Machine tool stroke control system

A unique system and process for controlling the stroke positions of tools on a multi-station metal working machine are disclosed. The system and process are suitable for use with a metal working machine which carries the tools on an arm pivoted by an actuator. In the preferred embodiment, the control system includes a control circuit which continuously senses the position of the arm by use of a pulse generator rotary encoder. The control system stores settable initial and final stroke positions for each of the tools. The actuator is controlled to move the arm and the tools carried thereon.

TECHNICAL FIELD 
This invention relates to a system and process for controlling the stroke 
positions of tools on a multi-station metal working machine. 
BACKGROUND OF THE INVENTION AND TECHNICAL PROBLEMS POSED BY THE PRIOR ART 
Machine shops, structural steel plants, manufacturing facilities, and the 
like may employ machines for shearing metal workpieces, such as steel 
stock of various shapes and sizes. One type of machine, commonly known as 
an "ironworker" or "universal steelworker", performs various different 
metal working processes on workpieces at various separate stations. 
Typically there is a punching station for punching holes or other shapes, 
a notching station for notching the edge of a workpiece, and a bar stock 
shearing station for shearing lengths of round or square bars or flat 
stock. 
An example of such an ironworker design is described in the U.S. Pat. No. 
3,866,522. The ironworker machine employs a single, large arm or beam 
which is pivotally mounted to a frame and which is operated with a 
hydraulic piston and cylinder actuator. The various stations, such as a 
punching station,.a shearing station, and a notching station, are defined 
at various locations along the length of the pivotally mounted beam. At 
each station, a particular tool is mounted on the beam for movement with 
the beam relative to a die or other, cooperating, fixed tool on the frame. 
Such an ironworker design provides the advantages of simple operation and 
low cost. 
In a typical arrangement of the conventional pivoting beam ironworker 
machine, the height to which the cutting or punching tool rises above the 
workpiece, the top of stroke position, must be set according to the 
thickness of the workpiece. To facilitate meeting safety standards, as 
well as workplace efficiency requirements, manual push buttons, selector 
switches, foot switches and limit switches are provided to control the 
operation of the various tools. 
Typically, one pair of limit switches is provided for each tool. The limit 
switches are positioned to correspond to the top and bottom of stroke 
positions and are used, through relay control logic circuits, to stop and 
reverse tool movement, respectively. However, each time the thickness of 
the workpieces change, the limit switches must be reset to account for the 
reduced or increased stroke required. Accordingly, it would be desirable 
to provide an improved system and process for controlling the stroke 
positions of the various tools on a multi-station metal working machine 
without the use of limit switches. This would permit efficient setting of 
the top and bottom stroke positions without the necessity to reset limit 
switches often. 
The present invention provides an improved system and process for sensing 
and controlling the stroke positions of various tools on a multi-station 
metal working machine. The improved system and process accommodate 
continuous sensing of stroke position and provide for readily resettable 
top and bottom stroke positions without the necessity to reset limit 
switches. 
SUMMARY OF THE INVENTION 
An apparatus in accordance with the teaching of the present invention 
provides a novel system and process for controlling the stroke positions 
of tools on a multi-station metal working machine. The tools are carried 
on an arm of the machine which is operatively connected to an actuator for 
moving the arm between selectable initial stroke positions (e.g., top of 
stroke) and final stroke positions (e.g., bottom of stroke) for each of 
the tools relative to a workpiece. 
The system includes a sensor for continuously sensing the position of the 
arm. A signal generator generates a position signal which corresponds to 
the sensed position of the arm. The position signal has a value that 
varies with, and is representative of, the position of the arm. 
The actuator actuates upon a start signal and moves the arm from its 
initial stroke position for the selected tool. A control circuit responds 
to the position signal and generates at least one control signal for 
controlling the operation of the actuator in response to the position 
signal being representative of one selected stroke position (e.g., the 
final stroke position). Preferably, the control circuit also generates 
another control signal for controlling the operation of the actuator in 
response to the position signal being representative of another selected 
stroke position (e.g., the initial stroke position). 
