The AS-i fieldbus helps a machine building team complete a
pneumatically driven, twelve-station assembly unit in just 16 weeks from
concept to commissioning - and cut labour costs into the bargain
Molecular Products manufactures special polypropylene canisters,
containing soda lime and two foam filters, which are used to filter
carbon dioxide from the breathing circuits of anaesthetic machines. A
recent upgrade at its manufacturing plant included the design and build
of a new machine to automate the assembly of this six-part component.
Molecular's partners in this project included machine builder, Werner
Engineering, ultrasonic welding specialist, Telsonic and pneumatics
supplier, SMC.
The whole project was completed in 16 intensive weeks, recalls Werner
director, David Norton, a time frame achieved, thanks to Molecular
Products' specification for a two-wire AS-i fieldbus system, which made
both economic and design sense in view of the system's high I/O count. In
addition to saving labour costs, the AS-i system gave the 12-station
machine an aesthetically pleasing look.
The first nine stations are dedicated to placing filter pads and
dispensing measured quantities of soda lime into the canisters. Because
of the corrosive nature of soda lime, hard anodised and stainless steel
is used extensively in the construction of this machine. At station 10,
lids are placed on the canisters and Telsonic's ultrasonic welding rig
goes to work welding the two together. The canisters are then pressure
tested to 2.5psi to check weld integrity, before proceeding to station 11
where transit covers are placed over the canister inlet and outlet. Any
canister failing the pressure test at station 10 (pressure decay of 10%
or less detected), is identified in the sequence and rejected once it
reaches the final station. The rate of production can be as high as ten
parts per minute, but this is reduced to six, if the pressure test is
included in the cycle.
The AS-i system networks 29 pneumatic actuators and an electric cam index
box, which drives the machine's main rotary table. SMC's Russell Lotinga
is convinced AS-i was the right choice for this project. It was a
challenge, but the two-wire system was the way to go, considering the
number of cylinders and sensors. We carried out a cost-saving exercise at
the beginning, comparing two-wire AS-i with a conventional system. With
the two-wire bus, the parts were slightly more expensive, but the labour
cost savings were tremendous.