

The PE18-BX is 100% encapsulated for an IP69k configuration that survives destructive conditions like submersion in hydraulic oil, deep sea salt water, dust control spray, or corrosive wash. The PE18 ProxEncoder product line is designed to cater to both mobile hydraulic and industrial installations. It is available in common communications including analog, quadrature, and CAN J1939.

Highlights of the Joral PE18 ProxEncoder include:

Face or side oriented sensor target area
Patented true non-contact position sensing:
- 5-in. (12mm) gap between sensor and application
- 10-in (2.5mm) axial misalignment
- 30° planar tilt
IP69k environmental protection class
Rated MIL-STD 202 for shock and vibration resistance
Available Outputs: Quadrature, CAN J1939, PWM, Analog, and more
Customizable connector options available

Joral
www.ProxEncoder.com

POSITAL expands rotary encoder offerings with new through-hollow incremental encoders

March 22, 2018 By Miles Budimir Leave a Comment

POSITAL has extended is portfolio of rotary encoders with a new family of through-hollow incremental encoders. These devices are designed to be installed with the machine shaft passing through the sensor. They can be used to monitor rotary motion in a wide variety of machinery, including servomotors, material handling equipment and printing presses, offering cost-effective, space-saving solutions. For motors, they can be easily installed between the body of the motor and other components mounted on the shaft.

POSITAL’s through-hollow encoders are available for shaft diameters ranging from 3/8 in. (9.5 mm) to 1-3/4 in. (44.5 mm). The smaller units (up to 14 mm shaft opening) have an external diameter of 2-1/4 in. (58 mm), while the larger units (5/8 in. to 1-3/4 in. shaft size) have external diameters of 3 or 4 in. (77 or 100 mm). Available resolutions for these devices extend from 360 PPR to 4,096 PPR (pulses per revolution.)

All through-hollow encoders have rugged aluminum housings and environmental protection rated at IP65, ensuring longevity and high levels of operational safety. All variants are available with a variety of communications interfaces, including RS422 (TTL) 5 V or 11-30 V and Push-Pull (HTL, 5-30 V). Connection options include built-in cables or MIL-type connectors.

POSITAL’s through-hollow encoders are a good option for machine builders and system integrators who are looking for accurate motion feedback devices that are easy to build into new or existing designs.

For more information, visit www.posital.com.

True non-contact rotary encoder

March 2, 2018 By Mike Santora Leave a Comment

Joral LLC introduces the PE18 ProxEncoder non-contact rotary encoder product line. Modeled in a threaded proximity switch housing, the 18mm true non-contact encoder is designed to capture rotary motion where conventional sensors fail. Two USPTO patents enable the PE18 ProxEncoder to detect on-axis rotation with up to 0.5-in. (12mm) air gap between the application and sensor.

The PE18 is 100% encapsulated for an IP69k configuration that survives destructive conditions like submersion in hydraulic oil, deep sea salt water, dust control spray, or corrosive wash. Immediately available in common communications including analog, quadrature, and CAN J1939. The PE18 ProxEncoder product line is designed to cater to both mobile hydraulic and industrial installations.

Additional highlights of the Joral PE18 ProxEncoder include:
18mm threaded proximity switch style housing
Patented true non-contact position sensing:
o 0.5-in. (12mm) gap between sensor and application
o 0.10-in. (2.5mm) axial misalignment
o 30° planar tilt
IP69k environmental protection class
Rated MIL-STD 202 for shock and vibration resistance
Available Housings: Anodized aluminum and stainless steel
Available Outputs: Quadrature, CAN J1939, PWM, Analog, and more
Customizable connector options available

Joral
www.joralllc.com

Joral debuts non-contact rotary encoder for harsh environments

March 1, 2018 By Miles Budimir Leave a Comment

Joral LLC introduces the PE18 ProxEncoder non-contact rotary encoder product line. Modeled in a threaded proximity switch housing, the 18-mm true non-contact encoder is designed to capture rotary motion where conventional sensors fail. Two USPTO patents enable the PE18 ProxEncoder to detect on-axis rotation with up to 0.5-in. (12 mm) air gap between the application and sensor.

The PE18 is 100% encapsulated for an IP69K configuration that survives destructive conditions like submersion in hydraulic oil, deep sea salt water, dust control spray, or corrosive wash. It is available with common communications including analog, quadrature, and CAN J1939. The PE18 ProxEncoder product line is designed to cater to both mobile hydraulic and industrial installations.

Additional features of the PE18 ProxEncoder include:

18-mm threaded proximity switch style housing
0.10-in. (2.5-mm) axial misalignment
30° planar tilt
Rated MIL-STD 202 for shock and vibration resistance
Available Housings: Anodized aluminum and stainless steel
Customizable connector options available

To learn more about the PE18 ProxEncoder and see a working animation, visit www.ProxEncoder.com.

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.