Posted on May 17, 2011 at 10:18hello to everybody,
we are standing for the decision to use the ST7MC in our control system for
a linear drive with a one phase inverter. Because I am not familiar with the ST7MC
I can not estimate whether the ST7MC is quick enough for our task like the
following:
- Controlling a linear drive which is controlled by a H-bridge on the power side.
- We need for the controlling of this motor a positioning control-loop and a
current control-loop.
- The sensor for the position recognition consists of a optical incremental
photoelectric barrier with 2 tracks and an additional similar optical sensor
for a index track.
The numbers of the total read-in increments of both tracks together correspond to
11 bits and the frequency of the edges of the increments is approximately 55kHz.
In order to realise the direction of moving of the slide or armature of the
linear motor we need the up/down reversing function of the 16-bit-timer in
connection with the quadrature decoder function of the ST7MC.
The index signal has a frequency of approximately 48Hz.
- The sensor for the current is a shunt resistor which measure the DC-link current
into the inverter. The current sampling frequency is 4 kHz ( fix time slice ) with
the resolution of 10 bit. The PWM-frequency of the current for switching the H-bridge
should be up to 16 kHz in order to avoid noise problems ( at least 12kHz ).
We will use the built-in operation amplifer for amplify the current signal from
the shunt resistor.
- At least 3 processes are running at the same time via interrupt service routines
1. Increments read-in/moving recognition/up/down-counting is working parallel
to the ST7MC. Correction of the counter value one time per cyclus via index-signal.
Results yield the setting values for the current control.
2. In a fix time slice: Current value read-in via AD-converting .
Calculating the control value(Proportional Integral structure)
3. Current value set the auto reload PWM-Timer in the called fix time slice.
- Additional we have still a asynchronous communication with a PC-host (lowest
priority in main loop)
I still hope that the ST7MC is adequate for the described task.
Or in the case of emergency which time values in the loops have I to consider to reduce in order to keep the present concept.
Many thanks in advance.
hakl
