Bearing technology for dosing machines

The system with the designation "Autocap RT" is used in Dromont dispensing machines and has the function of automatically closing the dispensing head of the machines after each dispensing process. This protects the nozzles and the liquid remaining in them from drying out at the end of dispensing. The system then opens the head again automatically with the next dispensing command. Closure is achieved by the movement of a special cap equipped with a humidification system. This is placed under the nozzle area of the dispensing head to create a closed and humid environment. The contents are kept liquid while a seal is pressed around the edge of the head. This creates a suitable seal that prevents the dispersion of the moist atmosphere thus created.

The Dromont vending machines in which the system is used are used in a variety of areas:

• in shops and shopping centres open to the public (e.g. paint shops, Brico and various DIY stores)
• in industrial environments as stand-alone dosing devices
• in industrial environments as components of dosing systems

In all cases, the operating conditions are generally in an ambient temperature range of 15°C to 30°C and in a potentially dirty atmosphere that can easily contain fine dust, at least inside the machine.

Furthermore, the following challenges had to be overcome:

• vertical displacement and horizontal movement with a single drive
• Enabling the most effective and uniform sealing possible with the head closed
• Fast actuation (less than 1 second)
• very low actuating force
• easy adjustment during installation
• complete absence of maintenance work
• reliability over the entire service life of the machine (more than 10 years)
• small overall dimensions
• noiselessness
• low costs

The screw drive is the centrepiece of the system. The high reversibility, which is made possible by the high efficiency and lead angle of the dryspin® thread, made it possible to use a single actuator for the two engaging movements. This enables vertical release of the cap from the head and horizontal removal of the cap from the dispensing area. The threaded spindle and lead screw nut are actuated with vertical translation in order to achieve a joint vertical movement or a rotation of the spindle around its own axis, depending on the execution phase. The separation of the two phases of translation and rotation was achieved by a moving end made of iglidur® J, which is firmly connected to the dryspin® spindle. It is guided in a "L"-guidance, the vertical and horizontal sections of which only allow vertical translation or rotation of the dryspin® spindle. In this way, it was possible to achieve two completely different movements with a single, very simple linear drive, both in terms of type and torque.

The use of igus® components was essential in order to:

• allow actuation in two separate phases of translation-rotation with a single actuator, instead of having to resort to two separate actuators or a helical actuation, which would have led to various additional problems: cost, impediment to handling, need for lubrication, etc.
• to keep the required actuating force very low (less than 800 g), which allows the use of a very low power actuator with very small dimensions. This is crucial, as the system must be accommodated in the small space available inside the machine dome.
• the entire movement of the head closure carrier (cap) must be carried out with a very short actuation stroke: the total stroke of the linear actuator is 18 mm, of which 8 mm is used for the vertical displacement and 10 mm for the 45° rotation of the cap carrier
• to keep the overall dimensions of the entire system extremely compact
• achieve extremely fast actuation thanks to the extreme compactness of the system's kinematics (around 0.5 seconds for the entire opening-closing stroke)