Roller hold down device

A roller hold down device for removable work table which has a pair of rollers which extend transversely across the workpiece mounted on the movable table so as to hold it down and with a pair of cam roller members mounted on either side of the movable table and formed with cam portions so as to engage the rollers at the end of travel so as to force the rollers up away from the workpiece and also so as to prevent the rollers from falling off of the end of the workpiece. The rollers are controlled by hydraulic cylinders which can be actuated to automatically move them to the down position and also to move them to the up position.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates in general to movable work tables for a workpiece 
and in particular to a novel roller hold down apparatus. 
2. Description of the Prior Art 
Various clamps and other arrangements are known for holding workpieces to a 
work table. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a novel roller hold 
down device for holding a workpiece to a moving table wherein the rollers 
are rotatably supported at opposite ends by bearings which are connected 
to piston rods mounted in hydraulic cylinders which when actuated bias the 
rollers down against the workpiece to hold it on the moving table and 
wherein a pair of cam guide members are attached to the movable work table 
and are provided with cam portions such that adjacent the ends of movement 
of the movable table such cam portions engage the rollers to move them up 
away from the workpiece so as to prevent the rollers from falling off the 
end of the work table as the end of the work table passes under the 
roller. 
It is an object of the present invention to provide automatic roller hold 
down mechanism which holds a workpiece to a moving table but which 
releases the workpiece as the end of the table is approached by the roller 
.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 illustrates the novel roller hold down mechanism of the invention 
10. A base member 11 is formed with a pair of longitudinal supports 12 and 
13 upon which guide rails 14 and 16 are mounted. A movable work table 17 
is formed with rail engaging roller brackets 22 and 23 which engage rail 
16 and corresponding roller brackets 22a and 23a which engage the rail 14. 
The roller brackets 22 and 23 allow the work table 17 to move 
longitudinally on the rails 14 and 16 and such movement is facilitated 
with a motor 35 mounted on the frame 11 as illustrated in FIG. 3 and 
drives a shaft 31 mounted in bearings 36 and 37 at opposite ends of the 
frame 11. The shaft 31 is threaded between the bearings 36 and 37 and 
engages a threaded member attached to the lower surface of the work table 
17 so as to drive the work table 17 back and forth on the frame 11. 
A workpiece 18 may be mounted on the upper surface of the movable table 17 
by means including end clamps 37 and 38 which are formed with workpiece 
engaging lips 8 and 9, respectively which engage the upper surface of the 
workpiece 18. The clamps 37 and 38 are formed with slots 44 and 42 which 
extend in the vertical direction and bolts 43 and 41 extend through the 
slots and are attached to the work table 17. As is best illustrated in 
FIG. 2, the clamp 37 has a lower portion 6 which extends beneath the work 
table 17 and a cylinder 46 has a piston rod which is connected to the 
portion 6 so as to move the clamp 37 up and down so that the lip 9 engages 
the workpiece 18 and hold it to lock its end to the moving table 17. 
A pair of hold down rollers 61 and 62 are provided for also holding the 
workpiece 18 down to the work table 17 and the roller 61 has end portions 
63 and 64 at either end which extend into bearings 66 and 67 that are 
respectively mounted on piston rods 68 and 69 which are received in 
cylinders 53 and 50. The roller 62 has end portions 71 and 72 which extend 
into bearings 73 and 74 which are mounted on piston rods 76 and 77 which 
extend into cylinders 54 and 60. 
The cylinders 53 and 54, 50 and 60 are rigidly attached to the base 11 and, 
for example, the attachment of the cylinders 53 and 54 is illustrated in 
FIG. 1 where they are mounted to U-beams 51 and 52 which are attached to 
the base 11. It is to be realized that the cylinders 50 and 60 are also 
rigidly attached to the base 11. 
Side cam members 19 and 21 are attached to table 17 and are provided with 
relatively thick ends 82 and 93 which join a slanted cam portion 83 and 
92, respectively, and the opposite end is formed with higher portions 84 
and 90 which connect to the lower center portion 81 with a slanted surface 
86 and 91 as shown. The cam members 19 and 21 respectively engage the 
portions 63 and 71 of the rollers 61 and 62 and the portion 64 and 72 such 
that if in the condition when the rollers 61 and 62 are held down on the 
workpiece 18 due to the fact that the cylinders 53 and 50 and 54 and 60 
are actuated the cam portions 83 and 92 will force the roller 61 up away 
from the workpiece 18 when the roller 61 approaches the end 130 of the 
workpiece 18. This prevents the roller 61 from falling off of the end of 
the workpiece 18 and the table 17 thus blocking the movement of the work 
table in the opposite direction which could also damage the roller 61. It 
is to be realized that the higher portions 82 and 93, 84 and 90 are of a 
sufficient length that the rollers 61 and 62 will not run off the ends of 
these members. 