In a preferred embodiment, the machine includes a pivotally mounted arm, 
and the machine includes a shaft which is rotated by the actuator and 
includes a linkage connected between the shaft and the arm to pivot the 
arm. The sensor is incorporated in a pulse generator rotary encoder which 
is operatively connected to the shaft. The position signal generator 
includes a circuit which is associated with the encoder to produce a 
position signal in the form of a cumulative pulse signal which is 
representative of the angular position of the shaft which in turn is 
representative of the arm position. 
The control circuit in the preferred embodiment includes initial and final 
programmable registers which are associated with each tool. The initial 
register is settable at a selected value which corresponds to a cumulative 
pulse signal associated with the selected initial stroke position. 
Similarly, the final register is settable at a selected value which 
corresponds to a cumulative pulse signal associated with the selected 
final stroke position. This preferred embodiment includes means which are 
responsive to the cumulative pulse signal for generating a first control 
signal when the cumulative pulse signal equals the final register selected 
value. Similarly, the means are responsive to the cumulative pulse signal 
for generating a second control signal when the cumulative pulse signal 
equals the initial register selected value. 
In this preferred embodiment, the first control signal reverses the 
direction of the operation of the actuator to move the arm to carry the 
selected tool back toward the initial stroke position. The second control 
signal terminates the operation of the actuator with the selected tool at 
the initial stroke position. 
Numerous other advantages and features of the present invention will become 
readily apparent from the following detailed description of the invention, 
from the claims, and from the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
While this invention is susceptible of embodiment in many different forms, 
this specification and the accompanying drawings disclose only some 
specific forms as examples of the invention. The invention is not intended 
to be limited to the embodiments so described, however. The scope of the 
invention is pointed out in the appended claims. 
For ease of description, the apparatus of this invention is described in 
the normal (upright) operating position, and terms such as upper, lower, 
horizontal, etc., are used with reference to this position. It will be 
understood, however, that the apparatus of this invention may be 
manufactured, stored, transported, used, and sold in an orientation other 
than the position described. 
Figures illustrating the apparatus show some electrical and mechanical 
elements that are known and that will be recognized by one skilled in the 
art. The detailed descriptions of such elements are not necessary to an 
understanding of the invention, and accordingly, are herein presented only 
to the degree necessary to facilitate an understanding of the novel 
features of the present invention. 
An exemplary iron worker machine tool having a system to control the stroke 
positions of tools thereon is illustrated in FIG. 1 and is designated 
generally therein by the reference number 10. One such suitable machine 10 
on which the system may be employed is disclosed in the commonly assigned 
U.S. patent application Ser. No. 08/073,123 filed Jun. 7, 1993, now U.S. 
Pat. No. 5,394,732. A detailed description of portions of the machine 10 
is provided in that U.S.A. patent application. However, various detailed 
design features form no part of the present invention and are described 
herein only to the extent necessary for an understanding of the present 
invention. 
The machine 10 has a frame 12 and a main pivoting beam or first arm 14 
mounted to the frame 12 with a central bearing assembly 16 for pivoting 
about a first axis 18. The bearing assembly 16 may be of any conventional 
or special design. 
With particular reference to FIG. 1, the left-hand end 20 of the arm 14, 
together with the frame 12, defines a punching station 22. The punching 
station 22 contains a conventional punch holder 24 and punch 26 which are 
carried on the arm 14. Stationary die components 28 are mounted in the 
frame 12 below the arm left-hand end 20, and an adjustable height stripper 
30 is also provided. 
The right-hand end 32 of arm 14, together with the frame 12, defines a 
notching station 34 containing a conventional upper blade 36 and lower 
blade 38. 
The central portion 40 of arm 14, together with the frame 12, defines a 
shearing station 42 which contains, as illustrated in FIG. 1, an 
adjustable shearing blade assembly comprising a stationary blade assembly 
46 and a movable blade assembly 48 which is mounted to a second arm 50 
that is pivotably mounted on the first arm 14. In other, more simple 
designs (not illustrated), the second arm 50 could be eliminated, and the 
shear blade 48 could be mounted directly to the first arm 14. 
