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116

Digitax HD M753 Control User Guide

Issue Number: 3

Table 9-88 0x604C vl_dimension_factor

The

vl_target_velocity

object is re-read every new profile cycle. It is

scaled to appropriate units using the

vl_dimension_factor

and

vl_setpoint_factor

objects and then written to the drive preset

reference 1 parameter (Pr

01.021

The object

vl_velocity_min_max

is handled every profile cycle.

The

vl_target_velocity

is limited according to the values set in the object

vl_velocity_min_max

, which is read every profile cycle. The object

vl_velocity_min_max_amount

is mapped to

vl_velocity_min_max

The value of the

vl_velocity_demand

object is calculated in the

background. The option reads the value of parameter Pr

02.001

(post ramp reference), scaled from RPM to user units using

vl_dimension_factor

and

vl_setpoint_factor

, and writes the value to the

vl_velocity_demand object

On a closed-loop drive, the speed feedback is calculated internally every
profile cycle, scaled to the same units as

vl_target_velocity

and written to

the

vl_velocity_actual_value

object. On an openloop drive, the estimated

motor speed is read from Pr

05.004

(motor RPM) in the background,

scaled to the units of

vl_target_velocity

and written to the

vl_velocity_actual_value

object.

The

vl_velocity_acceleration

and

vl_velocity_deceleration

objects are

handled in the background. They are read, scaled to drive acceleration
units (depending on the drive operating mode), and written to the drive
acceleration rate and deceleration rate presets. In addition, if the drive
acceleration rate preset is changed, the

vl_velocity_acceleration

object

is updated, and if the drive deceleration rate preset is changed
(Pr

02.021

), the

vl_velocity_deceleration

object is updated.

9.21

Homing mode

This section describes the method by which a drive seeks the home
position (also called, the datum, reference point or zero point).
Figure 9-9 shows the defined input objects as well as the output objects.
The user may specify the speeds, acceleration and the method of
homing. There is a further object named home offset, which allows the
user to displace zero in the user's coordinate system from the home
position.
There is no output data except for those bits in the statusword, which
return the status or result of the homing process and the demand to the
position control loops.

Figure 9-9 Homing mode function

By choosing a homing method the following behavior is determined:
The homing signal (home switch), the direction of actuation and where
appropriate the position of the index pulse.
An encircled number in Figure 9-10 to Figure 9-15 indicates the code for
selection of this homing position. The direction of movement is also
indicated.
There are two sources of homing signal available: These are the home
switch and the index pulse from an encoder.

9.21.1

General homing definitions

Method 3 and 4: Homing on positive home switch and index pulse

Using these methods as shown in Figure 9-10

Homing on positive home

switch and index pulse

on page 116, the initial direction of movement

shall be dependent on the state of the home switch.
The home position shall be at the index pulse either to the left or the right
of the point where the home switch changes state. If the initial position is
sited so that the direction of movement shall reverse during homing, the
point at which the reversal takes place is anywhere after a change of
state of the home switch.

Figure 9-10 Homing on positive home switch and index pulse

Method 5 and 6: Homing on negative home switch and index pulse

Using these methods as shown in Figure 9-11

Homing on negative

home switch and index pulse

on page 116, the initial direction of

movement shall be dependent on the state of the home switch.
The home position shall be at the index pulse either to the left or the right
of the point where the home switch changes state. If the initial position is
sited so that the direction of movement shall reverse during homing, the
point at which the reversal takes place is anywhere after a change of
state of the home switch.

Figure 9-11 Homing on negative home switch and index pulse

0x604C

vl_dimension_factor

Sub-index 0
Access: RO

Range: N/A

Size: 1 byte

Unit: N/A

Default: 2

Type:

USINT

Description:

The number of sub-indices in this object.