Hydraulic position control for mechanical power press slides

A mechanically driven power press has vertical slide mechanism adapted to engage and reciprocate the upper movable element of a die set. Means for adjusting the shut height of said slide including a cylinder secured to said slide and a piston slidable therein and having threaded connection with a portion of said cylinder for shut height adjustment. An hydraulic chamber operable to effect working strokes of said slide. The shut height adjustment has a second threaded portion whereby when said first cylinder is pressurized the threaded parts in engagement with the threaded portion of the piston are forced apart to eliminate thread clearance and lock the shut height adjustment.

BACKGROUND OF THE INVENTION 
This invention relates to mechanical power presses for stamping sheet 
material and the like and more particularly to the type of power press 
known in the art as a mechanical press wherein the frame of the press has 
a base portion for receiving sheet metal stamping or forming dies and the 
crown of the press has eccentric or crankshaft means for driving a 
vertically reciprocal slide toward and away from the bed of the press to 
effect pressing strokes. The slide is supported and guided for such 
reciprocation by the frame of the press. 
Mechanical presses of this type are well known and it is likewise known to 
provide in conjunction with the vertically reciprocable slide of the press 
hydraulic overload features which are arranged to shut the press down when 
predetermined pressing forces are exceeded. This has been accomplished in 
the prior art by interposing hydraulic means in the slide of the press in 
such a way that when a given determined hydraulic pressure force is 
exceeded, the hydraulic protective valves open and operate means for 
shutting the press down until the malfunction causing the excessive 
pressing force is corrected. A typical hydraulic means for providing such 
an overload arrangement is shown in Spanke U.S. Pat. No. 4,166,415 
although this general hydraulic overload system has been known and used 
for many years. 
It is also known to provide hydraulic means operable to raise the slide of 
the press independently of the mechanical drive thereof in order to expose 
the die on the bed of the press for adjustment or other servicing. 
It is known in the prior art of mechanical presses to provide hydraulic 
means in conjunction with the crown of the press for raising the same to 
raise the slide of the press and thus expose the die on the bed of the 
press for purposes similar to herein contemplated. However, use of the 
hydraulic means in conjunction with the crown of the press is limited to 
this stated purpose. Examples of die inspection arrangements of this type 
are shown in Wrona U.S. Pat. No. 3,400,625 and Wrona U.S. Pat. No. 
3,662,640. The present invention contemplates self-contained means means 
acting between the mechanical connection or pitman of the press and the 
slide of the press in effecting all three of the above stated purposes. 
SUMMARY OF THE INVENTION 
The principal of the present invention is to provide a mechanical press 
with an hydraulic arrangement which provides an overload safety device in 
combination with means for hydraulically raising the slide of the press to 
expose the die member on the bed of the press without disturbing the shut 
height adjustment of the slide and also in combination with hydraulic 
means for locking the threaded connection between the pitman or connection 
which drives the slide of the press in vertical strokes and the connection 
thereof with the slide of the press. 
Reference will now be had to the hydraulic arrangement provided in the 
present embodiment of the invention which cooperates with the mechanical 
drive of the press to provide an overload prevention arrangement. Combined 
with the hydraulic overload arrangement are means for eliminating thread 
clearance in the vertical adjustment of the slide. 
An important novel feature of the present invention is the provision of an 
hydraulic arrangement which provides convenient means for raising the 
slide to give access to the die for servicing or removal of the die 
without disturbing the shut height adjustment of the slide of the press. A 
relatively simple air driven hydraulic system is provided for 
accomplishing all three of the above stated objects.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT 
The drawing shows schematically a power press driven mechanically by a 
conventional eccentric shaft 9 having a pair of eccentrics 10 and a pair 
of connections 11 which in the illustrated instance are pivoted at their 
lower ends to a pair of cylindrical head portions 12 of adjusting screws 
13. The numeral 14 designates portions of a slide which is guided for 
vertical movement in the framework 15 of the press for movement toward and 
away from the usual press bed 20 which is fixed to the press framework 15. 
In the interests of simplicity the drawing shows only the portions of the 
press mechanism which are concerned with the present invention and it is 
to be understood that the remainder of the press structure is entirely 
conventional in mechanical double crank presses and the principles of the 
invention are equally applicable to single crank or other mechanically 
driven presses. 
Referring particularly to the right-hand driving connection of the present 
embodiment, a hollow cylindrical member 16 known in the art as a barrel is 
fixed to the slide 14 at its lower end and has an upper end portion 17 of 
reduced diameter in which the head portion 12 of adjusting screw 13 bears 
for relative sliding movement. 
A worm wheel 18 has a lower flange portion 19 which is engaged between 
slide 14 and barrel 16 so that the worm wheel is fixed against axial 
movement relative to the slide 14 and is rotated by a worm journaled in 
the barrels 16 and engaging both of the worm wheels 18 of the two driving 
components. 
