Testing force at specific points on the displacement axis with PMX
During a stroke motion with measurement of force and displacement, the force is measured at a specific point on the displacement axis. The measured force must fall within an acceptance band and a good/bad decision will be made. The force is checked once during the outward stroke and once during the return.
In this example the force curve is approximately as follows:
Two "Hold (analog)" glyphs hold the force measured value at point s1. One block during the outward stroke and the other during return. Two limit switches check whether the values are within their respective acceptance band. The rising force is the "press", the falling force the "release". Two digital outputs show the result of the limit switches.
"Press" for rising stroke:
- The measured force value F is retained at point s1=5mm with a "Hold (analog)" glyph. Displacements controls the hold function. It is therefore located at the control input.
- At s=5mm (Lower Limit, Threshold Low) the glyph reads force F and holds it at the output.
- The upper value of the hold range (Upper Limit, Threshold High) is not needed in this case. A dummy value outside of the measuring range is is assigned to it.
- The setting "On entry only" means that the force is read and held exactly one time for each entry into the hold range [5 mm, 999 mm].
For falling stroke "Release":
- The hold range now includes the range s = [-999 mm, 5 mm]; -999 is a dummy value again here. The block holds the measured force value if the displacements at 5mm from above enters into the hold range.
Evaluation by limit switch:
- The outputs of the Hold blocks are the inputs of two limit switches.
- Switch No. 1 report the correct force value for rising stroke. It is active if the "F(5mm) press" signal is within the interval [32 N , 35N].
- The settings for switch No. 2 are similar. The acceptance interval is [26 N, 29 N].
Digital outputs No. 1 and 2 output the states of limit switches Nos. 1 and 2:
- Violation of the acceptance band (as opposed to compliance) can be indicated by inverting the logic, for example with the limit switches.
- Instead of checking the force at points on the displacement axis, of course it is also possible to check displacement at certain points
- Additional direction-dependent check points can also be set up with the appropriate number of Hold blocks.
- Parameter sets can be used to switch the values of the measurement points and/or acceptance bands to other values. A copy of the sub-parameter set Acquisition in which the numeric values are changed has been created for this purpose. Sub-parameter sets are then assigned to different parameter sets, which are switched for example via fieldbus or digital inputs.
Instead of individual numeric values, the structure of calculated channels can also be switched.
The limit switches are switched by the sub-parameter set Limit Switches.
- The task can also be performed with "Trigger (pulse)" and "Hold (digital)" blocks.
These examples are simply for the purpose of illustration. They cannot be used as the basis for any warranty or liability claims.