The punching station 22, notching station 34, and shearing station 42 are 
selectively operated by pivoting the main arm 14 as necessary to move the 
tools carried thereon into and out of the workpiece in a well-known 
manner. The pivoting motion of the arm 14 is represented by the 
double-headed arrow 51 in FIG. 1. 
The system for pivoting the arm 14 includes a pair of parallel links 52 
(only the near one is visible) which are pivotally connected with a pin 54 
to the right-hand end 32 of arm 14, just inwardly of notching station 34. 
The lower end of each link 52 is pivotally connected with a second pin 56 
to a crank arm 58 which is pivotally mounted to the frame 12 with a shaft 
60 (FIG. 2). The frame 12 includes two side plates 59, and the shaft 60 is 
mounted for rotation in bearings 57 carried by the side plates 59. 
The lower end of crank arm 58 is pivotally connected to an actuator 62, 
such as a conventional double acting hydraulic piston-cylinder actuator, 
for pivoting the crank arm 58 about the shaft 60 in a selected direction 
of rotation as indicated by the double-headed arrow 61 shown in FIG. 1. 
Shaft 60 rotates with movement of crank arm 58 relative to frame 12. 
Specifically, crank arm 58 pivots with shaft 60 which is pinned thereto by 
a pin 63 such that shaft 60 and crank arm 58 are fixed relative to each 
other. 
Thus, depending upon whether the cylinder-piston actuator 62 is retracted 
or extended, the first arm 14 pivots counterclockwise or clockwise, 
respectively (as viewed in FIG. 1), in the central bearing 16 to effect 
the punching process at the punching station 22, the notching process at 
the notching station 34, or the shearing process at the shearing station 
42. The use of a double acting piston-cylinder actuator to pivot a main 
arm 14 for operating a punching station, a notching station, or a shearing 
station is well-known in the art. 
In a preferred embodiment, as illustrated in FIGS. 1 and 2, a pulse 
generator rotary encoder 64 is mounted to one of the side plates 59. The 
encoder 64 used in this application can be a standard, commercially 
available, single channel, pulse output type. However, the 
once-per-revolution, home position marker is preferably modified in this 
embodiment in accordance with the present invention as described in detail 
hereinafter. With the exception of the modified home position marker, the 
detailed design and operation of such an encoder 64 will be understood by 
those skilled in the art and form no part of the present invention. In the 
disclosed embodiment, the encoder 64 is a model HD20 
SM-600-24LD-SCB-1-S10253-600, manufactured by Lucas Control Systems 
Products which has an office in Bloomingdale, Ill., U.S.A. 
With particular reference to FIG. 3, the encoder 64 comprises a bearing 
housing assembly 66, a light-emitting diode ("LED") light source 68, input 
shaft 70, transparent code disk 72 with evenly spaced opaque lines 73, a 
stationary mask 74, photocell detector assembly (i.e., photodetector) 76, 
electronics board 78, cover 80, and electrical connector 82. In the 
illustrated encoder 64, the code disk 72 is mounted to the encoder input 
shaft 70 while the light source 68, mask 74, and photocell detector 
assembly 76 are stationary in the cover 80. 
As the encoder input shaft 70 and code disk 72 rotate, the light received 
by the photocell detector assembly 76 is interrupted by the opaque lines 
73. A signal is generated each time the light is received by the photocell 
detector assembly 76. The signal generated by the photocell detector 
assembly 76 may be produced in the form of a quasi-sine wave output which 
is converted in the encoder to a square wave form for transmission to a 
counter. 
A single control mark 77 is also provided on the periphery of the code disk 
72 to mark a reference position as sensed by the photocell detector 
assembly 76. This produces a marker pulse output in a separate channel 
which switches between on and off only once per input shaft revolution 
according to conventional techniques. The marker pulse is used to 
recalibrate the control system and reset counters in the control system as 
described in detail hereinafter. 
