Closing the Loop

Linear and rotary encoders provide critical feedback information for motion control systems. Long life, even in a harsh operating environment, lower cost and high-speed operation, including high-speed networking capabilities, are key trends for these products. However, business aspects such as lead times can provide important design consideration as well. “Machine designers frequently don’t know the exact encoder configuration until late in the design process, let alone getting it ordered, so quick delivery can really be critical,” says Joe Schwartz, sensors division director, TURCK Inc. Six feedback sensors demonstrate these trends.

LINEAR POSITION ENCODER FAMILY

OEMs needing to improve rotary encoder accuracy at the motor shaft can now use Balluff’s BML linear position encoder. Regardless of the mechanical wear or actuator backlash, the encoder offers more accurate direct measurements of the load’s linear position than indirect rotary encoder-based positioning systems. Floating above a precision-encoded magnetic band, the sensing head provides an incremental position reference to the sensing electronics and up to 24 meters of non-contact, wear-free position tracking up to 10 m/s with no signal degradation over time. The encoder is available in two models. The S1A model has a maximum resolution of 1 µm and maximum system accuracy of ± 10 µm with a gap up to 0.34 mm. The S1B provides resolution of 5 µm and maximum system accuracy of ± 50 µm with a gap up to 2.0 mm. BML encoders are designed for packaging sequences for metalwork, automotive, material handling and electronics, as well as wood processing.

RUGGED LINEAR ENCODER

The LN series linear encoder from BEI linear offers a rugged design with IP67 environmental ratings, a stainless steel scale and a sealed read head, which reduce system downtime and breakage risk. The encoder provides accurate and repeatable position feedback with resistance to contaminants, vibration and shock. Based on a non-contact measurement system, the LN series has no parts to wear out and requires no air purging system allowing it to operate in harsh industrial environments where even liquids and debris will not affect its performance. The encoder scale measuring lengths range from 2 inches to 36 ft with resolutions of 0.5 to 10 µm. Operating between 5 and 28V dc, units are equipped with either open collector outputs or a line driver. For easy system integration, the encoders have universal mounting adapters and standard electrical interfaces. The LN linear encoders focus on pick and place operations, automated processes, and machine control among other applications.

EXPOSED LINEAR ENCODER

Targeting low-end linear motors, the LIDA 200 series of encoders from HEIDENHAIN offers two simple mounting methods. The exposed linear encoders’ coarser gratings provide improved resistance to contamination, such as scratches and fingerprints, and can be quickly mounted with scale adhesive tape or a scale tape carrier extrusion. The linear encoder package operates at 10 m/sec. Even though accuracy requirements in the low-end applications are considerably less than high-end applications, analog systems have grating period of 200 µm and available digital systems have signal periods of 5, 1 and 0.5 µm.

HEAVY DUTY ENCODER

With a high shock rating of 250g, TURCK Inc.’s T8.5000 and T8.5020, Kübler by TURCK, encoders have a captive bearing design and up to a 12,000 RPM speed rating with 300 kHz frequency response. Based on an optional shaft seal, the units provide IP 67 protection for harsh applications and have resolutions of up to 3,600 pulses per revolution. The T8.5000 has a 2-inch incremental shaft and the T8.5020 has a hollow shaft. Both are available with several output circuits and bore sizes. The Kübler T8.5000 and T8.5020 focus on industrial applications where space is limited, such as process and Web control, material handling and conveyors systems. Now assembled in the U.S., the Kübler allows customers to buy a reliable encoder with a captive bearing design with lead times comparable to or better than other standard encoders.

CANOPEN INTERFACE ENCODER

Operating in high shock and vibration environments, the ATM 60-C multi-turn absolute encoders from SICK STEGMANN INC. provide up to 26 bits resolution, have a CANopen interface and are electronically adjustable. The interface is Communication Profile DS 301 V4.0 with Device Profile DSP 406 V2.0. With a supply voltage from 10 to 32V, the programmable resolution is 13 bits per turn times 8,192 turns for 26 bit maximum. Available with face mount flange, servo flange or blind hollow shaft connections, the encoders are IP67 rated. Bore/Shaft size and mounting are 6 mm with servo mount or 10 mm with face mount and 15 mm hub shaft with integral flex mount and collets for 6, 8, 10 or 12 mm and 0.25, 0.375 or 0.5 inch. The ATM 60-C targets operation in environments with high shock and vibration, such as machine tool, textile, woodworking and packaging machinery and wind turbines among others.

INDUSTRIAL ETHERNET POSITION FEEDBACK SENSOR

MTS Sensors R-Series EtherCAT sensor is a high-speed networking solution based on industrial Ethernet technology. An Ethernet for Control Automation Technology (EtherCAT) sensor provides fast, deterministic industrial networking using the base Ethernet physical layer. Enabling high-speed data transfer between the plant floor and office to assist with statistical process control and computer aided design automation, the R-Series sensor can also synchronize to accurate clock signals, enabling high-speed deterministic control. Designed for use with one to five position magnets, depending on the particular network, the sensor can be customized to document position, velocity, and acceleration, as well as additional customer-specified functions. With position resolution accurate to 1 µm, speed to 0.2 mm/sec (0.008 inch/sec) and a sensor update time of 100 µs (independent of stroke), the sensor also includes a built-in non-linearity correction option for position accuracy as low as ±0.02 mm (0.0008 inch).