Printing – Stenciling – Multicolor
Patent
1989-04-10
1990-06-19
Crowder, Clifford D.
Printing
Stenciling
Multicolor
1983452, F16H 1904, F16H 2702, B23Q 1606, B41F 1514
Patent
active
049342630
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a rotary indexing mechanism which is particularly suitable for use with carousel devices such as screen printing carousels.
Screen printing carousels typically comprise a multiple armed fixed frame and a matching multiple armed movable frame mounted to rotate above or below the fixed frame. The print heads may be fixed and the screen platens movable or vice versa. It is particularly desirable that each indexed motion of the rotary frame come to a smooth stop substantially free of jarring and vibration. This objective can be theoretically met by suitably programmed control of an electric motor drive or linear motor system but it would be preferable to be able to employ a much less expensive and less complex hydraulic or pneumatic actuator. However, traditional rotary indexing mechanisms suitable for rams, e.g. crank based arrangements, are difficult to control to the extent desired.
Another problem of screen printing carousels of this type is owing to the potential danger to the operator resulting from the multiple armed movable frame. If the operator was within the sweep of these arms when they are operating there is a possibility that serious injury could be caused as result of the operator being struck by a moving arm.
It is accordingly an object of the invention in accordance with one aspect to provide a rotary indexing mechanism in which each indexed motion is brought to a smooth stop.
It is an object of the present invention in accordance with another aspect to provide an arrangement whereby the possibility of injury to an operator as a result of the moving arms is reduced.
According to one aspect of the present invention there is provided a rotary indexing mechanism for a screen printing machine, the machine comprising a carousel which includes a multiple armed fixed frame and a complementing multiple armed movable frame mounted to rotate above or below the fixed framed, a plurality of print heads mounted to one of either of the fixed frame or the movable frame and a plurality of screen platens mounted to the other of either the fixed frame or the movable frame the rotary indexing mechanism comprising a coupling member mounted for reciprocatory rotary motion, and including engagement means operable to engage the movable frame during a selected portion of said reciprocatory rotary motion, drive means which includes a linear actuator for effecting said reciprocatory rotary motion a transmission mechanism operatively connecting said drive means to said coupling member and, fluid damper means mounted so as to oppose said reciprocatory rotary motion of said coupling member at least in a terminal section of said selected portion of the motion in such a manner as to slow said motion to a smooth stop, characterized in that said transmission mechanism comprises a first linear rack operatively connected to said drive means, and pinion means engageable by said first rack said pinion means being operatively connected to said coupling member to cause said reciprocatory motion said transmission mechanism further including a second rack which is engageable with said pinion means and is operatively engageable with said fluid damper means said racks and pinion means being arranged so as to reduce or eliminate backlash.
In one form the pinion means comprises a first pinion which is adapted to engage with the first linear rack and a second pinion which is adapted to engage with the second linear rack the first and second pinions being mounted on a shaft which is common to both pinions.
In another form the pinion means comprises a single pinion mounted on a shaft with the first and second linear racks being adapted to engage that single pinion. Preferably the shaft extends generally parallel to the axis of rotation of the coupling member.
The transmission mechanism may comprise a crank which is rotatable by the drive means the crank including a pin receivable within a slot in the coupling member so as to be slidable therealong as the crank is rotated. The arrangement is such that the torque tra
REFERENCES:
patent: 4099460 (1978-07-01), Bubley et al.
patent: 4669378 (1987-06-01), Lee
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