Although the control mark on an encoder typically has a relatively short 
arc length, the inventor of the present invention has discovered that a 
short mark does not work well in some situations with the ironworker type 
machine. According to a preferred form of the present invention as 
incorporated in such a machine, a novel, longer arc control mark 77 has 
been developed. The arc length of the control mark may be, for example, 
sufficient to produce a marker pulse corresponding to between about 20 
degrees and about 60 degrees of encoder rotation. In one contemplated 
embodiment, the control mark 77 has a width of about 320 degrees to 
produce a marker pulse of about 40 degrees. At each end of the 40 degree 
marker pulse signal a change of state occurs (i.e., off to on or on to 
off), and this is recognized by the control system. 
As best seen in FIGS. 1 and 2, encoder 64 is mounted to one of the side 
plates 59 with bolts 84 inserted through mounting holes 85 (FIG. 3) in the 
bearing housing 66, or by other suitable means. The encoder input shaft 70 
is operably connected to the machine shaft 60 by a coupling 86 or other 
means to assure that input shaft 70 and shaft 60 can rotate together as a 
unit. 
The encoder 64 is electronically connected to a programmable logic 
controller (PLC) 88 (FIG. 2). The programming and capabilities of PLCs are 
not described in detail herein but are well-known to those skilled in the 
art. The PLC 88 is operably connected to the control system, and is to be 
provided with input electrical signals from the encoder 64. 
A tool selector switch or mode switch 90 is provided for selecting the 
station (notching 34, shearing 42, or punching 22) to be operated through 
the PLC 88. 
A main power switch 87 is included in the control circuit. When the power 
is switched on, the operator must first control the actuator 62 to perform 
a reference sequence operation of the machine (as described in detail 
hereinafter). This initially locates the hydraulic piston of the actuator 
62 so that the encoder shaft 70 corresponds with either end of the 40 
degree marker pulse of the encoder 64. The 40 degree marker pulse signal 
of the encoder 64 terminates at each end of the 40 degree arc at positions 
that correspond to positions of the arm 14 near either end of the travel 
of the actuator 62 and main pivot arm 14. Thus, the marker pulse 
corresponds to a major portion of the travel or stroke of the arm 14. 
The termination of the marker pulse at each end of the pulse is a change of 
state that resets a pulse signal counter in the PLC 88 and recalibrates 
the PLC 88 each time the marker pulse terminates. This permits control of 
the machine even for relatively thin workpieces with an encoder that might 
"miss" a pulse or two in operation. The ends of the 40 degree marker pulse 
would correspond to positions of the arm 14 beyond the narrow central 
region containing the thin workpiece. 
Movement of the actuator 62 away from the 40 degree marker pulse end point 
position generates pulse signals in the encoder normal channel. The PLC 88 
counts the pulses as representative of the arm position away from the 
position corresponding to the marker pulse end point position of the 
actuator 62. 
The PLC 88 has arithmetic register 91, 92, 93, 94, 95 and 96. These can 
each be programmed or set to store the value of the encoder position 
signal corresponding to selected stroke positions such as the initial, or 
top of stroke, position, and the final, or bottom of stroke, position. 
Additional registers can be employed if desired (e.g., to temporarily save 
tool positions unique to a particular workpiece thickness at a selected 
station). 
In a preferred system arrangement, registers 91 and 92 can be set to the 
initial and final stroke positions, respectively, of the notcher upper 
blade 36. Registers 93 and 94 can be set to the initial and final stroke 
positions, respectively, of the movable shear blade assembly 48. Registers 
95 and 96 can be set to the initial and final stroke positions, 
respectively, of the punch 26. For example, if the notcher top of stroke 
position corresponds to a 100 pulse signal from the encoder marker pulse, 
then the value of 100 can be set in the notcher initial register 91. An 
analogous procedure can be used to set the bottom of stroke position in 
the notcher register 92. 
The control system also preferably includes an up and down jog switch 102 
and companion emergency stop switch 104 near the notching station 34 and 
shearing station 42. Another up and down jog switch 106 and companion 
emergency stop switch 108 are located near the punching station 22. 