Referring to the right-hand driving connection, a hollow cylindrical member 
24 serves as a hydraulic withdrawal and overload piston and is internally 
threaded to engage the threads of adjusting screw 13. The upper end of 
member 24 abuts the interior ledge of barrel 16 which occurs at the lower 
end of reduced portion 17 of barrel 16. 
A sleeve member 26 serves as a locking nut. The upper end portion of sleeve 
member 26 is internally threaded to engage the threads of adjusting screw 
13. The sleeve member 26 is keyed to worm wheel 18 as at 27 and is keyed 
to the piston 24 as at 28 so that the piston 24 rotates jointly with worm 
wheel 18. 
Further reference will be had later herein to the details of operation of 
the connection adjusting screw and the hydraulic functions performed in 
connection therewith by the novel hydraulic arrangement herein provided. 
In the drawing, the numeral 30 designates a conventional air pressure 
regulator which controls the pressure of admission of operating air to the 
system from air supply 31. The degree of air pressure is indicated by a 
pressure gauge 33. In the drawing, the numeral 34 designates a two-way, 
normally closed, solenoid operated air valve. The solenoid, therefore, 
must be energized to activate the air system and in the drawing the 
solenoid is de-energized so that air pressure from conduit 35 does not 
enter the system. 
The constant air pressure arrangement thus provided supplies hydraulic 
pressure for operating the present system by means of a Haskel oil pump 37 
wherein the regulated air pressure from the line 35 operates to drive an 
oil pump 38, the air discharging by way of an exhaust 39. The flow of 
hydraulic fluid under the impetus of the pump is from right to left as 
viewed in the drawing and the hydraulic fluid to the pump 38 is supplied 
from a reservoir 40 of a valve assembly 41 which will be described in 
greater detail further herein. Hydraulic flow from reservoir 40 to pump 38 
is by way of a conduit 42. 
The output hydraulic pressure from pump 38 is by way of a conduit 44 which 
leads to an inlet passage of a four-way solenoid operated hydraulic valve 
designated 45 in the drawing. 
It will be noted from the right-hand barrel assembly in the drawing that an 
annular space 46 between worm wheel 18 and the hollow cylindrical 
hydraulic withdrawal and overload piston 24 is connected to the source of 
hydraulic operating pressure by way of a conduit 47. A second cylindrical 
hydraulic chamber 50 is provided between an outwardly projecting radial 
face of overload piston 24 and a downwardly facing radial formation of 
cylindrical member 16 (the barrel member). This hydraulic space is 
connected to the source of hydraulic pressure by way of a conduit 48 
leading from the four-way solenoid valve 45. 
The valve assembly 41 is provided to cooperate with the annular chambers 46 
of the barrel assemblies of the press to provide overload means for 
stopping the operation of the press when the hydraulic pressure in chamber 
46 exceeds a pre-determined amount which amount is calculated as the 
maximum tolerable load limit. The pressure developed in the overload 
chambers 46 is transmitted to a passage 54 of overload valve 41 by means 
of an extension from conduit 47 designated 51 in the drawing. A ball check 
valve 52 is normally held seated against hydraulic flow from conduit 51 by 
air pressure from conduit 35 which acts against a piston 53. 
When the tolerable pressure in chambers 46 is exceeded the hydraulic 
pressure from conduit 51 unseats the ball valve 52 which raises piston 53 
and thus trips an overload limit switch 55 and this deactivates the system 
by cutting off the air supply through solenoid valve 34 which switches the 
solenoid valve 45 to the illustrated position which allows oil to flow to 
the reservoir 40 of the overload valve and thus shuts down the press. 
In the drawing the numeral 56 designates an hydraulically operated pressure 
switch which will permit press operation only when the hydraulic system 
pressure has reached the switch setting. 
Referring now to the general operational procedure of the foregoing 
structure, the four-way solenoid valve 45 which is shown in the 
de-energized position in the drawing, must be energized to allow oil to 
flow from the pump 38 through ports P and A of valve 45 to thus fill the 
lower cavity 46 of the barrel 16. At this time oil is forced out of the 
upper cavity 50 through ports B and T and returned to the reservoir. To 
withdraw or open the slide two inches for die inspection or the like, the 
solenoid of valve 45 is de-energized, oil is supplied through ports P and 
B to upper cavity 50 and the oil in lower cavity 46 is returned to the 
reservoir through port A and P of solenoid valve 45. 
Also shown in the barrel 16 at the right-hand side of the drawing is the 
connection screw 13 which is employed to make shut height adjustments. The 
connection screw 13 has two threaded portions. The upper threaded portion 
engages the threads in the hydraulic withdrawal and overload piston 24 and 
the lower threaded portion engages the threads in the threaded lock nut 
26. When oil is present in the lower cavity 46 these two parts are forced 
apart to take up clearances in the threads and thus lock the shut height 
adjustment mechanism in position. 
A typical embodiment of the present invention has been described herein and 
shown in the accompanying drawing to illustrate the underlying principles 
of the invention, but it is to be understood that numerous modifications 
may be made without departing from the broad spirit and scope of the 
invention.