This chapter deals with coil winders and calenders processing electrically nonconductive materials. The expression “coil winders” here can also mean paper winders. Unfortunately, the great masses and high speeds of these machines mid-action prevent stopping them before someone gets hurt. For paper winders capacitive sensors may only prove useful during the startup operation. Later on, other means have to be used to keep people out of danger. The startup phase is the time when manual interaction is needed most.
I always try to find the cheapest possible solution. I do not try to use the technology of capacitive sensors by all means. However, optical barriers can rarely be used with coil winders, because the foils deflect/mirror the light. This occurs mainly during startup. Again, this is the time when the sensors are needed most.
Capacitive sensors placed behind the processed material allow the construction of such machines or facilities at lower costs. The operability of the machines improves as well. In contrast to roller mills shielding electrodes can be used. Therefore the sensitivity and the operating distance are improved. A hand is now safely detected if placed in the vicinity of the inrunning nips of the rollers. Up to now, these machines are constructed with fences to keep people out of the dangerous zones. They are unnecessarily voluminous and expensive. With safe capacitive sensors the operator would be better protected during startup operation, too.
The annual production figures for coil winders and calenders are much higher than for roller mills. Most of the machines only process nonconductive materials. Plastic foils are wound or rewound, they are printed, laminated or processed otherwise. Calenders are frequently used to equal the thickness of foils. So, producing capacitive sensors for coil winders and calenders is economically very attractive.