The jog switches 102 and 106 operate appropriate, electrically actuated 
valves (not illustrated) in the hydraulic actuator system to pressurize 
the hydraulic actuator 62 in a selected direction. The control system 
prevents automatic cycling of the machine until the arm 14 is located near 
one of its two end of travel positions corresponding to one end or the 
other of the 40 degree marker pulse signal. This is accomplished by 
operating the machine through an initial reference sequence. 
To this end, when the main power switch 87 is turned on, the operator must 
first simultaneously press the up and down buttons on either one of the 
jog switches 102 or 106. This causes the control system to operate the 
actuator 62 until the encoder 64 rotates to either end of the reference 
mark at which time the 40 degree marker pulse signal changes state. At 
that point the arm 14 is near one end or the other of its travel. The 
control system terminates the operation of the actuator 62 when the marker 
pulse signal changes state so as to initially maintain the arm 14 at one 
of the two corresponding positions near either end of its travel. This 
must be done each time the power switch 87 is turned on to enable 
subsequent automatic cycling of the machine. However, once the reference 
sequence has been performed, it does not have to be repeated unless the 
main power switch 87 is turned off. Thus, the mode switch 90 may be 
changed and other operations performed (as explained in detail 
hereinafter) without repeating the reference sequence for each mode. 
Thereafter, the individual operation of each jog switch 102 or 106 
positions the arm to a desired initial stroke position for a selected 
tool. In particular, jogging the switch 102 up or down retracts or 
extends, respectively, the actuator 62 to raise or lower, respectively, 
the end of the arm 14 at the notching station 34 and shearing station 42. 
Jogging the switch 106 up or down extends or retracts, respectively, the 
actuator 62 to raise or lower, respectively, the end of the arm 14 at the 
punching station 22. 
Upon termination of the actuation of a jog switch 102 or 106, the value of 
the initial (top of stroke) register for the selected tool (e.g., the 
notching station top of stroke register 91) is automatically set by the 
control system to the value of the encoder position signal. 
The control system also includes a foot switch 120 which, upon actuation, 
operates appropriate, electrically actuated valves (not illustrated) in 
the hydraulic actuator system, as selected by the mode switch 90, to 
pressurize the hydraulic actuator 62 in a selected direction. Other inputs 
may be employed to facilitate additional desired features of the system 
operation and control. 
In operation, the incremental rotational movement of the connected shafts 
60 and 70 is, in essence, "counted" by the encoder 64 which generates a 
pulse each time the opaque lines 73 of the encoder disk 72 interrupt the 
light beam directed from the light source 68 to the photocell detector 
assembly 76. The pulses may be in the form of a quasi-sine wave output 
converted by the encoder to a square wave form. The square wave form 
pulses are transmitted to the PLC 88 and counted. The PLC 88 processes the 
cumulative pulse signal as being representative of the position of the 
main arm 14 at any given time. Additionally, the pulse signals produced by 
the encoder 64 are dependent upon the direction of rotation, such that the 
pulse signals to the PLC 88 do not accumulate in an absolute sense, but 
are added to or subtracted from, the total dependent upon the direction of 
rotation of the input shaft 70. 
The set-up and operation of the apparatus of the present invention will be 
described for four different operations of the machine. The machine is 
capable of operating in the following different modes: notching, shearing, 
spot mode punching, and auto mode punching. Set-up and operation of the 
machine will be described for the notching, shearing, spot mode punching, 
and auto mode punching operations. It should be noted that set-up and 
operation in the notching and shearing modes is essentially identical with 
respect to the control system and process except that the tool selector 
switch 90 is set to the appropriate operation. 
Notching Operation 
The notching operation is used for notching all shapes of steel stock. 
First, the machine 10 is turned on with the main power switch 87. The 
machine must be initially operated through a reference sequence. To this 
end, the operator drives the arm 14 to a position near either end of its 
travel by simultaneously pressing the up and down buttons of the jog 
switch 102 (or, alternatively, jog switch 106). This, as explained above, 
operates the actuator 62 until the encoder forty degree marker pulse 
signal changes state (which corresponds to a position of the actuator 62 
holding the arm 14 near one end or the other of the arm travel). The 
control system is programmed to prevent subsequent automatic cycling of 
the machine unless this is done each time the main power switch 87 is 
turned on. 
