Screwing tool for printing presses

A control system for a reversible screwing tool for tightening and loosening screws in a printing press or the like which includes a pair of angularly spaced pick-up devices coupled to the shaft of the tool for generating respective series of impulses. Monostable pulse generators are coupled to the respective pick-up devices, the generator coupled to the pick-up device in leading position, for counterclockwise rotation, being set to produce an output pulse which is substantially wider than that produced by the generator which is connected to the pick-up device in trailing position so that during counterclockwise rotation the output pulses from the generators timingly overlap one another. The generators feed into the input terminals of an AND gate which is, in turn, connected to a counter which counts the pulses resulting from counterclockwise rotation of the shaft. A relay interposed between the source and the tool automatically turns off the tool when a predetermined count is achieved thereby insuring that the screw is not excessively unscrewed from its tight condition. The relay is resettable in readiness for engagement of the succeeding screw. In the preferred embodiment of the invention the generator which is coupled to the pick-up device in leading position is responsive to the trailing edge of the received impulse while the generator connected to the pick-up device in trailing position is responsive to the leading edge of the pulse which it receives.

Power driven hand tools have been widely used for tightening of a screw 
with predetermined torque and for loosening the screw with percussive 
action followed by unscrewing at a high rotary speed. 
In the operation of a printing press, screws, and nuts as well, must be 
repeatedly tightened and loosened. In installing a set of printing plates 
for example the screws which hold the plate clamping bars are screwed 
tight by a power tool which is subsequently used, with reverse rotation, 
for loosening the screws for changing of the plates. 
It is an object of the invention to provide a control system for a 
reversible screwing tool which includes provision for automatic turn-off 
after the drive shaft undergoes a predetermined number of revolutions in 
the counterclockwise direction, the predetermined rotation being 
sufficiently limited to insure that the screw is only partially unscrewed 
from its tight condition. As a result, each screw will be loosened, and 
unscrewed, an amount sufficient to free the engaged plate clamping bar 
while still keeping the screw head below the periphery of the plate 
cylinder. Thus it is an object to provide a screwing tool for use on a 
printing press which is incapable of unscrewing a clamping screw to the 
extent that the head of the screw might, if inadvertently left 
untightened, damage the blanket and form rollers. It is a related object 
to provide a tool and control system therefor which is capable of 
unscrewing a series of clamping screws to a precise and safe degree in 
quick succession thereby permitting changing of a set of plates in the 
shortest possible time without exercise of particular care or attention. 
It is another object of the invention to provide a control system for a 
screwing tool which is capable of use with a wide variety of tools either 
electrically or penumatically driven and either of the direct drive or 
impact type. It is a more specific object, in such a system, to provide 
means for disabling the count during the period that the screw is being 
initially twisted loose and for enabling the count during the time that 
the screw is actually being unscrewed, thereby making the device 
particularly well suited for use with certain tools having an impact or 
percussion feature. 
It is a general object of the invention to provide a control system for a 
screwing tool which is not only reliable and easy to use but which is 
economical and capable of use with tools available on the commercial 
market, requiring only a minor modification of the tool structure.

While the invention has been described in connection with a preferred 
embodiment, it will be understood that we do not intend to be limited to 
the particular embodiment shown but intend, on the contrary, to cover the 
various alternative and equivalent constructions and circuitry included 
within the spirit and scope of the appended claims. 
Turning now to FIG. 1 there is shown a screwing tool 10 which may either be 
of the pneumatic or electric type having a supply line 11 and an output 
shaft 12 carrying, at its end, a fitting 13. The body of the tool has a 
hand grip 14 providing a conveniently located set of controls 15 for 
clockwise and counterclockwise rotation. The controls are shown in the 
form of alternatively energizeable triggers, but it will be understood 
that a single trigger may be employed in conjunction with a direction 
selector switch, as may be commercially available. 
In the normal operation of the tool torque is applied to the screw in the 
clockwise direction for screwing it tight to a preselected torque level. 
