Bosch 6000 User's Guide download pdf (Page 116)

Chapter 3. Basic Operation Setup

101

Commanded Direction Polarity

EXAMPLE:

The command to

change the polarity for

axis 2 is CMDDIR,1

The CMDDIR command allows you to reverse the direction that the controller considers to be

the “positive” direction; this also reverses the polarity of the counts from the feedback devices.

Thus, using the CMDDIR command, you can reverse the referenced direction of motion

without the need to (a) change the connections to the drive/valve and the feedback device, or (b)

change the sign of all the motion-related commands in your program.

NOTES

• The CMDDIR command cannot be executed while motion is in progress or

while the drive/valve is enabled. For example, you could wait for motion to be

complete (indicated when TAS and AS bit #1 is a zero) and then use the DRIVE command to

disable the appropriate axis before executing the CMDDIR command.

• Before changing the commanded direction polarity, make sure there is a direct correlation

between the commanded direction and the direction of the feedback source counts (i.e., a

positive commanded direction from the controller must result in positive counts from the

feedback device). Refer to the ANIPOL, ENCPOL, or LDTPOL command descriptions for

further information.

• Once you change the commanded direction polarity, you should swap the end-of-travel

limit connections to maintain a positive correlation with the commanded direction.

• The CMDDIR command is automatically saved in non-volatile memory (stand-alone

products only).

• The CMDDIR command is not implemented in the AT6n50 and 625n products.

Dither

Dither is a square-wave signal added to the analog output and is used to keep the motor or the

hydraulic valve moving slightly for the purpose of reducing stiction (see illustration below).

Two commands are used to select the amplitude and frequency of the dither signal—SDTAMP

and SDTFR.

SDTAMP

Analog

Output

SDTFR

SSFR (servo sampling frequency)

SDTFR = Dither Frequency (cycles/sec)

Dither

Square Wave

Signal

☞

Refer to the SSFR

command description or

the

Servo Tuner User

Guide

for a discussion on

the servo sampling rate.

The SDTAMP command selects the amplitude of the dither signal in peak volts (see

illustration). The SDTFR command selects the frequency ratio of the dither.

The actual dither frequency is determined by the ratio of the servo sampling frequency (SSFR &

INDAX settings) and the SDTFR value. As an example, if the SSFR value is 4 and the INDAX

value is 2, the servo sampling rate is 3571 samples per second. Then, at SSFR4, an SDTFR

value of 46 (default setting) would yield a 77 Hz dither frequency (3571/46 = 77). With an

SDTFR command setting of 46, a positive voltage (SDTAMP) is added during 23 servo updates

and a negative voltage is added during the next 23 servo updates.

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Bosch 6000 User's Guide Page 116

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