Shock tolerant heavy-duty encoder insulated to 2.5 kV

This edited  article come from encoder manufacturer Leine & Linde

It’s sometimes the small modules such as rotary encoders in production equipment that make it necessary to shutdown a plant for their replacement in case of faults. This results in enormous costs, often way out of proportion to their size. In the windpower industry, revenue loss from downtime can average $50,000/week, part replacement can vary from $20,000 to $300,000, and if a crane must be mobilized, expect a $250,000 charge.

Such charges can be avoided by using rotary encoders capable of self diagnosis that indicates internal problems so maintenance can be planned as early as possible.

Rotary encoders are key components of modern machinery and plant controls, so it makes sense to equip them with a diagnostic system that continuously monitors the internal functions of the rotary encoder and provide a basis for initiating maintenance measures in good time. Rotary encoders used in production plants are often subjected to high stresses from shock and vibrations as well as high temperatures. The following typical component specifications reflect these stresses: Vibration-resistance up to 100 m/s², shock resistance up to 1,000 m/s², axial load 100N and radial loads to 300N. Under these general conditions a positioning accuracy of 0.1 mm must still be ensured.

 

Why rotary encoders fail

It is no wonder that rotary encoders break down in spite of their apparent durability. Encoders can fail for several reasons. For instance:

• Worn-out ball bearings due to poor installation: The connection of the rotary encoder to the motor shaft is made either with a coupling (typical for shaft encoders) or by plugging onto the shaft (typical for hollow shaft encoders). A torque support keeps the encoder from spinning. If the specified tolerances are not complied with, imbalance results, which causes premature wear to the ball bearings. The result: the increment-disc wobbles. Individual areas lose contrast, which in turn looses several pulses. This means the rotary encoder still functions, but the entire drive unit becomes irregular as the frequency inverter attempts to compensate for these fluctuations.
• A “loose contact” produces an imbalanced drive unit which puts excess strain on soldered joints and (terminal) contacts. Hence, bad contacting causes sporadic faults.
• Dirt in the rotary encoder clinging to the increment disc: The encoder then detects two increment lines as one and produces one pulse too few. This can happen with equipment in dusty regions common for windpower equipment, and especially when the nacelle cover is opened. In such cases it is advisable to use encoder versions with external plug connections.

• Moisture in the connector or in the housing: Cables too thin let moisture penetrate into the rotary encoder through the cable gland and cause sporadic malfunctions. This is especially possible in offshore windpower applications.

• Overheating: Rotary encoders are often installed behind a fan so the exhaust air from the motor passes over the encoder. If a motor runs hot, as it could as bearing fails, the hot exhaust air from the motor can cause the failure of the rotary encoder.
  

  Software for the ADS provides users with an overview of the type of rotary encoder problem, the time of the fault and the condition and encoder data.

A fault with many installations is also the fact that monitoring the rotary encoder is only implemented in the frequency inverter. However, between the inverter and rotary encoder there are enough cables and terminals to cause problems. For example, a crushed cable can lead to a signal interruption, which is mistakenly interpreted as an encoder fault by the inverter. Then an O&M crew would swap out a component without fixing the problem. A lot of these problems can be avoided if the encoder could tell why it is malfunctioning.

One such encoder from the author’s company has a built in early warning system called Advanced Diagnostic System (ADS). This automatic self-diagnosis works like this:

 

The rotary encoder internally monitors the completeness of the pulses and the correct pulse sequence. Even a single counter difference from the programmed division is registered by the system and reported via a potential-free switching output. This can, for example, be evaluated and displayed by an overriding system control system. For this an additional wire is necessary. In parallel to the switching output, the fault is indicated by a flashing LED on the rear of the housing. In case of upgrading, this allows using ADS without additional wiring. Often, rotary encoders are installed in visible position, so a sporadic visual check by the user is sufficient. The flashing LED can be easily seen at a distance of 10 m.

As part of ADS, the manufacturer stores the time of the fault and the corresponding error code in the rotary encoder so users have the opportunity to read out and analyze the error code via an RS-232 interface (once the encoder has been removed). For statistical purposes, the number of operating hours, speed of rotation and current temperature are also measured in the encoder. The highest and lowest temperature is also stored. In addition, there is a differentiation between individually occurring errors and continuous problems.