Removal is obtained by rotation in the opposite direction, with impact or 
percussive means, not shown but indicated generally at 16, providing a 
high initial twisting force. 
In accordance with the present invention a pick-up device coupled to the 
shaft of the tool is provided for generating a series of pulses in 
accordance with rotation of the shaft in the counterclockwise direction 
with means for shutting off the tool after a predetermined count has been 
achieved thereby to insure that the screw is only partly unscrewed from 
its tight condition. More particularly in accordance with the invention a 
pair of angularly spaced pick-up devices are provided in the tool, one of 
which is in leading position during counterclockwise rotation, the pick-up 
devices being connected to monostable pulse generators. The generator 
which is coupled to the pick-up device in leading position is set to 
produce an output pulse which is substantially wider than that produced by 
the remaining generator so that during counterclockwise rotation the 
output pulses from the generators timingly overlap one another. An AND 
gate connected to the generators is responsive to the condition of 
overlap, the AND gate feeding a counter which effectively counts the 
counterclockwise revolutions of the drive shaft. The counter is used to 
control a relay interposed between the tool and its source for 
de-energizing the tool when the predetermined count is reached, the relay 
having provision for resetting in readiness for engagement of a succeeding 
screw. 
Mounted within the tool for rotation with the drive shaft 12 is a star 
wheel 20 with cooperating magnetic pick-up devices 21, 22 which are 
angularly spaced from one another. The star wheel has magnetic arms or 
rays which sweep the vicinity of the pick-up devices, the pick-up device 
21 being in "leading" position, and the device 22 being in "trailing" 
position during counterclockwise rotation of the star wheel. The pick-up 
devices will be understood, in the present instance, to be in the form of 
small magnetic pick-up coils but it will be apparent to one skilled in the 
art as the discussion proceeds that other equivalent types of pick-up 
devices may be used with equal advantage. 
The pick-up device 20 is connected to a preamplifier 25 which feeds an 
amplifier 26 (which is connected as an inverter for reasons to be 
described) and which in turn is connected to a monostable pulse generator 
30 having an input terminal 31 and an output terminal 32. The function of 
the pulse generator 30 is to receive an amplified impulse from the pick-up 
device 21 and to produce therefrom a well defined square wave pulse of 
predetermined amplitude and duration, or length. While monostable pulse 
generators are per se well known in the art, reference may be made to FIG. 
2a which shows a typical circuit. For convenience and economy the circuit 
may largely consist of an integrated circuit 33, a typical circuit for 
such usage, capable of being triggered by a negative-going voltage, is 
identified as Model DCL8162 Monostable Multivibrator manufactured by 
Signetics Corporation of Sunnyvale, California, U.S.A. For the purpose of 
adjusting the length of the resulting output pulse an RC circuit is used 
consisting of an adjustable rheostat 34 and capacitor 35. 
In the upper leg of the circuit, the pick-up device 22 is connected to a 
preamplifier 45 which feeds an amplifier 46 which in turn supplies a 
monostable pulse generator 50 having terminals 51, 52 and which may employ 
the same circuit as that shown in FIG. 2a. 
The pulse generators are connected to an AND gate 60 having input terminals 
61, 62 and an output terminal 63, the purpose of the AND gate being to 
produce an output pulse whenever pulses are simultaneously applied to the 
input terminals, that is, whenever the pulses applied to the input 
terminals are in timingly overlapped relation. 
The pulses from the AND gate are fed to an adjustable counter 70 having an 
input terminal 71 and an output terminal 72 and of the type, well known in 
the market, which produces an output signal when a predetermined count has 
been achieved, the count being adjustable by a control 73. The counter is 
preferably of the type which automatically resets itself incident to 
producing an output signal. 
The counter signal is fed to a disconnect relay 80 having an input 81, an 
output 82 and a reset terminal 83, the relay being of the normally closed 
type providing drop-out on receipt of an input signal. The relay is 
connected to a solenoid 90 which controls a valve 91 interposed in the 
supply line 11 between the source and the tool, assuming the tool is of 
the pneumatic type. Where the tool is electrically operated, the output 
circuit of the relay may be directly interposed in the electric supply 
line. 
