Force multiplying press

A press for performing a work operation on a workpiece including a yoke defining a central bore, a ram mounted for reciprocal movement in the bore and carrying a fabricating tool on one end of the ram, an electric motor secured to an end wall of the yoke and having an output shaft passing through the end wall of the yoke, a ball screw driven by the output shaft of the motor and positioned in the bore of the yoke, a ball nut mounted in the bore on the ball screw, and a force multiplying mechanism interconnecting the ball nut and the ram and operative to move the ram to a preparatory position and thereafter multiply the force applied to the ram to facilitate the performance of the work operation. The force multiplying mechanism includes a linkage system interconnecting the nut and the ram and including a final link which moves into position in proximity of the line of action of the ram as the tool reaches its working position so that subsequent movement of the link toward the line of action multiplies the force exerted on the ram and thereby on the tool. The electric motor is an AC servo motor and and AC servo controller is provided for coaction with the motor to enable the motor to be precisely programmed to provide a predetermined number of revolutions to the ball screw so as to provide a predetermined desired forward stroking movement of the force multiplying mechanism.

BACKGROUND OF THE INVENTION 
This invention relates to presses and more particularly to presses for 
performing a work operation on a workpiece. 
Presses are commonly used in our industrial society for a myriad of 
mechanical fabricating operations such as piercing, punching, shape 
forming, resistance welding or the like. Various presses have been 
proposed and utilized to perform the various mechanical fabricating 
operations with the particular form and configuration of the press 
generally dictated by the particular application envisioned. Whereas a 
multitude of press designs have been proposed and in some cases 
commercially exploited, all of the prior art presses have had certain 
disadvantages. Generally, presses in which a large force is required to 
perform the desired fabrication operation have tended to be unduly large 
and cumbersome and, conversely, smaller, less cumbersome presses are 
unsatisfactory where a large force is required to perform the desired 
fabrication operation. 
Various attempts have been made to provide a relatively small press capable 
of generating a relatively high force at the fabricating tool but the 
commercial application of these presses has been limited by problems 
related to leakage, durability and the like. 
SUMMARY OF THE INVENTION 
This invention is directed to the provision of a relatively small press 
capable of generating relatively large fabricating forces. 
The invention press is usable in performing a work operation on a workpiece 
such for example as piercing, punching, shape forming or welding. The 
press of the invention includes a frame defining a bore; a ram slidably 
mounted in the bore and having a first end positioned within the bore and 
a free end projecting out of the bore; a fabricating tool mounted on the 
ram free end; an electric motor including an output shaft rotated in 
response to actuation of the motor; a drive member movable through power 
and return strokes in response to rotation of the output shaft; and a 
force multiplying mechanism interconnecting the drive member and the ram 
and operative in response to power stroking movement of the drive member 
to move the fabricating tool to a working position and thereafter multiply 
the force applied to the tool to facilitate the performance of the work 
operation. This arrangement allows a relatively small press to generate a 
relatively large force at the fabricating tool. 
According to a further feature of the invention, the ram and the drive 
member are mounted for movement on parallel axes so that forward stroking 
movement of the drive member produces forward stroking movement of the ram 
and the force multiplying mechanism comprises a linkage system 
interconnecting the drive member and the ram and transmitting the forward 
stroking movement of the driver member to the ram. This arrangement 
provides a convenient and efficient means for effecting the force 
multiplying function. 
According to a further feature of the invention, the linkage system 
includes a first link connected at one end thereof to a connection point 
on the ram and movable in response to forward stroking movement of the 
piston from a rest position, in which the other end thereof is displaced 
from a line of action parallel to the axes of the ram and drive member and 
passing through the connection point on the ram, to a working position in 
which the other end of the link is proximate the line of action. This 
arrangement provides a ready and efficient means of multiplying the force 
applied to the ram as the link approaches the line of action. 
According to a further feature of the invention, the linkage system further 
includes a second link pivoted at a first point thereon about an axis 
positioned on the line of action and fixed with respect to the frame and 
pivotally connected at a second point thereon to the other end of the 
first link. This arrangement provides a convenient means of transmitting 
the force from the drive member to the force multiplying link. 
According to a further feature of the invention, the linkage system further 
includes a third link pivoted at one end thereof to the drive member and 
pivoted at the other end thereof to a third point on the second link. This 
arrangement further facilitates the transmittal of motion and power from 
the drive member to the force multiplying link. 
According to a further feature of the invention, the first, second and 
third points on the second link are triangulated. This specific geometric 
configuration further optimizes the efficiency of the linkage system. 
According to a further feature of the invention, the second link has a 
triangular configuration with the first, second and third points 
positioned respectively at the three corners thereof. 
