Linear encoders respond to movement along a path and measure position and speed during linear movement or displacement. The linear encoder reads the scale and converts the encoded position to an analogue or digital signal. A motion controller decodes the signal and converts it into a position.
Absolute and incremental signals
Linear encoders can send absolute signals (unique code per pulse) and incremental signals (pulse is given value '1' vs '0' for non-pulse). Linear encoders are used in metrology instruments, motion systems and high-precision machining tools.
When finding the right encoder, the key questions are:
- What is to be measured?
- Under what conditions will be measured?
- What is the communication level of the encoder?
- What length or distance is decisive for the encoder?
Measurement technologies linear encoders
Optical linear encoders
Optical linear encoders are mainly used in industrial automation processes. Optical linear encoders are the most accurate encoders of standard styles. Additional protection is important for an optical linear encoder. The linear encoder must be able to withstand dust, vibration and other conditions found in industrial environments.
Magnetic linear encoders
Magnetic linear encoders have coarser scale periods than optical linear encoders. Magnetic linear encoders use active (magnetised) or passive (variable reluctance) scales. Position can be measured using sense-coils, Hall effect or magnetoresistive readheads.
Capacitive and inductive linear encoders
Capacitive linear encoders detect the capacitance between a reader and scale. Capacitive linear encoders are mainly used in digital calipers. A disadvantage of capacitive linear encoders is their sensitivity to uneven dirt. This can change the relative dielectric constant locally. Inductive linear encoders are robust to contamination, making calipers and other measuring instruments coolant-resistant.
Programmable linear encoders
Lika Electronic's SME54 an incremental magnetic strip. The incremental linear encoder offers engineers a fully programmable solution. The resolution can be set in the range 1.25mm - 0.08μm along with the duration and count of the index mark direction. The SME54 incremental encoder offers full customisability, versatility and freedom for any type of industrial application. Configuration is possible via PC software.
Dust, oil and liquid-proof (IP67)
Dust, oil and liquid-resistant (IP67) The large allowable tolerances and air gap (up to 2 mm) allows easy installation and minimum assembly time. They generate quadrature signals with inverted signals and index signals via Push-Pull (HTL) and Line Driver (TTL) output circuits and feature diagnostic LEDs as standard.
Advantages of linear encoders
In a number of applications, a linear encoder with magnetic sensor technology is preferred over a rotary encoder. Linear encoders with magnetic sensor technology take over perception, so operate without contact which ensures wear- and maintenance-free operation. Linear encoders have no moving parts and almost all the mechanical components installed on the rotary encoder do not have the linear encoder. The limited use of both mechanical and miniaturised circuits minimise the overall footprint of the devices.
Linear encoders with magnetic technology are highly immune to external influences such as light, oil, grease, water, chemical contamination, etc. and makes it easy to apply PCB protection methods such as encapsulation, tropicalisation, conformal coating and varnishing. In this way, the linear encoders achieve protection levels of IP67 and IP69K and operate reliably in the harshest industrial environments.
Another advantage of linear encoders is their modular structure. The encoders consist of a readhead and a magnetic tape that are not in contact with each other. The risk of errors and malfunctions due to vibrations, shocks and mechanical stresses are limited.
Linear encoder for small dimensions - Best resolution - Greatest accuracy
The SMA2 linear encoder is ideally suited for positioning and fast feedback applications where small size, best resolution and highest accuracy are mandatory. The linear encoder offers a high resolution of up to 1 μm and a high accuracy of ± 2 μm. The maximum measurement length is 8.1 m and the maximum speed is 10 m/s. The encoder is accompanied by an MTA2 double-track magnetic tape, so it can provide both the absolute information for position feedback via the BiSS-C and SSI interfaces and the additional information for speed feedback via the NPN output circuit.
Linear encoder properties: SMA2
SMA2 is also excellent in its mechanical properties: although the sensing head is very compact and slim, it retains its toughness. The fully encapsulated electronics are optimally protected against dust, oil, grease, water, shock, vibration. Typical applications include linear motors, pick & place robots, electronic assembly systems.