The tool selector or mode switch 90 is then set to the "NOTCH" position. 
The workpiece to be notched is positioned in the notcher station 34 near 
the blade components 36. Then, the up/down jog switch 102 is operated as 
necessary to extend or retract the actuator 62 for positioning the upper 
notching blade component 36 just above the workpiece to provide sufficient 
clearance to move the workpiece into the proper position directly below 
the notcher blade 36. The efficiency of the process, especially where 
multiple, identical workpieces are to be notched is maximized by setting 
this "top of stroke" position as low as possible. The PLC 88 saves this 
position in the initial register 91 as the "top of stroke" position. This 
position is saved because the control system saves the last encoder pulse 
signal count in register 91 whenever the switch 102 is released while the 
mode switch 90 is set to "NOTCH". After the top of stroke position is set, 
the workpiece is moved to the proper location under the notcher blade 36. 
The foot switch 120 is then depressed which actuates the actuator 62 at 
high speed and high pressure. The actuator 62 cycles the upper notch blade 
36 toward the bottom of stroke position. The encoder pulse signal 
corresponding to the bottom of stroke position can be previously set 
(stored) in the final register 92 (by the manufacturer of the machine 10 
or by the operator using the jog switch 102). Thus, when the blade 36 
reaches the bottom of stroke position, the encoder pulse signal equals the 
stored value in the final register 92. At this position, the PLC 88 
generates a first control signal which reverses the direction of the 
actuator 62, and the upper notcher blade 36 is raised back toward the 
initial top of stroke position. 
When the upper notcher blade 36 reaches the initial, top of stroke 
position, the encoder pulse signal equals the stored value in the initial 
register 91. At that point, the PLC 88 generates a second control signal 
which stops the actuator 62 to maintain the upper notcher blade 36 at the 
initial (top of stroke) stroke position. 
For purposes of safe operation, the control circuit requires the foot 
switch 120 to be depressed at least until the bottom of stroke position is 
reached. Upon release of the foot switch 120 after the bottom of stroke 
position, the actuator 62 continues operation until the top of stroke 
position is reached. If the foot switch 120 is released before the bottom 
of stroke position is reached, then the actuator 62 is reversed by the PLC 
88 immediately, and the blade 36 is returned to the top of stroke 
position. 
After the top of stroke position is reached, the actuator 62 is stopped by 
the PLC 88 to hold the notcher blade 36 at the top of stroke position. The 
next workpiece can be notched merely by positioning the next workpiece in 
the notching station 34 and again depressing the foot switch 120. This 
second depression of the foot switch 120 cycles the upper notch blade 36 
to the bottom of stroke position through the workpiece and back to the 
initial stroke position previously set. 
To reset the initial, or top of stroke, position, the jog switch 102 is 
used to reset the initial register 91. Additionally, the bottom of stroke 
position can be changed and set in the final register 92 by the operator 
through use of the jog switch 102. As such, the control system of the 
present invention provides maximum operating flexibility combined with all 
necessary and prudent safety features. 
Shearing Operation 
The shearing operation is analogous in function and operation to the 
notching operation described above herein. If the main power switch 87 has 
not been turned off following a prior operation, the machine need not be 
run through the reference sequence (as explained above for the "Notching 
Operation"). On the other hand, if the machine main power switch 87 is 
first turned on for this shearing operation, then the reference sequence 
must be run. That is accomplished by first simultaneously pressing the up 
and down buttons of the jog switch 102 (or, alternatively jog switch 106). 
This moves the arm 14 to a position near one of its two ends of travel as 
explained above with respect to_the "Notching Operation." 
To commence shearing operation, the mode switch 90 is set to "SHEAR". The 
initial register 93 for the shearing operation, which represents the top 
of stroke position, is then set as previously described for the notching 
operation using jog switch 104. Similarly, the final register 94, which 
represents the bottom of stroke position, may be set by the machine 
manufacturer or by the operator. All other features and operations of the 
shearing operation are analogous to the notching operation. 