According to a further feature of the invention, the motor comprises a 
power cylinder including a piston and a piston rod; the output shaft of 
the press is constituted by the piston rod of the power cylinder; and the 
drive member is mounted on the free end of the piston rod. This 
arrangement allows the motor to be utilized to precisely and programmably 
control the movement of the force multiplying linkage through its various 
positions. 
According to a further feature of the invention, the press further includes 
control means operative to initially energize the motor in a high speed 
sense, whereby to move the force multiplying mechanism rapidly from its 
rest position to its preparatory position and thereby move the tool from 
its rest position to its preparatory position, and thereafter energize the 
motor in a slow speed sense, whereby to move the force multiplying 
mechanism to its final force multiplied position and thereby move the tool 
to its final position to perform the work operation. This arrangement 
allows the force multiplying mechanism to quickly move to its preparatory 
position whereafter the force may be dramatically increased to perform the 
desired work operation. 
According to a further feature of the invention, the press further includes 
a screw drivingly connected to the output shaft of the electric motor and 
the drive member comprises a nut mounted on the screw. This arrangement 
provides a convenient and efficient means of transmitting the rotary 
motion of the output shaft of the electric motor to forward linear 
movement of the force multiplying mechanism. 
According to a further feature of the invention, the screw is a ball screw 
and the nut is a ball nut. This specific arrangement further facilitates 
the efficient conversion of the rotational movement of the output shaft of 
the electric motor to forward linear movement of the force multiplying 
mechanism. 
According to a further feature of the invention, the electric motor is a 
brushless AC servo motor and the control means to the servo motor 
comprises a servo controller capable of being programmed to initially 
energize the motor in a first sense to provide a high speed operational 
mode to quickly move the force multiplying mechanism from its rest 
position to its preparatory position and thereafter energize the motor in 
a low speed sense to move the force multiplying mechanism from its 
preparatory position to its final working position. 
According to a further feature of the invention, the control means of the 
motor is capable of being programmed to count the revolutions of the motor 
and provide a predetermined number of revolutions corresponding to a 
predetermined desired travel for the force multiplying mechanism. With 
this arrangement, the control can be programmed to provide a predetermined 
number of revolutions of the motor corresponding to the required distance 
of movement of the force multiplying mechanism for a particular 
application and can be readily reprogrammed to provide a different number 
of revolutions corresponding to the requirements of a different 
application.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The invention press, broadly considered, comprises a yoke or frame 10, a 
ram 12, an electric motor 14, a drive member 16, a force multiplying 
mechanism 18, first and second fabricating tools 20 and 22, and a base 24. 
Yoke 10 is formed of steel plates and has a cage configuration with a 
generally C-shape in longitudinal cross section. Yoke 10 includes 
generally C-shaped side plates 26 and 28, a top plate 30, a rear end plate 
32, a bottom plate 34, and a die retainer plate 36. Plates 26, 28, 30, 32, 
34 and 36 are suitably joined together, as for example by bolting, to form 
a C-shaped cage structure defining a generally rectangular blind bore 38 
opening adjacent the forward end of the yoke and closed at its rearward 
end by rear end plate 32. Side plates 26 and 28 will be seen to include 
cutouts 26a and 28a defining the C-configuration of the plates and will be 
seen to extend downwardly below bottom plate 34 to form skirt portions 26b 
and 28b. 
An auxiliary cage structure 40 is suitably secured to the rear end of the 
yoke. Cage structure 40 may include for example side plates 42 and 44 and 
end plate 46 suitably secured to each other and suitably secured to the 
rear face of end plate 32 of the yoke so as to define an open rear chamber 
48. 
Ram 12 is formed as a monolithic rectangular steel block with a 
cross-sectional configuration conforming to the cross-sectional 
configuration of bore 38 so that ram 12 may reciprocate smoothly within 
bore 38. Ram 12 is selectively hollowed out along its axial length to 
provide a central chamber 50 opening at the rear face of the ram and 
parallel core passages 12a and 12b extending axially forwardly from the 
forward end of chamber 50 and opening in the front face 12c of the ram. 
Ram 12 further includes an axial bore 12d positioned between core passages 
12a and 12b and extending forwardly from chamber 50 to the front face 12c 
of the ram; a bore 12e extending transversely of the ram and passing 
through core passages 12a and 12b, and a pair of parallel axially 
extending slots 12f and 12g defined respectively in the side wall portions 
12h and 12i of the ram in horizontal alignment with transverse bore 12e. 
Motor 14 comprises a brushless AC servo motor such for example as the type 
available from Rexroth Indramat of Woodale, Illinois as Part No. 
MAC90-COKD-2X-100-A. Motor 14 is suitably secured to the rear exterior 
face of cage plate 46 and includes an output shaft 54 extending forwardly 
and passing through plate 46 for entry into chamber 48. 
