New ways to keep track of shaft positions
14 November 2009
Encoders are beginning to shed some of their older mechanical parts, such as gears, and take on new technologies such as AMR (Anisotropic-Magneto-Resistive effect) which has been used in computer disc drives for some time. Applications in extremely harsh industrial and outdoor environments appear to be the current goal of these new products. Manufacturers stop short of saying they will last forever, but for sure, they are much more durable and can be used in more inhospitable conditions.
Kübler boasts their new generation of Sendix F36 encoders (right) ‘must surely make potentiometers a thing of the past.’ On the left is a “bulletproof” stainless steel incremental encoder.
Kübler, for example, says its Sendix F36 multiturn optical encoder is the first one it has built without gears and a battery, which gives it a service life unmatched by any other product. The construction makes it a more compact unit, and at the same time minimises technological disadvantages such as wear and ageing or magnetic sensitivity.
The bearing assembly, which accounts for the extreme ruggedness and long service life, takes up two-thirds of the overall depth of the encoder.
The total resolution is up to 41 bits, a combination of a programmable multi-turn encoder with up to 16 million revolutions and a high-precision single-turn with up to 17 bits resolution. Kübler boasts their new generation of encoders ‘must surely make potentiometers a thing of the past.’
Left: Balluff’s S2E Rotary BML provides a quadrature output at up to 46,000 pulses per revolution. Right: Pepperl+Fuchs’ magnetic incremental rotary encoder.
For those who like it especially rough, Kübler has also launched a stainless steel Sendix, an incremental coder that, with its high-grade Viton seals and sturdy Safety-Lock™ design, has ‘almost unlimited service life.’
Long life – even at high speeds
Pepperl+Fuchs’ Type MN140 Incremental Rotary Encoder was designed for applications in which dirt, dust and moisture abound. The development engineers housed the sensor element, including the interface electronics, in a highly compact encapsulated enclosure with IP67 protection. Contact with water, oil and dirt are of no consequence.
The foundation of the magnetic measuring system is the result of knowledge gained from the latest AMR/GMR technology, which is the same technology used in computer disc drives. The zero-contact connection of sensor and magnet wheel eliminates ball bearings which automatically guarantees a longer life, even at high rotational speeds of up to 30,000 revolutions per minute.
The LIC 4000 absolute linear encoder from Heidenhain is “insensitive to contamination.”
It is available with a resolution of up to 3,200 pulses per revolution. The high maximum output frequency is 1 MHz, so that the accommodation of high rotational speed is not only mechanically possible, but also electrically achievable with high resolution. In the current standard series a wide range version for 10…30 V is also available in addition to the 5 V version.
Another magnetic encoder to hit the market is the S2E Rotary BML encoder from Balluff. The basic design consists of a magnetically-encoded ring and, again, a non-contact sensor head. This assembly is said to install easily and provides a quadrature output at up to 46,000 pulses per revolution.
The IP67 instrument was designed especially for accurate velocity and position tracking of virtually any rotary movement—continuous or oscillating rotary shaft motion. In conveyor applications, for example, it gives a PLC the position information necessary for virtually all operational functions such as multiple station error proofing with single station rejection. It also provides conveyor speed control monitoring. Position information provided by the S2E can also be used by the central PLC to develop software driven programmable cams. With the IP67 rating it can be used in outdoor applications, such as controlling the rotational positions of solar reflectors.
Renishaw’s FASTRACK track-mounted linear encoder scale system, ideal for large machines.
Heidenhain introduced its LIC 4000 encoder this summer. According to the company, its specialised scanning technologies are ‘insensitive to contamination and therefore guarantee a high degree of equipment availability and a high traverse speed, while at the same time achieving a high resolution of one nanometre.’ These EnDat 2.2 encoders feature up to 27 meters of measuring length.
Absolute encoders, which provide the current position immediately upon switch-on, offer high technological reliability and safety because they can operate without the reference runs that would otherwise be necessary. Absolute encoders also are especially well suited for use on direct drives.
Together with the current position, the commutation offset is known immediately upon switch-on and the motor can immediately be provided with power and held in the control loop.
Their dimensions match those of Heidenhain’s existing Lida 400 incremental linear encoder, making it easy to retrofit existing machine tools, providing absolute measurement technology by just exchanging the encoders.
Glue this scale where you want it
This FASTRACK track-mounted linear encoder scale system from Renishaw is said to be ideal for large machines that need to be sectioned for transportation to their installation site. It is supplied on reels, and cut to length and glued to the substrate between self-adhesive guide rails. Installers use separate sections and allow the scale to run across the joins (the gaps can be up to 25 mm), safe in the knowledge that the scale can be installed, removed and re-installed as many times as required. It combines ±5 um/m accuracy with the ruggedness of stainless steel.
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