Leine & Linde
Leinelinde.com

The Sweden-based encoder manufacturer distributes in the U.S. through HEIDENHAIN Corp., Schaumburg, Illinois.

Heidenhain
heidenhain.com

No-drift absolute gaging package

The Acanto Absolute Length Gage with EnDat 2.2 has the benefits of an optical encoder and solves many of the problems of different length gages. Quality managers will not have to worry about gages drifting, linearity over the entire measuring range, or referencing upon startup. The device does not drift over time nor does it require mastering. “Sweet spots” are nonexistent because 2 µm accuracy is held throughout the entire measuring length. Controls let the unit know its position on power up without need for reference. The device comes in spring or pneumatically operated models and is offered in 12 mm and 30-mm measuring lengths.

In addition, the ND 2100G Gage-Chek handles gaging and inspection tasks with ease, from simple pass/fail detection up to complex logic statements to and from a PLC. They can be configured for basic or advanced operations where inputs can be assigned and combined as needed, along with mathematical, trigonometric or statistical formulas, making it possible to measure even complex dimensions such as thickness, flatness, volume, and more. Rapid acquisition of measured data can monitor dynamic events such as the eccentricity of a rotating shaft.

The unit can manage up to 100 parts, each with up to 16 visible measurement features and 16 hidden ones and can save thousands of data entry points for internal statistical process control or export. User customization is easy with programmable soft and hot keys. Min/Max functions monitor and store data, and warning and tolerance limits can be set to each display value.

A new plug-and-play routine allows easily interfacing the Acanto and ND 2100G GAGE-CHEK. The ND 2100G can interface with 1 to 8 Acanto Gages and will be an effective solution for many gaging applications. The ND 2100G Gage-Chek also accepts EnDat 2.2 encoders from Heigenhainincluding linear, rotary, and angle.

HEIDENHAIN CORP
http://www.windpowerengineering.com/directory/?s=Heidenhain&searchsubmit=Search

Absolute encoder well suited for electric motors

Recent absolute, inductive rotary encoder. Called the ECI 119, this encoder sets itself apart with a low profile (height of 19 mm, outside diameter 92 mm) and large through shaft (50, 38, or 30 mm), making it well suited for electric motors in many applications.

The Heidenhain ECI 119 is a single turn, absolute encoder offering 524,288 (19 bit) positions per revolution, and provides ±90 sec system accuracy. An advantage of the ECI 119 is its bearingless design. As a modular encoder, there is no need to worry about bearing wear or loading, and concerns of mechanical self heating of the encoder and shaft currents are eliminated. If all the mounting tolerances are met, the encoder requires virtually no maintenance outside of contamination protection.

The company’s two types of output are offered: purely serial data (EnDat21) or serial data with 1 Vpp incremental signals (EnDat 01). The SSI interface can also be implemented, but this requires a minimum value order. The EnDat feature lets users transfer incremental and absolute position data along with online diagnostics.

A recent version of Adjusting and Testing Software is available with the ECI 119. The software allows diagnostic checks of the encoder position signals. And the ExI Mounting Wizard allows checking the scanning gap and signal amplitude to assess mounting quality. This ensures reliable and repeatable field mounting.

Heidenhain Corp.
www.heidenhain.us

Low-profile encoders good for small motors

Low profile incremental rotary encoders with block commutation tracks are especially suitable for use in small-dimensioned servo motors. These rotary encoders of the Heidenhain 1000 and 1100 series come equipped with an industry-standard 35-mm diameter housing.

The encoders distinguish themselves by a short overall length and modern opto-ASIC based photoelectric scanning with integrated interpolation. Thanks to the electrical output at TTL levels with differential signals, the encoders can be connected to most all standard subsequent electronics for control of digitally controlled servo motors (up to edge lengths of 40 and 55 mm).

Currently available, the 1023 encoder has an overall length of 35.2 mm max and an IP 64 rating, making it useful in hazardous environments. The 1123 encoder has an overall length of 30.3 mm max and an IP 0 for general use.