For the purpose of resetting the relay a timer 100 is provided having an 
input terminal 101 and an output terminal 120. The timer, of a type 
commercially available, is so constructed that when an input signal is 
received at the input terminal an output signal occurs at the output 
terminal a predetermined time interval thereafter for the purpose of 
resetting the relay to its normally closed condition. The time interval is 
sufficient to enable the operator to release the trigger and remove the 
tool from the screw in readiness for engagement of a succeeding screw. 
In carrying out the present invention the monostable pulse generators 30, 
50 are differentially adjusted, by appropriate setting of the resistor 34 
therein, so that the pulse produced by the generator 30, which is 
connected to the pick-up 21, which is in leading position for 
counterclockwise rotation, is substantially longer than the pulse produced 
by the generator 50 in the trailing leg of the circuit. Moreover, in 
carrying out the invention in its preferred form the generator 30 is made 
responsive to the trailing edge of the impulse produced by the pick-up 21 
whereas the generator 50 is connected to be responsive to the leading edge 
of the pulse which it receives. Selective response to the trailing edge by 
the generator 30 may be obtained by connecting the amplifier 26, which 
feeds it, as an inverter. 
A typical cycle, achieving automatic de-energization of the tool upon a 
predetermined number of rotations of the shaft in a counterclockwise 
direction is as follows: Referring to FIG. 3a, counterclockwise rotation 
of the star wheel produces a series of impulses from the "leading" pick-up 
device 21 as indicated at A. A similar series of impulses are produced by 
the pick-up device 22 as indicated at B, the impulses A being of leading 
phase. Such impulses, fed to the pulse generators 30, 50 produce output 
pulses therefrom shown at C and D, which output pulses are fed to the AND 
gate 60. In accordance with the invention, the generator output pulses 
from the generator 30, triggered by the pick-up device 21 in "leading" 
position (during counterclockwise rotation) are artificially lengthened by 
appropriate adjustment of the rheostat 34 so that, during counterclockwise 
rotation, the pulses C and D are fed to the AND gate 60 in timingly 
overlapped relation resulting in creation of output pulses E at the output 
of the AND gate. 
Such gate output pulses are applied to the counter 70 which produces an 
output signal when a predetermined low count has been achieved, the output 
signal causing drop-out of the disconnect relay 80 and the opening of the 
valve 91 which supplies the tool, thereby turning off the tool outside of 
the operator's control after the screw has been loosened but before it has 
been excessively unscrewed. There is no limit to the "lowness" of the 
count; a count even as low as 1 may be utilized as a limiting condition 
where only a very slight amount of unscrewing is desired. 
When the tool turns off, the operator releases the control 15 and moves the 
tool to the next screw in the series. The timer 100 resets the relay 80 
within a short time interval so that the operator can manually re-energize 
the tool for unscrewing of the next screw in the series. 
Thus, employing the present invention, the tool can be moved quickly from 
one screw to the next, with the tool being manually turned on at each 
screw but automatically turned off, outside of the operator's control, 
when the screw has been loosened, that is, unscrewed, to just the right 
degree for plate replacement purposes. This insures that the screw, in its 
unscrewed state, is still below the profile of the plate so that, if a 
press operator should inadvertently fail to retighten one of the screws, 
such screw will not damage the form rollers or blanket cylinder. 
By causing the pulse generator 30 to respond to the trailing edge of an 
input pulse and the generator 50 to respond to the leading edge it will be 
apparent, in FIG. 3a, that only a limited amount of widening of pulses C 
is effective to produce overlap for a given angular spacing of the pick-up 
devices 21, 22. 
