Lifter for a Screen Printing Machine
Publication Date: 2004-Feb-19
The IP.com Prior Art Database
A lifting mechanism for a rotary screen printing machine which has a stationary frame for the print heads and a rotatable frame for the pallet arms. The lifting mechanism incorporates two ball screws to lift the rotatable frame for the pallet arms. ©
Rotary Screen printing machines are used for screen printing of garments and utilise a plurality of fixed print heads beneath which are positioned a plurality of garment support pallets which are moveable from one print head to the next. The pallet arms radiate out from a central column which forms a rotor that rotates the pallets from one printhead to the next in a serial indexing fashion. The pallet arms are raised toward the printheads for the printing operation and are lowered for rotation to the next print head.
USA patent 4934263 discloses a screen printer of this type where pneumatic cylinders are used to drive the rotation and lift the rotatable column.
USA 4974507 discloses a screen printing machine in which the rotatable column incorporates an air bag counter balance to the weight of the rotatable column when it is being lifted or lowered by a pneumatic cylinder.
USA patent 5913264 discloses a series of hydraulic cylinders to lift the rotor relative to the stator which supports the print heads.
USA patent 6408751 discloses a screen printer in which the lifting is achieved using a single ball screw mechanism driven by an electric motor and a counter balance provided by an axially extending compression spring which is coaxialwith the axis of the ball screw. The disadvantage of this arrangement is that it clutters the central column which is needed for other drive and control functions of the machine. Placing the lifting mechanism on the central axis does not address the cantilever effect of the extended arms.
A simple and robust lifting mechanism for screen printing machines.
comprises a rotary screen printing machine which includes
a) a stationary frame supporting a plurality of print heads
b) a rotatable frame supporting a plurality of pallet support arms
c) a base for said rotatable frame supported by at least two evenly spaced screw threaded shafts.
By using two or more lifting screws the lifting apparatus is removed from the central column of the rotary machine thus reducing the number of mechanisms which use that column. By spacing the lifting screw away from the central axis and by using two or more screws the weight borne by each lifting screw is greatly reduced and the cantilever effect of the extended pallet arms is reduced.
The screw threaded shafts may be ball screws driven by a common drive means preferably a servo motor or a stepper motor. The two ball screws may be connected by a belt to the drive motor or alternatively on of the ball screws may be have two belt pulleys one for a belt from the drive motor and one for a belt to the second ball screw. In another embodiment one ball screw may be directly driven by the drive motor and the second ball screw driven by a belt from the first ball screw. This arrangement allows the rotatable frame to be raised to any height intermediate the height of the fixed print arms and the lowest or initial position of the pallet arms.
The weight of th...