My
submission relates to the work I have done on a prototype designed to reduce
changeover time on production lines for currently manually adjusted
equipment. The prototype is a box
folding machine fitted with linear actuators or electronic rams which transmit
position information to a microcontroller which controls their motion.
What
is the nature of the company's business? (marketplace, products, size)
Pera
is an engineering consultancy firm, working on projects for single companies
(single client projects) or projects funded by the EC in partnership with a
number of companies (collaborative projects).
Pera also has a lot of experience working with other businesses
improving business processes and providing groundbreaking technological
solutions.
The
prototype will be used to illustrate the reduction in time and manpower for
changeovers, and hopefully encourage relevant companies to have frequently adjusted
equipment converted to free up engineers for other work and improve
output. The outcomes would include a
reduced downtime and additional flexibility in batch production.
The
box folding machine was constructed with linear actuators instead of a
nut-and-bolt method of changing settings.
Linear actuators work by a motor attached to a spindle which moves a ram
forwards or backwards depending on the polarity. A resistor is incorporated which changes in resistance as the ram
moves out, and by putting a voltage across this it is possible to determine the
position to a high degree of accuracy.
The simplest method of control we decided would be to use a programmable
microcontroller, and a type of circuit known as an H-bridge which provides
power to the motors based on logical input signals. These are common circuits and are produced in microchip form. I drew up a circuit diagram of the motor
controller circuit including a few other components to ensure correct
operation. The prototype incorporates
four actuators, so I produced a plan and mounted four motor control circuits on
stripboard (a plastic grid with holes for components to be mounted easily, and
parallel strips of copper to connect individual lines of holes). We used a transformer to convert mains
electricity to 24v DC. The
microcontroller provides logic signals of 5v to trigger the motor controller
circuits which then channel 24v to the actuators. The microcontroller contains a program which accepts controls
from a computer via a serial cable and moves all four actuators the correct
distance simultaneously. Fine tuning is
accomplished by 'nudge' functions which move individual actuators forward or
backward by a fraction of a millimetre.
The
main challenge was the current limit of the H-bridge chips. Each chip includes two H-bridges, and so, in
theory, can control two motors, but the actuators draw a higher current than
the H-bridge chips can cope with, so the controller circuits had to be
paralleled up. By controlling only one
actuator from each chip, the current rating of the chips is doubled. Unfortunately, even this was inadequate for
when the motors were drawing full power, and two chips burnt out during initial
testing. The testing also showed that
the actuators were too fast for accurate positioning by the program. Both problems were overcome by rerouting the
power supply to the motor control circuits through resistors which would both
reduce the current through the chips and slow the actuators down. Fuses were also added to be doubly sure the
circuit would be protected in the event of a short.
This
prototype has been developed for display at relevant conferences. It will be available for many companies to
see, and, if the idea is taken on by companies with a lot of production line
work, it could save a lot of money. In
the food industry especially, changeover time is becoming a larger proportion
of downtime as batch sizes become smaller and flexibility is key to success. The simplicity of the design from the
operator's point of view means it can be employed by people with minimal
training and at lower risk than previously.
Batch sizes currently mean that equipment is used at one setting for an
hour and then brought out of action for 10 minutes to prepare for the next
batch. Compared to this our prototype
will reduce changeover time by at least 90% with proportional cost and manpower
savings as well as added flexibility.
The
nature of the work has necessitated a better understanding of electronics and
computer programming. It has improved
my skills in planning as well as electrical circuit and system assembly.
The
rig was designed and built to illustrate the rapid changeover concept some
years ago, but the control method was more complex. Our prototype provides an easy-to-use, desk-mounted demonstration
piece.
____________________________________________________________________
Tony
Clohesy
Manager’s Statement
I can
confirm that Tony's submission for this competition is true and a factual
record of work that he has undertaken recently.
The
box folding prototype has been constructed for a client who wishes to
demonstrate the SMED (Single Minute Exchange of Dies) principle within the food
processing and packaging industry. Tony
has been responsible for the design and construction and testing of the
prototype. This work has included the
design, build and test of several electronic circuits, construction of the
prototype and programming the control system.
The
project has not been straightforward as changes have been made to the
specification during the completion.
Tony has coped with these changes well and has shown that he is able to
think on his feet and implement changes in the prototype quickly and
effectively.
The
final prototype will be sold to our client.
The success in completed delivery of the prototype will be directly due
to Tony's effort. This effort will
provide a healthy revenue and help us to generate further income from this
client.
Tony
has worked on other projects of a similar nature and has always delivered
successful solutions in the required timeframe. Sometimes this has involved additional work at short notice in
order to meet deadlines. Tony has always risen to the challenge. His work is thorough and well
documented. This is a great help to the
rest of the team.
Ben
Palethorpe