Referring next to FIG. 3b, it will be observed that the circuitry is 
effectively disabled during clockwise rotation of the tool, that is, 
during inward screwing of the screws to tight condition. Under such 
circumstances the pick-up device 22 occupies the "leading" position and 
the pick-up device 21 occupies the relatively "trailing" position so that 
the phase relationship of the pulses A and B are reversed. This causes a 
spreading apart of the output pulses from the generators 30, 50 resulting 
in lack of timed overlap so that pulses are not applied simultaneously to 
the AND gate, thereby avoiding creation of pulses E and effectively 
disabling the counter 70 and relay 80. 
However, in accordance with one of the more detailed aspects of the present 
invention, means are provided for counting revolutions in the 
counterclockwise direction only when the tool is rotated at normal 
unscrewing speed. This feature is useful in certain types of impact tools 
in which rotation of the shaft of the tool, to which the star wheel is 
connected, results in successive impacts being applied to the screw, at a 
slow shaft speed, for initially twisting the screw loose and prior to the 
tool's achieving normal unscrewing speed. The effective disablement of the 
counter at slow clockwise speed may be understood by comparing FIG. 3c 
with FIG. 3a previously discussed. In FIG. 3a, it will be recalled, 
alinement of the C and D pulses resulting from the pick-ups 21, 22, 
respectively, resulted in counting pulses E. However, at slow initial 
twisting speed the pulses A and B from the pick-ups are expanded on a time 
scale so that the resulting generator pulses C and D, instead of being 
aligned, are separated, in time, by an amount S so that the AND gate 60 is 
non-responsive. This enables utilization of the initial tool rotations for 
the purpose of impact "starting" of the screw head without including such 
rotations in the actual count. However, it should be noted that where the 
control system is employed with a direct drive tool, that is, a tool in 
which the motor is directly connected to the screw fitting, there is no 
loss of count as a practical matter since the screw head, once started, 
comes up quickly to normal tool speed. In any event loss of count by 
reason of low tool speed may be optionally prevented simply by adjusting 
the resistor 34, in the generator 30, to produce a somewhat more elongated 
output pulse. 
While the invention has been described in connection with a preferred 
embodiment it will be apparent that the invention in its broader aspects 
includes means coupled to the shaft of the tool for generating a 
distinctive series of pulses (pulses A and B in FIGS. 3a, 3b, 
respectively) depending upon whether the shaft is turning in the clockwise 
or counterclockwise direction, with a counter being provided having means 
(here the generators and AND gate) for making the counter selectively 
responsive to the series of pulses corresponding to counterclockwise 
rotation. 
While the invention preferably utilizes a commercial form of counter 
capable of making an actual count of the impulses from the AND gate, it 
will be understood that the term "counter" as used herein is used in the 
broad sense of an integrating device. Thus it will be apparent to one 
skilled in the art that the counter 70 may, if desired, and in its 
simplest aspect, be in the form of a capacitor across which voltage is 
successively built up by addition of pulses E to a point of triggering 
operation of the disconnect relay 80, without departing from the present 
invention. 
Also while it is preferred to employ a commercial form of resettable 
normally closed relay, it will be understood that the term relay is not 
limited to a device of the magnetic type and solid-state relay circuitry 
may be readily used. 
The term "trigger" has been used in reference to the manipulated control on 
the tool itself, but it will be understood that the manipulated control 
need not be of trigger shape or in trigger position to utilize the present 
invention. 
The invention has been particularly discussed in connection with operation 
of the screws on the clamping bars of a plate cylinder for changing of the 
plates, but it will be understood that the invention has other uses in the 
operation and adjustment of a press including the tightening and loosening 
of screws on the blanket cylinder when changing the blanket, the opening 
and closing of an ink fountain and the operation of the threaded adjusting 
means controlling the pressure between the plate and blanket cylinders. 
While the term "direct drive" has been contrasted with a drive of the 
impact type, it will be understood that both refer to tools in which the 
star wheel or equivalent rotation signalling device is directly connected 
to the fitting which engages the screw. The term "pulse generator" as used 
herein will be understood to include any device capable of producing a 
well defined pulse at the output upon being triggered by a pulse received 
by the input.