DUAL FORCE RAM DRIVE FOR A SCREW PRESS

ENTRAINEMENT DE BELIER DOUBLE FORCE POUR PRESSE A VIS

English Abstract

Precise motion of the ram of a fastener press is controlled by high torque and
low torque
motors for high speed/low force and high force pressing of the ram by the ram,
respectively. The
high torque motor means drive passes through a bidirectional overrunning
clutch. The clutch is
controlled by the relative motion of the two separate motor drive speeds of
which are regulated
by a controller. The clutching motion is therefore controlled only by the
relative speed of its
drive versus driven components. This provides an extremely smooth and
responsive transition
between high speed/low force and low speed/high force operation of the ram so
that the pressing
cycle can be as fast and efficient as possible.

French Abstract

Le mouvement précis du vérin d'une presse de fixation est commandé par des moteurs à couples élevés et à faibles couples pour une pression à grande vitesse/faible force et force élevée du vérin par le vérin, respectivement. L'entraînement du moteur à couple élevé passe par un embrayage à roue libre bidirectionnel. L'embrayage est commandé par le mouvement relatif des vitesses d'entraînement des deux moteurs séparés, qui sont régulées par un contrôleur. Le mouvement d'embrayage est par conséquent commandé uniquement par la vitesse relative de son entraînement par rapport aux composants entraînés. Ceci permet une transition extrêmement douce et réactive entre un fonctionnement à grande vitesse/faible force et à basse vitesse/grande force du vérin, si bien que le cycle de pressage peut être aussi rapide et efficace que possible.

Claims

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CLAIMS:
1. A drive for a ram press, comprising:
a frame;
screw drive means mounted to said frame, said drive means being selectively
rotatable in
opposite directions by first motor means;
a ram mounted to said screw drive reciprocal in a range of motion between
extended and
retracted positions;
second motor means connected to said screw drive means for rotation thereof;
a bidirectional,-self-disengaging clutch having an input shaft connected to
said second
motor means and an output shaft connected to said screw drive means whereby
the clutch
disengages whenever said output shaft is driven at a speed greater than the
speed of input shaft;
and
a programmable logic control system for regulating the position of the ram by
operation
of said first motor means and said second motor means whereby said first motor
means is
signaled to rotate said screw drive at a higher rate of speed relative to said
second motor means
during a fast movement phase of moving said ram, said clutch being disengaged
thereby.
2. The drive of claim 1 wherein said clutch is engaged when said control
system signals
said first motor to operate at a speed less than said second motor means
whereupon said ram is
moved by said second motor means during a high force phase of moving said
ram..
3. The drive of claim 1 further including means for sensing the position of
said ram
electrically connected to said logic control system.
4. The drive of claim 1 wherein said first motor means is a high speed low
torque motor and
said second motor means comprises a gear reducer interposed between said
second motor means
and the input shaft of said clutch whereby said clutch input shaft is driven
at a high torque and a
low speed.
5. The drive of claim 1 wherein both first and second motor means always
rotate said drive
screw in the same direction when both motor means are simultaneously
operative.

Description

CA 02695160 2010-03-08
DUAL FORCE RAM DRIVE FOR A SCREW PRESS
RELATED APPLICATION
This patent application is related to provisional patent application serial
number
60/972,436 entitled "Setup System for a Fastener Press" filed on September 14,
2007 and
provisional patent application serial number 60/972,447 entitled "Dual Force
Ram Drive for
a Screw Press" filed on September 14, 2007, priority from which is hereby
claimed.
FIELD OF THE INVENTION
This invention relates to a fastener press which utilizes electric servo
motors for
precise ram position control. More specifically, the present invention relates
to a servo motor
driven ram having separate high-force and low-force drive motors using a
clutch-type drive
mechanism and regulated by a controller.
BACKGROUND OF THE INVENTION
The desirable characteristics of a fastener insertion press are high speed and
high
force. To achieve these characteristics a single drive unit is impractical as
high cost, large
power requirements, and large physical size are restrictions. However, a press
motion
profile with a high speed approach to the pressing position and then an
insertion press to a
high force at slower speeds provides a solution.
To achieve this motion profile, presses utilize a two-motor servo system to
control
velocity, position, and force of the press ram to install fasteners to the
proper force or
distance depending on the application. A high torque drive is engaged to drive
the ram to the
desired force or position. After insertion the high speed motor returns the
ram to the home
position.
There is therefore a need in the art for a ram drive in a press which provides
both high
speed and high force accurately and reliably. There is a further need for an
accurate and
reliable ram drive and press which is economical to manufacture and does not
require
significant operator skill.
SUMMARY OF THE INVENTION
In order to meet the needs of the art described above, the present invention
has been
devised. A fastener press, for example a Pemserter Series 3000 manufactured
and sold by
Penn Engineering and Manufacturing Corp., as shown in Figure 1, utilizes a
bidirectional
over-running clutch through which high force ram drive power passes. The
clutch is
controlled by relative motion of two separate motor drives as will be
described in detail