The movable table 17 may be associated with a routing machine such as a 
Powermatic Computer numerically control router such as illustrated in 
FIGS. 3 and 4. The router tool 103 is mounted on a movable holder 102 and 
the router tool is driven by a motor 105 which is mounted on a support 100 
which is in turn mounted on a vertical support member 101 which may be 
fixed relative to the base member 11. Thus, the router 103 can be moved in 
the transverse direction relative to the workpiece 18 so that the router 
103 may cut a groove 150 as illustrated in any desired pattern as the work 
table and workpiece are moved to the left and right relative to FIGS. 3 
and 4. 
FIG. 5 illustrates a control system for the novel hold down system of the 
invention wherein a control 113 has a multiple cable 114 with a first 
cable 114a connected to a solenoid valve 110 which is connected to control 
the positions of the piston rod 68 and 69 by energizing the cylinders 53 
and 50 with a suitable hydraulic supply from a pump 220 which is connected 
to valve 110 by a suitable supply line 221. A lead 114b is connected to a 
solenoid valve 111 which is connected to control the cylinders 54 and 60 
so as to move the piston rods 76 and 77 associated with the roller 62. A 
solenoid valve 112 is connected by electrical lead 114c to the control 113 
and controls the position of the piston rods associated with the hydraulic 
cylinders 46 and 47 which actuate the hold down clamps 37 and 38. 
In operation, the solenoid valves 110, 111 and 112 are moved to the 
positions to raise the roller 61, 62 to the up position as illustrated in 
dash line in FIG. 4. The clamps 37 and 38 also move to the up position so 
that a workpiece 18 can be mounted on the work table 17. After the 
workpiece is mounted on the work table the solenoid valves 110, 111 and 
112 are energized so as to move the clamps 37 and 38 to the down position 
to lock the end of the workpiece 118 to the table 117 and to move the 
rollers 61 and 62 to the down position so that they engage the upper 
surface of the workpiece 18 at spaced positions as illustrated in FIGS. 1, 
2, 3 and 4. Then the motor 35 is energized to move the workpiece 18 and 
the work table 17 relative to the router 103 and the router 103 cuts a 
suitable groove 150 in the workpiece. If the table 17 and workpiece 18 
move until the cam portions 83 and 92 engage the portions 63 and 64 of the 
roller the cam portions will move the roller 61 up away from the surface 
of the workpiece 18 and the portions 82 and 93 will hold the roller out of 
engagement with the workpiece 18. In a similar manner, if the work table 
17 and workpiece 18 is moved to the right relative to FIGS. 1, 3 and 4 
such that the cam portions 86 and 91 engage the portions 71 and 72 of the 
roller 62 the roller 62 will be cammed upwardly so that it rolls on the 
portions 84 and 90 thus disengaging the workpiece 118 and preventing the 
rollers 62 from falling off the end of the table 17. 
Thus the present invention provides a positive mechanical release of the 
rollers 61 and 62 as they reach the ends of the workpiece. Also, the 
computer for the router may be connected to control the rollers 61, 62 and 
the clamps 37 and 38 to automatically release them. 
The novel roller hold down system of the invention comprises a clamping 
technique used to securely hold sheet materials for driling, boring, 
sawing, routing and shaping on a movable table of a machine tool. Warped, 
cracked, rough and porous materials cannot be practically held with a 
vacuum system. Also, good quality materials may be cut into small parts or 
part configurations which are not suitable to be held with a vacuum. The 
roller hold down apparatus of the invention holds sheet material flat 
against the moving table while moving under the cutter head as the cutter 
head machines the workpiece as it passes between the rollers. The clamps 
37 and 38 secure the workpiece 18 flush against the end of the table 17 
and these clamps have to inhibit motion of the workpiece in the vicinity 
of the cutting zone. 
As the rollers approach the end of the table travel the outside roller is 
raised either mechanically by the roller cams or electronically by the 
computer controlling the router. This action prevents the roller from 
falling off the table and then being damaged as the table moves back 
against the outside roller. 
Although the invention has been described with respect to preferred 
embodiments, it is not to be so limited as changes and modifications can 
be made which are within the full intended scope of the invention as 
defined by the appended claims.