Local STO on MKD-N

General information (local STO)

The STO safety implementation on the MKD-N is certified. The safety circuit implementation used for the safety function "Safe Torque Off" in the drive is suited for SIL 2 according to IEC 62061 and PLd / CAT3 according to ISO 13849-1.

There is one STO input on X26 and one STO-Status output on X24 for every drive axis.

Enclosure, wiring (local STO)

Avoid pollution of the connectors with conductive obstacles Observe the required ambient conditions.

Overall environment notes and wiring requirements: Enclosure, wiring.

Maximum cable length for safety relevant I/Os and for the 24 V supply is 30 m.

Technical data and connection (local STO)

The local STO input is not compatible with IEC 61131-2. Connector X26 ensures requirements of pollution level 3 according to IEC 60664-1.

STO inputs
  • ON: 18 VDC to 30 VDC, 80 mA
  • OFF: 0 VDC to 12 VDC, < 50 mA
  • Immunity for 60 VDC
  • Tolerated OSSD pulse duration 0.3 ms and minimum pulse duty cycle of 200 ms
  • Galvanic isolation for 250 VDC

STO-Status outputs
  • As per IEC61131-2 type 1
  • Max. 30 VDC, 100 mA
  • Galvanic isolation for 250 VDC

Pinout connector STO input signals

X26 A

Axis 1

X26 B

Axis 2

1

STO +24 V

1

STO +24 V

2

STO +

2

STO +

3

3

4

STO -

4

STO -

5

5

6

STO GND

6

STO GND

Pinout connector STO output signals

X24 A

Axis 1

X24 B

Axis 2

1...3

Digital In 1...3

1...3

Digital In 1...3

4

DCOM

4

DCOM

5...6

Digital Out

5...6

Digital Out

7

STO-Status +

7

STO-Status +

8

STO-Status -

8

STO-Status -

Wiring diagram STO Signals, example

Environment notes and wiring requirements: Enclosure, wiring.

Application example (local STO)

The sample application below shows door guarding and emergency stop, controlled by a safety control to switch the local STO inputs of a dual-axis MKD-N drive module to SIL2, PLd. Both axes strings are switched independently.

Kollmorgen KSM modules cannot be used.
Environment notes and wiring requirements: Enclosure, wiring.

Functional description (local STO)

The STO input releases the power output stage of the drive as long as a 24 V signal is applied to this input. When the local STO function (Safe Torque Off) is not needed, then the STO inputs must be connected directly to +24 VDC. The function is then bypassed and cannot be used.

The global STO signals have no influence to this drive. The local STO input on the MKD-N has no influence to any global STO as well.

Local
STO

String
HW Enable

Local
STO-Status

Safety acc. to SIL2

Drive can
produce Torque

0 V

no

high

yes

no

0 V

yes

high

yes

no

+24 V

no

low

no

no

+24 V

yes

low

no

yes

When STO function is engaged during operation by separating input STO-Enable from 24 V, the connected motor slows down without control.

Local STO-Status is high:

  • during module boot (power up), or
  • if the communication with one of the connected drive modules is lost, or
  • if no drive is connected to the string, or
  • if the local fieldbus doesn't work.

Use the following functional sequence when the STO function is used:

  1. Brake the drive in a controlled manner (speed setpoint = 0 V).
  2. When speed = 0 rpm, disable the drive (enable = 0 V).
  3. If a suspended load is present, block the drive mechanically.
  4. Activate the STO function.

It is not possible to perform a controlled brake if the drive STO input is off.
If controlled braking prior to the use of the STO function is necessary, the drive must be braked first and the STO input must be separated from +24 V time-delayed.

Functional test (local STO)

You must test the safe torque off function after initial start of the drive, after each interference into the wiring of the drive, or after exchange of one or several components of the drive. For dual axis modules you must test every axis separately.

First Method:

  • Stop the drive with setpoint 0 V. Keep drive enabled.

    DANGER: Do not enter hazardous area!
  • Activate the local STO function for example by opening protective screen of the drive, (voltage at input STO = 0V).
  • The drive lose toque and slows down to zero speed without control.

Second Method:

  • Stop the drive with setpoint 0 V, disable drive.
  • Activate the STO function, for example, by opening protective screen (voltage at input STO = 0V)
  • The drive cannot be enabled.