W.E.S.T. Elektronik POS-123-P-PFN, Техническая документация инструкция

Страница: 12 / 53

Page 12 of 53 POS-123-P-PFN 31.03.2021
3.2.2 Influences on positioning accuracy
The positioning accuracy is determined by the hydraulic and mechanical conditions. The right choice of valve
is therefore a decisive factor. In addition, two mutually contradictory requirements (short position time and high
accuracy) must be taken into account when designing the system.
The electronic limitations lie mainly in the resolution of the analogue signals, although a resolution of
< 0,01 % only needs to be considered for our modules with long positions. In addition, the linearity of the
individual signal points (PLC, sensor and control module) must be taken into account.
It is generally recomended to calculate the static and dynamic behavior of the hydraulic axis. For supporting
this, following technical basic data are required:
- minimum natural frequency of the cylinder,
- maximum theoretical speed for extending and retracting,
- valve characteristics (natural frequency, overlapping, hysteresis and the flow gain (flow and pressure
drop),
- system pressure, maximum pump flow,
- and a description of the general system requirements.
3.2.3 Optional additional function: motion profile with second speed
Because of the input of a second position and speed, the axis can be driven to this position with the second
velocity. This mode is only activated when the velocity command value V2 is not equal to zero.
The following features have to be noticed:
•
The position command value (P2) is the end position that is approached with the velocity (V2).
•
The position setpoint (P1) is the switching position, which is approached with the speed (V1) and then
switched over to the speed (V2).
•
The speed is switched via the speed ramp (in NC mode via the acceleration).
•
If the position setpoint (P2) is between the feedback value and the position setpoint (P1) (P1 and P2 are
reversed), the position (P2) is started at speed (V1).
The following illustrations show two possible speed profiles, which result depending on the choice of speed V2
in relation to V1:
time / position
ve
lo
ci
ty
P1
P2
V1
V2
acceleration
P1
P2
V1
V2
acceleration deceleration
High to low speed
Low to high speed
ve
lo
ci
ty
time / position
deceleration