Spot Mode Punching Operation 
The spot mode punching operation is effectively used when punching a 
workpiece wherein the workpiece is positioned with the use of a template 
or with layout marks on the workpiece itself. The spot punching operation 
is next briefly provided with reference to FIGS. 4-6. The stripper 30 is 
adjustable relative to the punch holder 24 and punch 26. The stripper 30 
can be adjusted to vary the length of the punch 26 that projects beyond 
the stripper 30 in the initial, unactuated condition. 
In the set-up position which is illustrated in FIG. 4, the punch 26 is 
shown extending a pre-selected small distance beyond the stripper 30. 
In the extended or punching position which is illustrated in FIG. 5, the 
arm 14 has lowered the punch 26 to the fully extended, or bottom of stroke 
position, beyond the stripper 30 for maximum penetration of punch 26 into 
the workpiece (not illustrated). 
In the stripping position which is illustrated in FIG. 6, the punch 26 has 
been temporarily elevated above the bottom of the stripper 30. That is, 
the punch 26 retracts within the stripper 30. The retracted or stripping 
position is necessary because the punch may bind within the workpiece, and 
the stripper is engaged by the workpiece as the punch is withdrawn 
therefrom. 
If the main power switch 87 had been turned off, then the machine must be 
initially run through the reference sequence operation as explained above 
in detail relative to the "Notching Operation." If the main power switch 
87 had not been turned off following a prior operation, then the reference 
sequence need not be repeated. 
When the reference sequence has been established, the tool selector mode 
switch 90 is set to the "SPOT PUNCH" position. Preferably, a notcher guard 
(not shown) is located on the notching station 34 and electrically 
interlocked with the control system such that the notcher guard (not 
shown) must be closed in order for the machine to operate in the punch 
mode. The workpiece is then temporarily positioned with an end near, but 
not under, the punch 26. 
With the selector mode switch 90 in the "SPOT PUNCH" mode, the jog switch 
106 is used to operate the actuator 62 to adjust the punch position to 
just above the workpiece. The PLC 88 stores this position in the punch 
initial register 95 as the top of stroke position in generally the same 
manner as described above with respect to the notcher and its initial 
register 91. 
The workpiece is then moved fully under the punch in the punching station. 
The stripper 30 is then set to a position just above the workpiece with 
the punch 26 extending slightly therethrough. The workpiece can then be 
positioned for punching using a template or layout marks. The foot switch 
120 can be "tapped" to move the punch 26 down onto the layout mark or 
template. 
If the workpiece is positioned to the satisfaction of the operator, the 
foot switch 120 is then depressed and held down. This actuates the 
actuator 62 to cycle the arm 14 and move the punch 26 through the 
workpiece to the bottom of stroke position. In a manner analogous to the 
above-described notching operation, the bottom of stroke position 
corresponds to a previously set value in the final register 96. The final 
register position, or bottom of stroke position, can be preset by the 
machine manufacturer or can be set by the operator as described above with 
respect to the notching operation. 
When the signal from the encoder 64 matches the final register value, PLC 
88 generates a control signal which reverses the direction of travel of 
actuator 62, and the punch 26 is raised back toward the top of stroke 
position. However, the punch 26 continues to retract beyond the top of 
stroke position, as illustrated in FIG. 6, to strip the workpiece from the 
punch 26. In a preferred operational sequence, the punch retracts about 
0.25 inches beyond the top of stroke position. This momentary, additional 
retraction of the punch 26 can be effected by a previously programmed 
sequence in the PLC 88. When the encoder signal first equals the value in 
the initial register 95, the PLC 88 continues operation of the actuator 62 
for a predetermined additional encoder signal value equivalent to about 
0.25 inches of travel. Then the PLC reverses the actuator 62 until the 
encoder signal value equals the initial register value, thus lowering the 
punch 26 to the top of stroke position, and the PLC 88 then terminates the 
operation of the actuator 64. The system is then ready for the next 
punching operation. 