Both encoders have mounted stator couplings and blind hollow shafts. Choice of appropriate commutation signals is available because the amount depends upon the number of poles of the motor to be controlled.

Heidenhain Corp.
www.heidenhain.us

Precise position measurements

EIB 741 is an external interface box for precise position measurements. This network-capable measuring device removes the requirement of a PC interface card usually necessary when connecting measurement apparatus to an industrial PC or laptop.

The EIB 741 works well at inspection stations and multipoint inspection apparatuses as well as for mobile data acquisition, such as in machine inspection and calibration. A maximum of four Heidenhain encoders, either with sinusoidal incremental signals (1 Vpp) or with EnDat interfaces (EnDat 2.1 and EnDat 2.1), can be connected to the EIB 741.

This external interface box subdivides periods of incremental signals up to 4,096-fold for measured-value generation. The integrated measured-value memory lets the EIB 741 save up to 250,000 measured values per axis. Internal or external triggers can be used for axis-specific storage of the measured values.

A standard Ethernet interface using TCP/IP or UDP communication is standard for data output. This permits a direct connection to a PC or laptop. The type of measured-value transfer can be selected through the operating mode (transfer of individual values, block transfer, or transfer upon software request).

Driver software for Windows, Linux, and LabVIEW comes with the items supplied to process measured values on the PC. The driver software facilitates programming as well as includes programming examples demonstrating the performance range of the EIB 741.

Heidenhain Corp.

www.heidenhain.us

An open linear encoder

An open linear encoder (no housing on scale) with a built-in mounting control is available. The MS 25 encoder uses a tricolored LED at the reading head letting the user gage whether or not the mounting and subsequent measurement readings are optimal.

The unit is available in North America through parent company Heidenhain Corp.  Common applications for open linear encoders are stages for medical and semiconductor machines, as well as miscellaneous metrology applications.

Open, non-contact linear encoders are increasingly used in applications that require higher traversing speeds and operating cycles, as well as lower mechanical backlash and zero frictional force induced by an encoder. The RSF MS 25 linear encoder fills this bill and with permanent control of the scanning signals over the whole measuring length.  The tricolored LED allows for easy mounting because it needs no test box or oscilloscope, and is helpful for quick troubleshooting during operation.

The encoder uses a single-field scanning principle which allows for traversing speeds to 10 m/s, large mounting tolerances, and insensitivity to contamination on the scale. Interpolation electronics are built into the encoder’s head allowing resolutions from 10 µm to 100 nm. Two end-of-travel optical switch signals are also available directly out of the reader head. The user can set the end travel signal locations.

RSF Elektronik
heidenhain.com
Kevin Kaufenberg
kkaufenberg@heidenhain.com

Encoder tolerates heat, vibration, and shock

The Extreme 1000 series provides encoders for severe environments. The measurement and function range on this Leine & Linde encoder (Available in the U.S. from Heidenhain Corp.,

meets requirements of industries such as wind, steel, crane, and mining machinery. In these applications, the encoder is exposed to extreme mechanical stress, vibrations, shock, and high temperatures.

Sturdy bearings and a rugged enclosure make the encoder useful in all applications with similar demands. The enclosure, rated IP67, protects the encoder’s internal components from dust and liquids. A stainless-steel housing is available as a option.

Different incremental and absolute versions of the 1000 series are available, and of the various encoders can be combined in the same 1000 series product. What’s more, absolute pulse encoders with the Profibus interface can be used in extremely tough industrial environments by using this device. The absolute variants come with interfaces such as SSI, EnDat, CANopen, DeviceNet, or with a parallel output with resolutions up to 25 bit. For more info, reach Tom Wyatt at (847) 884-3713 or twyatt@heidenhain.com.

Encoders Give Turbine Controls More Data

To improve the efficiency of large turbines, many operators have turned to a rather small, 58-mm dia. absolute encoder from Denmark’s Leine&Linde. The Model 500 series of Incremental and absolute encoders provide speed and positioning  feedback to controls in nacelles. Siemens wind turbines, for example, use a pulse encoder on each rotor blade and one to track where the turbine is pointing. The main control system uses position information to optimize generator speed.
Heidenhain Corp
heidenhain.com