Homing

The purpose of the homing method is to align the position zero point of the controller with an encoder index or position switch.

To activate the mode, the value "6" must be set in object 6060_h (Modes Of Operation) (see "CiA 402 Power State Machine").

The following bits in object 6040_h (controlword) have a special function:

• Bit 4: If the bit is set to "1", referencing is started. This is performed until either the reference position is reached or bit 4 is reset to "0".

The following bits in object 6041_h (statusword) have a special function:

The following objects are necessary for controlling this mode:

• 607C_h (Home Offset): Specifies the difference between the zero position of the controller and the reference point of the machine in user-defined units.

• 6098_h (Homing Method):

  Method to be used for referencing (see "Homing method")

• 6099_h:01_h (Speed During Search For Switch):

  Speed for the search of the switch

• 6099_h:02_h (Speed During Search For Zero):

  Speed for the search of the index

• 6080_h (Max Motor Speed): Maximum speed

• 609A_h (Homing Acceleration):

  Starting acceleration and braking deceleration for homing

• 203A_h:01_h (Minimum Current For Block Detection):

  Minimum current threshold which, if exceeded, is to detect the blocking of the motor at a block.

• 203A_h:02_h (Period Of Blocking):

  Specifies the time in ms that the motor is to continue to run against the block after block detection.

The homing method is written as a number in object 6098_h and decides whether, on a switch edge (rising/falling), a current threshold for block detection or an index pulse is referenced or in which direction homing starts. Methods that use the index pulse of the encoder lie in the number range 1 to 14, 33 and 34. Methods that do not use the index pulse of the encoder lie between 17 and 30, but are identical to methods 1 to 14 with respect to the travel profiles. These number are shown in circles in the following figures. Methods for which no limit switches are used and, instead, travel against a block is to be detected, a minus must be placed before the method number when making the call.

In the following graphics, the negative movement direction is to the left. The limit switch is located before the respective mechanical block; the home switch is located between the two limit switches. The index pulses come from the connected encoder.

For methods that use homing on block, the same figures apply as for the methods with limit switch. Because nothing is different aside from the missing limit switches, the same figures are used. For the figures here, the limit switches must be replaced with a mechanical block.

Homing on block currently only functions in closed loop mode.

"Homing on block" functions like every homing method with the difference that instead of a limit switch, a block (limit stop) is used for positioning. Two settings are to be made here:

Methods 1 to 14 as well as 33 and 34 use the index pulse of the encoder.

Methods 17 to 32 are identical to methods 1 to 14 with the difference that only limit or home switches are used for referencing and not the index pulse.

• Methods 1 to 14 use an index pulse.
• Methods 17 to 30 do not use an index pulse.
• Methods 33 and 34 reference only to the next index pulse.
• Method 35 references to the current position.

Reference to limit switches and index pulse.

Method 1 references to negative limit switch and index pulse:

Method 2 references to positive limit switch and index pulse:

Reference to the switching edge of the home switch and index pulse.

With methods 3 and 4, the left switching edge of the home switch is used as reference:

With methods 5 and 6, the right switching edge of the home switch is used as reference:

Reference to the home switch and index pulse (with limit switches).

With these methods, the current position relative to the home switch is not important. With method 10, for example, referencing is always performed to the index pulse to the right of the right edge of the home switch.

Methods 7 to 10 take the positive limit switch into account:

Methods 11 to 14 take the negative limit switch into account:

Reference to the limit switch without the index pulse.

Method 17 references to the negative limit switch:

Method 18 references to the positive limit switch:

Reference to the switching edge of the home switch without the index pulse.

With methods 19 and 20 (equivalent to methods 3 and 4), the left switching edge of the home switch is used as reference:

With methods 21 and 22 (equivalent to methods 5 and 6), the right switching edge of the home switch is used as reference:

Reference to the home switch without the index pulse (with limit switches).

With these methods, the current position relative to the home switch is not important. With method 26, for example, referencing is always performed to the index pulse to the right of the right edge of the home switch.

Methods 23 to 26 take the positive home switch into account:

Methods 27 to 30 take the negative home switch into account:

Reference to the next index pulse.

With these methods referencing is only performed to the respective subsequent index pulse:

References to the current position.