Compound tool drive

A machine for placing surface mount electronic components has a tool holder that is vertically displaceable and rotatable to pick-up and deposit components. The tool holder can be conjointly axially advanced and rotated to improve the productivity of the system.

The present invention relates to machines for placing electronic surface 
mount components on a printed circuit board. 
Conventionally, surface mount components are picked up by vertically 
lowering (Z motion) a tool head holding a vacuum tool into engagement with 
a component at a feed location. The tool head is then elevated and 
rotationally oriented (theta motion) to properly orient the component and 
then vertically downwardly lowered to place the oriented component on the 
circuit board. The tool head and printed circuit board are relatively 
displaced horizontally (X,Y) to locate the tool over the location on the 
circuit board which is to receive the component. Such Z and theta motions 
are conventionally completed sequentially. 
It is an object of the present invention to provide a improved tool head 
drive where Z and theta motions can be completed simultaneously. This will 
increase the productivity of the machine. 
Other objects and advantages of the present invention will become apparent 
from the following portion of this specification and from the accompanying 
drawings which illustrate in accordance with the mandate of the patent 
statutes a presently preferred embodiment incorporating the principles of 
the invention.

A tool head 10 which has a tool 12 for engaging and holding a surface mount 
component 14 to be placed on a printed circuit board 15 is secured to a 
ball spline drive shaft 16. A pair of ball spline nuts 18 are located in 
spaced relation within the central bore 20 of the spline nut housing 21 
and a pair of keys 22 lock the ball spline nuts 18 to the spline nut 
housing 21. A ball spline nut 18 has pockets 23 which hold steel balls 25 
which ride along axial slots 27 defined in the ball spline shafts 16 (only 
one enlarged pocket slot is shown for purposes of clarity. Further details 
of a ball spline unit are disclosed in U.S. Pat. No. 4,799,803. A pair of 
spaced radial bearings 24 which are supported by the theta housing 26, 
rotatably support the spline nut housing 21 and are preloaded by 
compressively locating a wave spring washer 28 between the upper radial 
bearing and the theta timing belt pulley 30 which has a central threaded 
bore 32 threadedly received by the threaded end 34 of the spline nut 
housing 21. When the theta stepping motor 36 (FIG. 2) is driven, the 
timing belt 38 is driven to rotate the pulley 30 and hence the tool head 
about the axis of the ball spline 16 (theta motion). 
A clamp 50 which is secured to the Z axis timing belt 52 supports a radial 
bearing 53 which receives a reduced diameter portion 54 adjacent the 
threaded end 56 of the ball spline. A suitable nut 58 secures the ball 
spline to the radial bearing. The Z axis timing belt 52 is supported 
between spaced pulleys 60 and is tensioned by an idler shaft 62. A second 
stepping motor 70 secured to the Z axis housing rotatively drives the 
upper pulley so that Z axis motion may take place conjointly with theta 
motion.