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below. Bidirectional over-running clutches are commercially available
components that
consist of a regular, polygon-shaped inner hub surrounded by rollers encased
in an outer hub
as shown in Figure 3. The inner and outer hubs are connected to separate
shafts. The inner
hub shaft can derive the outer hub shaft in either a clockwise or
counterclockwise direction if
the inner hub shaft speed of rotation is greater than the outer hub. If the
outer hub speed is
greater than the inner hub then the clutch is disengaged and the outer hub can
rotate
independently of the inner hub. The clutching action is therefore controlled
only by the
relative speed of its drive versus driven components. This provides an
extremely smooth and
responsive transition between high speed/low force and low speed/high force
operation of the
ram so that the pressing cycle can be as fast and efficient as possible. These
structures may be
used with the setup system for a fastener press disclosed in provisional
patent application
serial no. 60/972,436 of the same Applicant.
According to an aspect of the present invention, there is provided a drive for
a
ram press, comprising: a frame; screw drive means mounted to said frame, said
drive means
being selectively rotatable in opposite directions by first motor means; a ram
mounted to said
screw drive reciprocal in a range of motion between extended and retracted
positions; second
motor means connected to said screw drive means for rotation thereof; a
bidirectional, self-
disengaging clutch having an input shaft connected to said second motor means
and an output
shaft connected to said screw drive means whereby the clutch disengages
whenever said
output shaft is driven at a speed greater than the speed of input shaft; and a
programmable
logic control system for regulating the position of the ram by operation of
said first motor
means and said second motor means whereby said first motor means is signaled
to rotate said
screw drive at a higher rate of speed relative to said second motor means
during a fast
movement phase of moving said ram, said clutch being disengaged thereby.
Before explaining at least one embodiment of the invention in detail, it is to
be
understood that the invention is not limited in its application to the details
of construction and
to the arrangements of the components set forth in the following description
or illustrated in
the drawings. The invention is capable of other embodiments and of being
practiced and

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carried out in various ways. Also, it is to be understood that the phraseology
and terminology
employed herein are for the purpose of description and should not be regarded
as limiting.
As such, those skilled in the art will appreciate that the conception, upon
which
this disclosure is based, may readily by utilized as a basis for the designing
of other structures,
methods, and systems for carrying out the several purposes of the present
invention. It is
important, therefore, that the claims be regarded as including such equivalent
constructions
insofar as they do not depart from the spirit and scope of the present
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a front left isometric view of a ram press utilizing the
invention.
Figure 2 is a diagram showing the major components of the invention.
Figure 3 is a top front left isometric view of the bidirectional clutch of the
invention.
Figure 4 is a elevation cross-sectional view of the bidirectional clutch of
the
invention.
1 5 Figure 5 is a graph showing the pressing profile of one embodiment
of the
invention depicting the speed of the ram over time.

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DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to Figure 1, a ram press 4 employing the invention is shown
which
includes a c-shaped frame 1 that supports an anvil 2 that is reciprocally
impacted by ram 3.
Referring now to Figure 2, major components of the invention are disclosed
which
comprise a frame that supports basic mechanical components of the invention
that comprise a
high-speed mechanical actuator and a high-torque motor. Also supported by the
frame, is a
screw drive which may be operated in either direction by either the high-speed
or low-speed
motor means. A bidirectional self-disengaging clutch is connected to the high
torque motor
means which includes a motor/gear reducer combination. A programmable logic
controller
regulates operation of the two motors and thus movement of the ram by way of
the screw
drive. The bidirectional clutch is connected to the main shaft of the screw
drive by way of a
timing belt. The logic controller regulates the movement of the ram according
to a pressing
profile that will be described in more particularity with regard to Figure 5.
With continued reference to Figure 2, the press ram is moved by a screw
actuator
whose shaft is coupled directly to the high speed motor means in this
embodiment being the
commercially available device generally referred to as an electromechanical
actuator. The
device incorporates a screw drive mechanism so that its internal shaft is
reciprocated in a
range of motion between extended and retracted positions. That drive shaft is
also coupled to
the output of the above-described clutch by way of a gear belt drive. The
input shaft of the
clutch is coupled to the high torque motor. The clutch is operated by the
relative speeds of
separate brushless DC or AC servo motors that are regulated by a controller.
Each motor has
a feedback device such as an encoder or resolver and an additional encoder is
attached to the
main actuator shaft so that the relative position of the ram is known
regardless of which
motor is operating the ram. One motor provides a high-speed drive while the
second motor is
a high-torque drive which is an integrated servo gear motor with a 10 to 1
ratio. The. high-
torque motor means has its own encoder for communication and control and its
output shaft
is coupled to the high-speed motor's drive shaft through the above-described
high-torque
clutch, transmitted there by a belt. The high-torque motor can rotate the
screw actuator when
the clutch is engaged. Engagement of the clutch is achieved by regulating the
speeds of the
motors to switch ram operation from one motor to the other when the other is
running faster.
Referring now to Figures 3 and 4, the bidirectional clutch of the invention is
a
commercially available device well known in the mechanical arts. Figure 4 is a
cross-

