Bosch 6000 User's Guide download pdf (Page 224)

Chapter 6. Following

209

Transfer and

Assignment/

Comparison of Master

Cycle Position and

Number

The current master cycle position and the current master cycle number may be displayed with

the TPMAS and TNMCY commands, respectively. These values may also be read into numeric

variables (VAR) at any time using the PMAS and NMCY commands (e.g., VAR6=NMCY).

Very often, the master cycle number will be directly related to the quantity of product produced

in a manufacturing run, and the master cycle position can be used to determine what portion of

a current cycle is complete.

Position Sampling Period

Steppers – 2 millisec.

Servos –

system update

period

(depends on SSFR

& INDAX command values

– see SSFR command).

The master cycle number is sampled once per position sampling period (see note, left). If the

master cycle length (FMCLEN) divided by the master's velocity (VMAS) is less than the

position sampling period, then the sample (TNMCY or NMCY value) may not be accurate.

Details on using PMAS in conditional expressions is provided below in Using Conditional

Statements with

PMAS

Using Conditional

Statements with

Master Cycle Position

(PMAS)

The current master cycle position (PMAS) value may be used in comparison expressions, just

like other position variables such as PC, PM, PE, and FB. PMAS is a special case, however,

because its value rolls over to zero when the master cycle length (FMCLEN) is met or

exceeded. This means that PMAS values greater than or equal to the master cycle length will

never be reported with the TPMAS command, or with expressions such as (VAR1=1PMAS).

The other fact that makes PMAS special is that master cycle counting may be restarted after the

command containing the PMAS expression has been executed. Either the FMCNEW command or

the TRGFNcx1 command may be used to restart counting, each with a different effect on the

evaluation of PMAS.

The treatment of PMAS in comparison expressions depends on the command using the

expression, as described below. WAIT and GOWHEN are treated as special cases.

IF, UNTIL, and

WHILE

These commands evaluate the current value of PMAS in the same way that TPMAS does (i.e.,

PMAS values will never be greater than or equal to the master cycle length). With these

commands, avoid comparing PMAS to be greater than or equal to variables or constants which

are nearly equal to the master cycle length, because rollover may occur before a PMAS sample

is read which makes the comparison true. If such a comparison is necessary, it should be

combined (using OR) with a comparison for master cycle number (NMCY) being greater than

the current master cycle number.

Also, master cycle counting restart may be pending activation of a trigger, but this will not

affect the evaluation of PMAS for IF, WAIT, and WHILE. It is simply evaluated based on

counting currently underway.

WAIT and GOWHEN

These commands evaluate the current value of PMAS differently than TPMAS does, in such a

way that it is possible to compare PMAS to variables or constants which are greater than or

equal to the master cycle length and still have the comparison be reliably detected.

Effectively, PMAS is evaluated as if the master cycle length were suddenly set to its maximum

value (2

) at the time the WAIT or GOWHEN command is encountered. It eliminates the need to

OR the PMAS comparison with a comparison for master cycle number (NMCY) being greater than

the current master cycle number. Such multiple expressions are not allowed in the GOWHEN

command, so this alternative evaluation of PMAS offers the required flexibility.

This method of evaluation of PMAS allows commands which sequence slave events through a

master cycle to be placed in a loop. The WAIT or GOWHEN command at the top of the loop

can execute, even though the actual master travel has not finished the previous cycle. If it is

desired to WAIT or GOWHEN for a master cycle position of the next master cycle, the variable

or constant specified in the command should be calculated by adding one master cycle length to

the desired master cycle position.

Finally, master cycle counting restart may be pending activation of a trigger (TRGFNcx1),

and this will suspend the evaluation of PMAS for these commands. PMAS is not sampled, and

the comparison evaluates as false. During this time, if the pending status of master cycle

counting restart is aborted with FMCNEWØ, the GOWHEN condition is also cleared, and any

motion profile of any axis waiting on that PMAS comparison will be canceled. Otherwise,

when master cycle counting is restarted by a trigger, evaluation takes place as described above.

This allows GOWHEN to include waiting on a trigger without explicitly including it in the

GOWHEN expression.

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Bosch 6000 User's Guide Page 224

Comments to this Manuals

Bosch 6000 User's Guide Page 224

Comments to this Manuals

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