Drive mechanism 16 includes a coupling 56, a ball screw 58 and a ball nut 
60. Coupling 56 may comprise a taper lock chain coupling of the type 
available from Dodge Manufacturing Corporation of Michawa, Indiana as Part 
No. 4016 TYPE HF and includes a first sprocket member 62 secured to the 
forward end of motor output shaft 54, a second sprocket member 64 secured 
to the rearward end of ball screw 58, and a double chain 66 comprising a 
double width standard precision chain and extending around and in driving 
engagement with sprocket 62 and 64 so as to drivingly couple the output 
shaft 54 of motor 14 to the rear end of ball screw 58. Ball screw 58 is 
journaled at its rearward end by bearings 68 provided in yoke end wall 32 
and extends forwardly through bore 38 of yoke 10 and through central 
chamber 50 of the ram 12 for journaling receipt at its forward end 58a in 
a bushing 69 positioned in bore 12d of the ram. 
Ball nut 60 has a generally rectangular configuration and includes trunions 
60a extending from opposite side faces of the nut. Ball screw 58 and ball 
nut 60 may for example be of the recirculating ball type including, in 
known manner, balls which roll along arch-shaped ball running grooves in 
the ball screw and in the nut and arranged, after running several times 
around the shaft, to be passed through a ball tube incorporated in the nut 
so as to be recirculated. Ball screw 58 and ball nut 60 may for example be 
of the type available from THK Co. Ltd. of Tokyo, Japan as Assembly No. 
BSF2510B. It will be understood that rotation of motor output shaft 54 
acts through the intermediary of coupling 56 to rotate ball screw 58 which 
in turn causes ball nut 60 to move linearly along the ball screw. 
Force multiplying mechanism 18 includes a first link means comprising a 
pair of links 70 and 72, second link means comprising a link 74, and third 
link means comprising a pair of links 76 and 78. Links 70 and 72 are 
generally straight and are each journaled at their rearward ends on a 
respective trunion 60a of ball nut 60 and pivotally secured at their 
forward ends to link 74 by pivot pins 80 carried by link 74 adjacent one 
corner of the link. 
Link 74 has a generally triangular configuration and has a bifurcated 
construction, including spaced side walls 74a and 74b, for passage of ball 
screw 58. A fixed shaft 82 extends fixedly between side walls 26 and 28 of 
yoke 10 for passage through slots 12f and 12g in the side walls of the ram 
and for pivotal passage through the upper solid apex of triangular member 
74. Member 74 further includes pivot pins 84 at the third apex of the 
member. 
Links 76 and 78 are generally straight and are respectively pivotally 
secured at their rearward ends to pivot pins 84 and extend at their 
forward ends into the respective core passages 12a and 12b of the ram for 
pivotal mounting at their forward ends on a pivot shaft 86 extending 
transversely of the forward end of the ram within transverse bore 12e. The 
center of shafts 82 and 86 define a line of action 88 parallel to the 
central longitudinal axis of ball screw 58. 
Fabricating tool 20, which may comprise for example a punch, is mounted on 
an adapter member 90 suitably secured to the forward end of ram 12 in 
overlying relation to core passages 12a and 12b, and fabricating tool 22, 
which may comprise for example a collet, is suitably secured to the 
rearward face of die retainer plate 36 in aligned relation to punch 20 so 
as to coact with punch 20 to perform a punching operation on a workpiece 
positioned therebetween in response to actuation of motor 14. 
Yoke 10 is suitably mounted on base member 24 for reciprocal movement 
relative to the base member with linear bearings 92 interposed between 
base 24 and the lower face of yoke bottom plate 34 to facilitate the 
smooth reciprocal movement of yoke 10 on base 24 so that the invention 
press may operate in a self-equalizing manner upon actuation of motor 14 
to apply equal forces to the opposite sides of a workpiece positioned 
between fabricating tools 20 and 22 to avoid undesirable inelastic 
deformation of the workpiece during the work operation performed by the 
fabricating tools 20 and 22. Further details of the manner in which yoke 
10 may be mounted on base 24, as well as further details of the manner in 
which the yoke 10 coacts with the base 24 to facilitate a self-equalizing 
work operation, are disclosed in U.S. Pat. No. 4,716,803, assigned to the 
assignee of the present application as well as in United States patent 
application Ser. No. 859,016 filed on May 2, 1986 and also assigned to the 
assignee of the present application. 
In the operation of the invention press, the force multiplying mechanism, 
in response to actuation of motor 14, moves from the retracted or rest 
position seen in FIGS. 4 and 5 to a preparatory position indicated by the 
solid line position of the force multiplying mechanism in FIG. 2, and 
thereafter moves to a final position as seen in the dotted line position 
seen of FIG. 2. The initial forward stroking movement of the force 
multiplying mechanism, and the vast majority of the forward stroking 
movement, accomplishes a gross or macro movement of the fabricating tool 
20 into a preparatory position relative to fabricating tool 22 and 
relative to a workpiece positioned therebetween, and the final forward 
stroking movement of the force multiplying mechanism accomplishes a micro 
movement of the tool 20 to its final position while acting to multiple the 
force supplied to the fabricating tool to facilitate the performance of 
the work operation. 
