Delft University of Technology
Faculty Mechanical, Maritime and Materials Engineering Transport Technology
T.A. van Vianen Design of an Interface between punch and packaging machines Masters thesis, Report 2005.TL.6924, Transport Engineering and Logistics.
Reason of the research
EBM Techniek is a great player worldwide in producing cotton pads. The market is served with two machines. One machine produces high volumes (75 bags/minute) with restricted different pad types (High Capacity Machine) and the other machine produces a lower volume (42 bags/minute) but is more flexible to changeover to other pad type (Flexible production machine). Both machines punch the pads out of cotton fleece, using the same punching principle. The transport- and packaging part differs for both machines, but both machines pack the pads into the same type of plastic bags.
Figure 1: Consumer price development
Nowadays, the sales market of cotton pads is a matured market and suppliers are defining their medium range planning. Figure 1 shows the decrease of the consumer price of the cotton pads. The cost price reduction of the standard pad (Ø57) results that some suppliers focus on reducing the cost price and others focus on exclusive product quality. These suppliers have to develop new product- and packaging types to fulfill the consumer's demand.
Recently, new feminine hygienic products have been developed. The second figure shows plastic bags, filled by EBM machines. The other pictures show new developed hygienic products. The jar and foil can be bought already, but the material of these pads is a kind of plastic fibre in stead of cotton. The following advantages of cotton will probably offer sales possibilities. Cotton feels natural to the skin, is relatively cheap and has high absorption ability. The cotton pads in the jars and foil must be pre-moistened with eye make-up remover, nail lacquer remover or facial cleaning and eventually individual packaged to use in operation-rooms.
Figure 2: Plastic bags (left); Jar (middle left); Travel box (middle right); Foil (in box) (right)
To fulfill the new consumer's demands, EBM needs to improve their machines. Some suppliers need a machine, which is more flexible. The new machine must be able to produce smaller batches, according consumer's demands.
To accommodate the market shifting optimally, EBM needs to improve its machines. EBM considers the optimal direction to maintain the punching principle and accomplish the packaging of pads with a modular system. A new interface must connect the punch and the several packaging machines.
The title of the research is 'Design of an Interface between punch and packaging machinesö. The principal of this research is EBM Techniek represented by Ir. M. van Putten.
Execution of research
To define the requirements of the new interface, both EBM machines are analyzed.
Customers experience the prices of both existing EBM machines fairly high. For producing the final products, packed pads, the machine needs a punch and packaging machine. Transport between both machines is an additional function, but the cost price of this interconnecting part contributes in the total cost price. The intention of the new interface is a cost price reduction while capacity remains unaltered. The transport part of the high capacity machine has a cost price of €189,700 and the transport part of the flexible-production machine has a cost price of €158,000.
When punching pads out of fleece, a lot of cotton fluff is formed. This fluff can be easily caught between the rotating- and translating parts. The critical parts, linear motion guides and the sleeve bearings of the main shaft, must be blown off with compressed air before each product shift to prevent an accumulation of cotton fluff. Due to this fluff, the critical parts must be lubricated each week. Once a year, both existing machines need an elaborate service to replace these parts.
To define the disturbances of both existing machines, operational data is analyzed. This analysis shows that photoelectric switches often troubled because of the accumulation of cotton fluff on the emitter. Vertical bag packaging is preferred because this causes fewer disturbances than horizontal bag
packaging. Another remarkable aspect is the relation of the control complexity (sensors, switches, pneumatic valves and electric motors) divided per main function and the number of disturbances for this function, see figure 3. In addition, the number of control components relates to the availability of the machine due to disturbances.
Figure 3: Relation control complexity and disturbances
Due to maintenance and disturbances the total operating availability of the high capacity machine is 82.2% and for the flexible-production machine 92.4%. The flexible-production machine is designed four years ago with the operational experiences of the high capacity machine, which is designed almost twenty years ago.
The technical and economical knowledge of both EBM machines together with the suppliers demands, result in requirements of the new interface. Three new concepts and both existing transport parts are analyzed of their fulfillment of the most important requirements. The robot concept achieves the highest value (0.82).
Figure 4: Interface with robot
A robot positions the robot-gripper, for multi-stacks, above the punch. Bags are already placed at the spoons of the robot-gripper. At the end of the punch cycle, when a stack of pads is present in the stamp-buffer, the pusher-pipes of the punch move the stacks into the robot-gripper. When packaging stacks into plastic bags, the robot positions the robot-gripper under the rejecting pipes of the seal-unit. The bags with pads are pushed off the spoons and the plastic bags are sealed. The robot transports the robot-gripper to the bag-place unit, where on the empty spoons a bag is placed. If the (pre-moistened) pads are packed into jars or in foil, the robot positions a different robot-gripper above the dead-plate or on the supply belt of the flow-wrapper.
The robot with dedicated robot-gripper concept is relatively cheap and the robot has the highest level of flexibility. The main advantage of the robot is that no other transport equipment is needed for bag packaging. If other packaging machines are required in future, the robot is also able to transport stacks to the new packaging machines.
The Flex punch will be probably more used because of the changeover flexibility to other pad- or packaging type. In a starting sales market, flexibility is more important than high capacity.
The dedicated robot-gripper must have the following functions: spread the carriers or positive grippers to achieve the required pitch of the packaging machine, separate both rows to prevent a collision with the environment and close the spoons before placing into the opened bags.
Figure 5: Robot-gripper above punch (left); in-seal and bag-place unit (middle); with positive grippers (right)
Figure 5 shows a possible solution for the robot-gripper. The first picture shows the robot-gripper above the punch, with upward directed spoons of the carriers. The pads are moved upwards in the carriers by the pusher-pipes of the punch. The second picture shows the robot-gripper 180° rotated under the rejecting pipes of the seal-unit or above the bag-place unit. The third picture shows the robot-gripper equipped with positive grippers. The positive grippers are used to transport (pre-moistened) stacks from the punch to jar- or foil-packaging machines.
packaging pads into jars or foil. The total operating efficiency of the new machine is 93.6%, this value is higher than both existing machine. The control complexity of the new machine is reduced and the robot with robot-gripper is expected to have less maintenance.
The new machine with the Flex punch and bag-packaging machine costs €480,000. The development costs of the first machine are approximately €66,500. The new interface has a cost price of approximately €109,000. This is a reduction of €50,000 in comparison of the transport part of the flexible-production machine. Robot movements replace transport actions in the vertical bag-packaging machine, which results in a cost price reduction of the packaging machine of more than €40,000. The price per bag due to depreciation of the new machine equipped with bag packaging is €0.011 in stead of the €0,014 and €0.016 of both existing machines.
Conclusion
It is possible to simplify the cotton pad-producing machine, at the same time improve the flexibility to several types of pads, and new packaging types. The robot-gripper needs to be developed in details.
Recommendations
Investigate pre-moistening of the pads before building a stack. Possibly, spraying nozzles can be placed in the pusher-pipes of the punch or in the stamp-buffer.
Investigate if the joints of the robot contaminate with cotton fluff by placing an operating robot in a customer's factory. Elaborate also the crank and rocker drive (=concept 3) for pack the stacks only in jars or foil.
Investigate the possibility to use two robots with the HCM punch to achieve an alternative high capacity layout. Investigate the cost price reduction of the Flex punch (hydraulic driven punch?)
Reports on Transport Engineering and Logistics (in Dutch)
