Positioning with Digital Outputs (Rapid/Creep Speed)

(Rapid/creep speed)

4-22

4.4.2 Basic configuration of the SFB DIGITAL (SFB 46) 4-27

4.4.3 Jog mode 4-31

4.4.4 Reference-point approach 4-33

4.4.5 Relative incremental approach 4-39

4.4.6 Absolute incremental approach 4-42

4.4.7 Setting the reference point 4-45

4.4.8 Clearing the distance-to-go 4-47

4.4.9 Length measurement 4-49

4.4.1 Positioning with Digital Outputs (Rapid/Creep Speed)

The four 24-V digital outputs (Q0 ... 3) are assigned permanently to the drive controls. Depending on their configured control mode, (refer to Chapter 4.2.3, Page 4-9) these digital outputs control the direction and the speed stages (rapid/creep speed).

Position feedback is realized via an asymmetric 24-V incremental encoder that is equipped with two signal tracks with a 90° phase shift.

Run Start

Start the run with START, DIR_P or DIR_M, depending on the operating mode.

Positioning with Digital Outputs

The upper section of the view below shows the basic run profile. We shall simply assume a linear speed change in proportion to the traveled distance.

The lower part of the figure shows the corresponding profile of the digital outputs.

Rapid and creep speed are determined by a combination of digital output 0 and 1 (refer to Chapter 4.2.3, Page 4-9).

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Rapid speed

Creep speed Digital output

Changeover difference (direction +)

Cutt-off difference ( direction+)

Distance Target range

Target Changeover position

Cutt-off position

Start

WORKING

POS_RCD Vrapid

Vcreep

Velocity

Distance

First, the target is approached at (Vrapid) speed.

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At the changeover point the drive is toggled to creep speed (Vcreep).

The drive is switched off at the cut-off position.

The changeover/cut-off positions are determined for every target approach, using the values specified by you in the parameters Changeover difference and Cut-off difference parameters. The changeover/cut-off difference can be specified differently for positive (Plus direction) and negative (Minus direction) run direction.

The run is terminated (WORKING = FALSE) when the cut-off position is reached. You can then start a new run.

The specified target is reached (POS_RCD = TRUE) when the actual position value reaches the target range. The "Position reached" signal will not be reset

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Working Range

You determine the working range with the help of the software limit switch coordinates. The working range of a synchronized linear axis must never be overrun.

You must always specify the run targets so that they to stay within the working range.

When an axis has overrun the working range, you can only return it in jog mode.

Target range Target

Distance Working range

Software limit switch

Velocity

Monitoring

You can switch various monitoring features on/off individually with the help of the parameter assignment screen forms. The run is canceled if one of the monitoring facilities responds. In this case, an external error (acknowledger with ERR_A) is reported.

Monitoring Description Missing pulse

(zero mark)

When zero mark monitoring is enabled, the CPU monitors consistency of the pulse difference between two successive zero mark signals (encoder signal N).

Missing pulse (zero mark) monitoring is automatically switched off if you have configured an encoder whose output pulses per revolution cannot be divided by 10 or 16, regardless of the setting in the parameter assignment screen form.

The minimum pulse width of the zero mark signal is 8.33 µs (corresponds to a maximum frequency of 60 kHz).

When you are using an encoder whose zero mark is logically "AND" linked to the encoder track signals A and B, the pulse width is reduced by half to 25% of the period.

In order to maintain the minimum pulse width, the maximum counting frequency must be reduced to30 kHz.

Not recognized is:

• Wrong configuration of the number of increments per encoder revolution.

• Failure of the zero mark signal.

Response of the CPU to errors: Delete synchronization, cancel the run.

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Monitoring Description

Travel range The CPU uses travel range monitoring to check whether the permitted travel range of -5x10⁸ to +5x10⁸ is exceeded. This monitoring feature cannot be switched off (always switched on in the "Monitoring" parameter).

Working range The CPU uses travel range monitoring to check whether the actual position value is out of range of the software limit switches.

This facility cannot be switched on for monitoring rotary axis positioning.

This monitoring feature only affects only the synchronized axis.

The actual coordinates of the software limit switch belong to the working range.

Response of the CPU to errors: The run is canceled.

Actual value Within the monitoring time the axis must travel at least by one pulse into the specified direction.

Actual value monitoring is switched on at run start and remains active until the cut-off position is reached.

Actual value monitoring is switched off when the monitoring time is set to "0".

Run is canceled if the monitoring feature responds.

Response of the CPU to errors: The run is canceled.

Target approach

After it has reached cut-off position, the axis must reach the target range within the monitoring time.

Target approach monitoring is switched off when the monitoring time is set to "0".

Response of the CPU to errors: The run is canceled, the outputs are switched off.

Target range After the drive has reached the target range, the CPU monitors whether it remains in the approached position or drifts off.

An external error message is generated if monitoring responds. Monitoring is switched off when you acknowledge the external error with ERR_A (positive edge). Monitoring is not switched on again until the start of a new run.

Response of the CPU to errors: The run is canceled.

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Terminating a Run

The run can be terminated by three different actions:

Target reached

Target approach refers to automatic run termination when the specified target is reached.

The operating modes "Relative/Absolute incremental approach" are used to approach a specified target.

Ramp-Down

The drive is ramped down under following conditions:

In all operating modes, if STOP = TRUE (before the target is reached) In "Jog mode", when stopping and reversing run direction

In "Reference-point approach" mode, when the synchronization position is detected or at direction reversal

The sequences are analogous to target approach.

Cancel

The run is canceled immediately without using the changeover/cut-off difference by switching off all relevant outputs of the corresponding control mode.

A current run can always be canceled during operation or standstill of the drive.

A run is canceled under following conditions:

When the drive enable signal is deleted (DRV_EN = FALSE) When the CPU switches to STOP mode

When an external error occurs (Exception: monitoring of target approach/range)

Reactions:

The current or interrupted run is terminated immediately (WORKING = FALSE).

The last target (LAST_TRG) is set to the actual value (ACT_POS).

The distance-to-go is deleted, that is, "Relative incremental approach" cannot be resumed.

"Position reached" (POS_RCD) is not set.

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