On-off traditional pneumatic drives are most widely used in industry offering
low-cost, simple but flexible mechanical operation and relatively high power to
weight ratio. For a period of decade from mid 1980's to 1990's, some initiatives
were made to develop servo pneumatic drives for most sophisticated
applications, employing purpose-designed control valves for pneumatic drives
and low friction cylinders. However, it is found that the high cost and complex
installation have discouraged the manufacturer from applying servo pneumatic
drives to industrial usage, making them less favourable in comparison to their
electric counterpart. This research aims to develop low-cost servo pneumatic
drives which are capable of point-to-point positioning tasks, suitable for
applications requiring intermediate performance characteristics. In achieving
this objective, a strategy that involves the use of traditional on-off valve, simple
control algorithm and distributed field-bus control networks has been adopted,
namely, the design and control of Components-based Integrated Pneumatic
Drives (CIPDs).
Firstly, a new pneumatic actuator servo motion control strategy has been
developed. With the new motion control strategy, the processes of positioning a
payload can be achieved by opening the control valve only once. Hence, lowspeed
on-off pneumatic control valves can be employed in keeping the cost low,
a key attraction for employing pneumatic drives. The new servo motion control
strategy also provides a way of controlling the load motion speed mechanically.
Meanwhile, a new PD-based three-state closed-loop control algorithm also has
been developed for the new control scheme. This control algorithm provides a
way of adapting traditional PID (Proportional Integral Derivative) control
theories for regulating pneumatic drives. Moreover, a deceleration control
strategy has been developed so that both high-speed and accurate positioning
control can be realised with low cost pneumatic drives. Secondly, the effects of system parameters on the transient response are studied. In assisting the analysis, a second order model is developed to encapsulate the velocity response characteristics of pneumatic drives to a step input signal. Stability
analyses for both open loop and closed-loop control have also been carried out
for the CIPDs with the newly developed motion control strategy. Thirdly, a
distributed control strategy employing Lon Works has been devised and
implemented, offering desirable attributes, high re-configurability, low cost and
easy in installation and maintenance, etc to keep with the traditional strength for
using pneumatic drives. By applying this technology, the CIPDs become
standard components in "real" and "virtual" design environments. A remote
service strategy for CIPDs using TCP/IP communication protocol has also been
developed.
Subsequently a range of experimental verifications has been carried out in the
research. The experimental study of high-speed motion control indicates that the
deceleration control strategy developed in the research can be an effective
method in improving the behaviour of high speed CIPDs. The verification of
open loop system behaviour of CIPDs shows that the model derived is largely
indicative of the likely behaviour for the system considered, and the steady state
velocity can be estimated using the Velocity Gain Kv. The evaluation made on a
pneumatically driven pick-and-place machine has also confirmed that the
system setup, including wiring, tuning, and system reconfiguration can be
achieved in relative ease. This pilot study reveals the potential for employing
CIPDs in building highly flexible cost effective manufacturing machines. It can
thus be concluded that this research has developed successfully a new
dimension and knowledge in both theoretical and practical terms in building
low-cost servo pneumatic drives, which are capable of point-to-point
positioning through employing traditional on-off pneumatic valves and
actuators and through their integration with distributed control technology
(LonWorks) by adopting a component-based design paradigm