Again, the initial register position or top of stroke position can be reset 
using the jog switch controls. 
Auto Mode Punching Operation 
The auto mode punching operation is used when a workpiece is positioned on 
a table using stops (not shown) or other means. As with spot mode 
punching, the punch 26 extends beyond the stripper 30 during punching and 
retracts within the stripper 30 subsequent thereto to ensure the removal 
or stripping of the workpiece from the punch. 
The machine operates in this mode with the punch 26 initially positioned 
above the stripper 30. Generally, the punch 26 is cycled fully to punch 
the workpiece and return above the stripper (to strip the workpiece) where 
it remains until the next punch cycle. 
If the main power switch 87 had been turned off, then the machine must be 
initially run through the reference sequence operation as explained above 
in detail relative to the "Notching Operation." If the main power switch 
87 had not been turned off following a prior operation, then the reference 
sequence need not be repeated. 
When the reference sequence has been established, the tool selector mode 
switch 90 is set to "AUTO-PUNCH," and the notcher guard must be in place 
(closed). Then the workpiece is positioned in the punching station 22, and 
the stripper 30 is adjusted to the lowest possible position. 
Then the jog switch 106 is operated to position the punch 26 to an 
elevation just above the stripper 30 (e.g., about 0.25 inch above the 
stripper 30). This is a top of stroke position, and the encoder signal 
value for this top of stroke position is automatically stored in the 
initial register 95 in the PLC 88 upon release of the jog switch 106. The 
workpiece position can then be further adjusted with the table stops or by 
hand. 
The foot switch 120 is then depressed and held down. This operates the 
actuator 62 to cycle the punch 26 through the workpiece to the bottom of 
stroke position. Failure to hold the foot switch 120 down until the bottom 
of stroke is reached will cause the punch to return to the top of stroke 
position. 
When the bottom of stroke position is reached, the signal from the encoder 
64 equals a preset, stored value in the final register 96. In response to 
this condition, the PLC 88 generates a control signal which reverses the 
direction of travel of the actuator 62 and the punch 26. (The foot switch 
120 can then be released, if desired.) Upon reaching the top of stroke 
position, the punch is free of the workpiece which as has been stripped by 
the stripper 30. The signal from the encoder 64 matches the stored value 
in the initial register 95 when the punch is at the top of stroke 
position. At that point, the PLC 88 generates a second signal which stops 
the actuator 62. The punch 26 then remains at this initial, or top of 
stroke, position above the stripper. 
As with the other modes of operation, the top of stroke position can be 
reset in the register 95 at any time using the jog switches; and, the 
bottom of stroke position may be preset by the machine manufacturer or may 
be set by the operator. 
Although the embodiment shown and described herein discloses the use of a 
pulse generator rotary encoder 64 to sense the position of the pivoting 
beam arm 14, it will be readily appreciated by those skilled in the art 
that alternative embodiments of the present invention could employ other 
digital encoders or even analog sensing devices, such as potentiometers, 
to sense the arm position and generate position signals corresponding to 
the sensed arm position. 
As will be readily understood by those skilled in the art, the novel 
concepts of the present invention provide numerous advantages over the 
prior art machine tool stroke control systems presently in use in the 
industry. One such advantage is that the present system does not utilize 
limit switches to sense the arm position or to control arm operation. 
Thus, because no limit switches are used, the maintenance and adjustment 
of such switches is eliminated. This represents a significant time savings 
in the manufacture and maintenance of the machine. 
Moreover, unlike the prior art control systems which employ limit switches 
and sense arm position only at specific locations according to the 
installed positions of such limit switches, the present invention can 
provide continuous sensing of the arm positions over the entire range of 
travel. 
Furthermore, the flexibility of the preferred PLC programming and control 
can increase the efficiency and overall operation of the machine. 
It will be readily apparent from the foregoing detailed description of the 
invention and from the illustrations thereof that numerous variations and 
modifications may be effected without departing from the true spirit and 
scope of the novel concepts or principles of this invention.