Specifically, with the force multiplying mechanism in the rest or retracted 
position of FIGS. 4 and 5, the rear ends of links 76 and 78 are grossly 
displaced relative to the line of action 88 passing through pins 82 and 
86. As ball screw 60 begins its forward stroking movement in response to 
actuation of motor 14, links 70, 72 move forwardly to pivot triangular 
link 74 about the axis of fixed pin 82 to move links 76,78 forwardly in a 
manner to move the ram forwardly through the intermediary of pin 86 and 
thereby move the fabricating tool 20 to its preparatory position. The 
various parts are configured and designed such that the tool 20 arrives at 
its preparatory position relative to the workpiece at such time as links 
76,78 assume an angle .theta. with respect to line of action 88 of 
approximately 7.degree.. Further forward stroking movement of the ball nut 
60 has the effect of multiplying the force exerted at the tool 20 as the 
center of pivot pins 84 moves closer and closer to the line of action 88. 
Preferably, the center of pins 84 never quite reaches the line of action 
88 but rather has a final disposition in which links 76,78 assume an 
approximately 1.degree.angular disposition with respect to line of action 
88. The force applied to tool 20 and thereby to the workpiece may thereby 
be multiplied by a factor, for example, of from 20 to 4 times so that a 
relatively small magnitude of torque applied by motor 14 has the effect of 
applying an extremely large force at the tool 20 to perform even extremely 
heavy-duty fabricating operations. As indicated, the invention press is 
preferably arranged and designed to operate in a self-equalizing manner so 
that the forces exerted on the workpiece by fabricating tools 20 and 22 
are essentially equal but the invention press may also be operated without 
the force equalizing feature. 
According to a further important feature of the invention, control means 
are provided for motor 14 which enables the motor to operate in 
conjunction with the force multiplying mechanism 18 so as to precisely 
position the fabricating tool 20 relative to the fabricating tool 22 in 
response to a predetermined input signal to the motor. For example, 
control means may be provided to initially energize the motor in a 
relatively high speed sense so as to move the motor rapidly from its rest 
or retracted position to its preparatory position whereafter the motor may 
be energized in a relatively low speed mode to move the force multiplying 
mechanism from its preparatory position to its force multiplying position. 
The control means 100 provided in conjunction with motor 14 may for 
example comprise a pulse width modulation servo controller of the type 
available from Rexroth Indramat as TDMAC servo controller Part No. 
MAC90-COKD-2X-100-A-O. Controller 100 is capable of being programmed, for 
example, to provide a specified number of revolutions of servo motor 14 so 
that, given the known axial distance the ball nut moves in response to 
each rotation of the ball screw, a predetermined amount of forward 
movement of tool 20 relative to tool 22 may be programmed simply by 
programming controller 100 to provide a predetermined number of 
revolutions of the motor. The motor may be operated at a constant speed 
during the entire movement of the force multiplying mechanism from its 
rest position and through its preparatory position to its final force 
multiplied position but, preferably, controller 100 is programmed to 
provide a two-part movement of the force multiplying mechanism wherein the 
initial movement of the force multiplying mechanism from its rest to its 
preparatory position is at a relatively high speed and the final movement 
from its preparatory to its force multiplied position is at a relatively 
low speed. For example, in a typical application, the ball nut moves three 
inches between its retracted and preparatory positions and .06 inches 
between the preparatory and final force multiplied position of the force 
multiplying mechanism and the motor is programmed to move the ball nut at 
180 inches per minute during the movement of the ball screw from its 
retracted to its preparatory position and to thereafter move the ball 
screw at two inches per minute during the movement of the force 
multiplying mechanism from its preparatory to its final force multiplied 
position. With these parameters, and allowing for acceleration and 
deceleration times, the movement of the force multiplying mechanism from 
its rest to its preparatory position requires 1.3 seconds and the movement 
of the force multiplying mechanism from its preparatory to its final force 
multiplied position requires 1.8 second for a total cycle time of 3.1 
seconds. 
The invention press will be seen to provide a compact and efficient 
mechanism for applying a large force to a fabricating tool to perform even 
heavy-duty work operations while requiring only a relatively small and 
readily available electrical energy input at the actuation end of the 
press. For example, the invention press may be designed so that a force of 
600 lbs. provided at ball nut 60 in response to rotation of the ball screw 
will result in the application of a force of 12000 lbs. at the tool 20. 
Whereas a preferred embodiment of the invention has been illustrated and 
described in detail it will be apparent that various changes may be made 
in the disclosed embodiment without departing from the scope or spirit of 
the invention.