IEC 61508 Functional Safety Standard SIL3 compliant

MAR-M40AS and MAR-MK42AS multi-turn absolute encoders released

December 1, 2015

Nikon Corporation (Kazuo Ushida, President, Minato-ku, Tokyo) is pleased to announce the release of two multi-turn absolute encoders*1, the MAR-M40AS and the MAR-MK42AS, that are compliant with the IEC 61508 SIL3 functional safety standard*2. The encoders obtain position information from two independent sources and provide safety motion monitoring for on-board robots.

The encoders will be displayed at the upcoming 2015 International Robotics Exhibition at Tokyo Big Sight from 2 to 5 December.

Product information

Product Name MAR-M40AS and MAR-MK42AS absolute encoders compliant with functional safety standards
Price Open price
Available from December 1, 2015
Left : M scale of internal structure
Right : Exterior view


1. Superior safety performance

Used in combination with a robot motion safety monitoring unit, the safety performance of the overall system including the encoder is IEC61508 SIL3 and ISO13849-1*3 PLe/Cat. 4 (safety category 4) level. The encoder in isolation provides safety performance at IEC61508 SIL2 and ISO13849-1 PLd/Cat.2 (safety category 2) level.

2. Duplex position information (position information Pos1 and Po2)

The encoder obtains position information from two independent internal systems (single turn and multi-turn) and forwards the position information to the higher-order controller in the Nikon A-Safety duplexed format. This approach allows safety motion monitoring without the need for two separate encoders. Duplex position information also enables detection of multi-turn errors in robot system stopped status (encoder backup operation status) which was not possible previously.
[See internal system diagram of encoder below.]

3. Backward compatibility to support upgrading

Mechanical parts are inherited from the MAR-M40 series and MK32 series. This ensures compatibility with motors for easy upgrading and replacement.

4. Maximum transmission speed of 16 Mbps

The M40AS and MK42AS boast transmission speeds of up to 16 Mbps, a significant improvement over the 4 Mbps maximum baud rate of previous models. (optional)

Internal system diagram

Main specifications

Basic specifications

Resolution Pos1
 Single turn
 Multi turn

20 bit (1,048,576P/R) / 17 bit (131,072P/R)
16 bit (65,536P/R)
 Single turn
 Multi turn

3 bit (8P/R)
16 bit (65,536P/R)
Responsive revolution speed Normal operation 6,000 min-1 (up to 7,200 min-1 with option)
Backup battery 10,000 min-1
Power source Normal operation DC 5V ±5%
Backup battery DC 3.6V (ER battery)
Current usage (under normal operating conditions) 130 mA (TYP)
Current usage (with external battery backup) 45μA (TYP)
Operating temperature range
 Without electric double layer capacitor
 With electric double layer capacitor

Dimensions External diameter M40AS:φ35 mm /MK42AS:φ60 mm
Height M40AS:13.4 mm (TYP)/ MK42AS:23 mm (TYP)

Mechanical specifications

Moment of inertia for shaft M40AS:3.24x10-7 kg⋅m2
MK42AS:2.54x10-6 kg⋅m2
Allowed rotational angular velocity 1.0x105 rad/sec2

Communication specifications

Transmission standard EIA standard RS-485 compliant
Transmission method NRZ code half-duplex serial transmission
Transmission protocol Nikon A-Safety format (to Nikon A format safety technical specifications)
Baud rate 2.5 Mbps (with options for 4 Mbps, 6.67 Mbps, 8 Mbps and 16 Mbps)
Number of signal lines 4 (or 6)
With optional bus connection Supports encoders for up to 8 axes

The information is current as of the date of publication. It is subject to change without notice.