Servo motor feedback encoder: built-in absolute encoder with a digital drive interface (HIPERFACE DSL, BiSS)

01

20 bit per turn is 1.24 arcsec, but the stated accuracy is ±35 to ±100 arcsec

SICK's EKM36-2KF0B0S03 gives 20 bit resolution per revolution, 4,096 absolutely countable revolutions, a system accuracy of ±100″ and signal noise (σ) of ±5″, by optical measurement. [1] Hengstler's AD36, an optical encoder with a geared multiturn for brushless servo motors, gives 12 to 19 bit singleturn over BiSS (12 to 17 bit over SSI), 12 bit multiturn, ±35″ absolute accuracy and ±7″ repeatability. [2]

Editorial calculation: 2^20 = 1,048,576 steps per turn, or 1,296,000″ / 1,048,576 ≈ 1.24″ per step; at 19 bit a step is about 2.47″. The AD36's ±35″ is about 14 of its 19 bit steps and the EKM36's ±100″ about 80 of its 20 bit steps, so the bit count says how finely the drive can resolve motion, not how close the reported angle is to the true one. A 12 bit multiturn counter, 2^12, equals the 4,096 revolutions SICK states.

The SICK data sheet also lists a measurement step of 262,144 per revolution, which is 2^18, alongside its 20 bit resolution; SICK's safety data give channel 1 as 18 bit or 20 bit. [1] Ask which figure applies to the delivered variant.

RLS's selection table lists a maximum of 17 bit for the smallest readhead and 20 bit for the larger ones, and RLS states that self-calibration removes the eccentricity error of the mounted ring. [3]

02

Drive interface and supply: HIPERFACE DSL on 4 pins at 7–12 V, or BiSS up to 10 MHz

The EKM36 talks HIPERFACE DSL through a 4-pin male connector, runs on 7 to 12 V with 8 V recommended, draws up to 150 mA, outputs the digital position value at 0 to 75 kHz and is ready within 500 ms of reaching its operating voltage. [1] It can also measure an external temperature resistance, NTC or PTC, over −40 to +160 °C. [1]

The AD36 sends fully digital position over BiSS with a variable clock up to 10 MHz, or over SSI together with 2,048 sine-cosine periods per turn at 1 Vpp and a 500 kHz bandwidth for older drives; it runs on 5 V −5 %/+10 % or 7 to 30 V, draws 50 mA singleturn or 100 mA multiturn without load, and reports its own temperature with 8 bit resolution along with warning and alarm bits. [2] The AksIM-2 offers BiSS, asynchronous serial, SPI, PWM or SSI on 4.5 to 5.5 V at 130 mA typical (150 mA maximum), with a 9 kHz bandwidth and up to 44 kHz refresh rate. [3]

Each encoder here lists its own interfaces and supply range; name the drive's encoder interface and supply voltage before choosing the encoder.

03

Inside the motor: up to 115–120 °C, 9,000–10,000 rpm, and SIL2 / PL d where the drive needs it

The EKM36-2 version is rated SIL2 (IEC 61508), SILCL2 (EN 62061), category 3 and PL d (EN ISO 13849) for safe increment, with a PFH of 4 × 10⁻⁸ at 90% diagnostic coverage that the drive must achieve, a mission time of 20 years and an MTTFD of 500 years. [1]

SICK states that the EKM36's EMC ratings apply only when the encoder is mounted in a conductive housing connected to the drive's central earth through the cable screen. [1] RLS rates the AksIM-2 from −40 to +105 °C and lists robot joints with a cable fed through the ring among its uses. [3]

04

Data for a servo motor feedback encoder enquiry

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Motor: [frame size; shaft end (taper, hollow, ring); maximum speed; winding temperature]
Drive: [interface (HIPERFACE DSL, BiSS, SSI, EnDat); supply voltage; cable length]
Position: [singleturn bits; multiturn turns; required accuracy in arcsec]
Safety: [SIL / PL required; safe functions used]
Environment: [shock, vibration; IP rating; motor temperature sensor to be read]

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