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sectional view of the bidirectional clutch describing greater details of its
structure.
Power is transmitted by rollers 45 between the inner hub 43 and the outer hub
shown in Figure 4. The
= outer hub 40 includes shaft 41 that carries the output of the clutch and
is connected to the high speed
= motor by way of a belt drive as depicted in Figure 2. The inner hub 43
includes output shaft 44 which
is connected to the high torque output of the gear motor.
The required movements of the ram can be described by four stages:
1. High-speed down for set up or up for home position; =
2. Upward=high-speed movement after any move not requiring high-force;
3. High-force pressing; and
= 4. =Upward movement after high force pressing
One embodiment of the invention may be described in detail as follows. The
four
stages of movement required of the ram described above are specifically
carried out in the
following steps for each movement, as follows:
=
1. Sequence to move high speed axis down for setup and up to
home position
a. Enable high speed servo drive, it will hold position
b. Enable high torque
c. Bump high torque axis +.015" to ensure clutch is free
= d. .050 seconds into the move, enable high speed
axis
e. Run high speed axis down while high torque is finishing
its move
f. Disable high torque =
2. Sequence to move high speed axis up after any move not
requiring the high torque
axis for force: =
a. High speed is enabled, since it just ran down
b. = Enable high-torque
c. Bump high torque axis -.015" to ensure clutch is free
d. .050 seoonds in to the move, enable high speed axis
e. Run high speed axis up while high torque is finishing its move
f. = Disable high torque
3. Sequence to engage the clutch for pressing with the high
torque axis:
a. =Enable high speed servo drive ¨ it will hold position
b. Enable high torque
c. Bump high torque axis +.015 to ensure clutch is free

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d. High speed axis is moving down, two moves are compounded together
(registration move and collapse move)
e. Logical decisions are made on the fly to ensure the ram sensor tripped
within a
proper window and other conditions were satisfied
f. While high speed axis is moving, enable high torque
g. Start high torque axis moving approximately .650" above
workpiece -- it is
running at a slower speed than the high speed axis, so ram is still being
driven
at 8 IPS by high speed axis while high torque is turning at a speed
significantly less than this speed (.80 - 1.6 IPS)
h. High torque takes over ram movement as high speed axis is decelerating
to
zero
i. High speed axis finishes its move and disables
j. Run high torque axis down to complete pressing based on strain guage
input
4. Sequence to disengage the clutch after pressing with the high
torque axis:
a. After high torque axis completes all pressing and dwell, calculate
disengage
distance based on the force, to unload the force exerted on the clutch which
would cause back driving of the ram.
b. Move high torque axis -.XXX distance = (Force/16000)*-0.150
c. Keep high torque enabled
d. Re-enable high speed axis
The above movements are regulated by a controller which determines the speeds
of
the high speed and high torque motors which, in combination with the clutch of
Figure 2
interposed between the high torque motor and the screw actuator, follows a
prescribed
pressing profile that determines the motion of the ram.
Figure 5 represents a typical pressing profile. The X axis represents time in
seconds
and the Y axis represents speed (inches per second) The dotted lines 9
indicate the typical
motion of the high torque motor and the solid lines 8 represent the motion of
the high speed
motor as it relates to ram movement. At the beginning of the process the first
move is to start
the high torque motor prior to starting the high speed motor. This move
insures that the
clutch will disengage when the high speed motor overtakes the high torque
motor. When the
solid line crosses the dotted line (reading from left to right) the high speed
motor overtakes
the high torque motor and is then in control of the ram. The high torque motor
then

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decelerates and stops during the high speed move. At the mid point of the
graph the high
speed move (solid line) is approaching the pressing position. At this time the
high torque
motor starts accelerating while the high speed motor is decelerating. When the
dotted line
overtakes the solid line the high torque motor is in control and the pressing
sequence begins.
Once pressing is complete the high torque motor decelerates. On the return
stoke after
pressing, the high torque motor is started in reverse and begins to
accelerate. The high speed
motor then starts and begins to accelerate at a faster rate. When the solid
line crosses the
dotted line the high speed motor overtakes the high torque motor and is in
control. The high
speed motor finishes the move and decelerates to a stop. The cycle is complete
and ready for
the next cycle.
Therefore, the foregoing is considered as illustrative only of the principles
of the
invention. Further, since numerous modifications and changes will readily
occur to those
skilled in the art, it is not desired to limit the invention to the exact
construction and
operation shown and described, and accordingly, all suitable modifications and
equivalents
may be resorted to, falling within the scope of the invention.
,