Specifications

Chapter 1
Introduction
A cost-efficient alternative for the widely used but expensive dSPACE systems has to be created.
The Data Acquisition and Control System (DACS) in the "light-weight positioning" project is used as
a carrier for this task. Within this project lies the scope of this traineeship. The DACS specifications
for this project are taken as an example, but the use should not be limited to this project.
The DACS is developed for rapid control prototyping of mechanical systems. This implies that
sample rates for acquiring, computing controller actions and sending data should be typically a couple
kHz. After selecting the proper hardware it was optimized
1
by modifying the drivers. The system will
also need multiple in- and outputs to satisfy the goal of the initial application. For information about
the hard- and software used see, appendix B.
What is needed? The specification for the DACS are given below in more detail:
• Performance
– High execution sample rate, i.e. at least 10[kHz],
– achieved for at least 8 in- and 8 outputs,
– while using fairly complex centralized controllers.
• Execution of Simulink models in Hard Real-Time.
• Interface to Simulink enabling "on-the-fly" parameter changes.
What is available: an impression Three commonly known DACSs, who can satisfy these speci-
fications, are described. First there is dSPACE or other systems from manufacturers like National
Instruments (NI) or Quanser which are commercially available DACSs. Then there is xPC and finally
DACSs alike ours, which use a host-CPU with DAC/ADC boards and a Real-Time Operating System
(RTOS). All three are compatible with Matlab Simulink.
Firstly, well known DACSs are those manufactured by dSPACE [2], NI [5] or Quanser [8]. All
manufacturers use their own software interface to communicate with the Real-Time executable Maltab
Simulink program. Within these programs, model parameters can be changed "on-the-fly". The Real-
Time executable runs on its own CPU. Achieving the performance specifications is merely a matter of
price. These solutions are expensive, an extra interface has to be customized for each experiment, but
performance is guaranteed!
Secondly, the xPC uses two PC’s with a network connection in between, one host-PC for the inter-
face and one master-PC to run the Real-Time executable. In this way it acts a little like the previous
products. The master-PC needs (cheap) DAC/ADC boards, which are readily available or an xPC-box
can be used instead from the manufacturer of Matlab. Again interface software, an extra Matlab-
toolbox, needs to be purchased. And it offers reduced flexibility, due to a slow rebuild procedure.
1
Increasing the sample rate, without causing interrupt problems and keeping Simulink available for "on-the-fly" adjustments.
1