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Open loop motion control
12.5 Configuring an Axis of Motion
S7-200 SMART
616
System Manual, V2.3, 07/2017, A5E03822230-AF
Configuring reference point and seek parameters
1. Select using a reference point or not using a reference point for your application:
–
If your application requires that movements start from or be referenced to an absolute
position, you must establish a reference point (RP) or zero position that fixes the
position measurements to a known point on the physical system.
– If a reference point is used, you will want to define a way to automatically relocate the
reference point. The process of automatically locating the reference point is called
Reference Point Seek. Defining the Reference Point Seek process requires two steps
in the wizard.
2. Enter the Reference Point seek speeds (a fast seek speed and a slow seek speed):
–
RP_FAST is the initial speed the module uses when performing an RP seek
command. Typically, the RP_FAST value is approximately 2/3 of the MAX_SPEED
value.
– RP_SLOW is the speed of the final approach to the RP. A slower speed is used on
approach to the RP, so as not to miss it. Typically, the RP_SLOW value is the
SS_SPEED value.
3. Define the initial seek direction and the final reference point approach direction:
–
RP_SEEK_DIR is the initial direction for the RP seek operation. Typically, this is the
direction from the work zone to the vicinity of the RP. Limit switches play an important
role in defining the region that is searched for the RP. When performing a RP seek
operation, encountering a limit switch can result in a reversal of the direction, which
allows the search to continue. (Default = Negative)
– RP_APPR_DIR is the direction of the final approach to the RP. To reduce backlash
and provide more accuracy, the reference point should be approached in the same
direction used to move from the RP to the work zone. (Default = Positive)
4. The Motion wizard provides advanced reference point options that allow you to specify an
RP offset (RP_OFFSET), which is the distance from the RP to the zero position. See the
following figure:
–
RP_OFFSET: Distance from the RP to the zero position of the physical measuring
system.
– Default = 0