U.S. patent application number 09/773822 was filed with the patent office on 2001-06-28 for optical position monitor for knitting machines.
Invention is credited to Ganor, Zeev, Karasikov, Nir, Rafaeli, Izhak.
Application Number | 20010004839 09/773822 |
Document ID | / |
Family ID | 11061999 |
Filed Date | 2001-06-28 |
United States Patent
Application |
20010004839 |
Kind Code |
A1 |
Ganor, Zeev ; et
al. |
June 28, 2001 |
Optical position monitor for knitting machines
Abstract
An actuator system for activating a latch needle, which latch
needle has a shaft, comprising: a flat planar extension of said
shaft having first and second parallel planar surfaces; at least
one piezoelectric micromotor having a first surface region for
transmitting motion to a moveable element, which first surface
region is resiliently pressed to said first surface and at least
one additional piezoelectric motor having a second surface region
for transmitting motion to a moveable element which second surface
region is resiliently pressed to said second surface; and wherein
vibratory motions of said first and second surface regions apply
forces to said flat extension that cause motion in said latch
needle.
Inventors: |
Ganor, Zeev; (Herzelia,
IL) ; Rafaeli, Izhak; (Haifa, IL) ; Karasikov,
Nir; (Haifa, IL) |
Correspondence
Address: |
Wm Dippert
c/o Cowan, Liebowitz & Latman
1133 Avenue of the Americas
New York
NY
10036-6799
US
|
Family ID: |
11061999 |
Appl. No.: |
09/773822 |
Filed: |
February 1, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09773822 |
Feb 1, 2001 |
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09423939 |
Mar 27, 2000 |
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09423939 |
Mar 27, 2000 |
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PCT/IL98/00111 |
Mar 8, 1998 |
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Current U.S.
Class: |
66/111 |
Current CPC
Class: |
D04B 35/18 20130101;
D04B 15/78 20130101 |
Class at
Publication: |
66/111 |
International
Class: |
D04B 015/08 |
Claims
1. An actuator system for activating a latch needle, which latch
needle has a shaft, comprising: a flat planar extension of said
shaft having first and second parallel planar surfaces; at least
one piezoelectric micromotor having a first surface region for
transmitting motion to a moveable element, which first surface
region is resiliently pressed to said first surface and at least
one additional piezoelectric motor having a second surface region
for transmitting motion to a moveable element which second surface
region is resiliently pressed to said second surface; and wherein
vibratory motions of said first and second surface regions apply
forces to said flat extension that cause motion in said latch
needle.
2. An actuator system for activating a latch needle, which latch
needle has a thin flat shaft comprising: a flat planar extension of
said shaft having first and second planar surfaces; a piezoelectric
micromotor having a surface region for transmitting motion to a
moveable element; a transmission bracket for holding said
piezoelectric micromotor, said transmission bracket comprising a
bearing surface and a means for resiliently urging said surface
region of said piezoelectric micromotor towards said bearing
surface; and wherein said flat extension is inserted between said
surface region of said piezoelectric micromotor and said bearing or
said non-stick surface and wherein vibratory motion of said surface
region applies force to said flat extension causing motion in said
latch needle.
3. An actuator system according to claim 2 wherein said bearing
surface is the surface of a rotatable roller or ball.
4. An actuator system according to claim 2 wherein said bearing
surface is a surface having a low friction coating.
5. An actuator system for activating a latch needle, according to
claim 1 wherein said surface region for transmitting motion to a
moveable element comprises a wear resistant nub that makes contact
with a surface of said moveable element towards which said surface
region for transmitting motion is resiliently pressed in order to
transmit motion to said moveable element.
6. An actuator system for activating a latch needle, according to
claim 1 wherein points on surfaces of said flat extension at which
said surface regions of said piezoelectric micromotors make contact
are clad in wear resistant material.
7. An actuator system for activating a latch needle, according to
claim 2 wherein said surface region for transmitting motion to a
moveable element comprises a wear resistant nub that makes contact
with a surface of said moveable element towards which said surface
region for transmitting motion is resiliently pressed in order to
transmit motion to said moveable element.
8. An actuator system for activating a latch needle, according to
claim 2 wherein points on surfaces of said flat extension at which
said surface regions of said piezoelectric micromotors make contact
are clad in wear resistant material.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to knitting machines and in
particular to means and methods for activating latch needles in
knitting machines and monitoring latch needle positions.
BACKGROUND OF THE INVENTION
[0002] Automatic knitting machines use banks of large numbers of
closely spaced latch needles to interlock threads in a series of
connected loops to produce a knitted fabric. The latch needle is a
long flat needle having, at one end, a small hook and a latch that
swivels to open and close the hook. The hook ends of the latch
needles are moved forwards and backwards towards and away from the
threads being knitted into the fabric. As a latch needle is moved,
its latch alternately opens and closes so that the hook catches a
thread close to it, pulls it to create a loop of fabric, and then
releases the thread to start the cycle over again and produce
another loop of fabric.
[0003] Latch needles are arranged parallel to each other, in arrays
of many hundreds to thousands of latch needles in modem knitting
machines. The latch needles are placed into narrow latch needle
slots that are machined into a planar surface, hereafter referred
to as a "needle bed surface", of a large rectangular metal plate,
hereafter referred to as a "needle bed". The latch needle slots
hold the latch needles in position and confine their motion to
linear displacements along the lengths of the latch needle slots.
The latch needle slots are parallel to each other and equally
spaced one from the other with spacing that varies depending upon
the quality and type of fabric being produced. Spacing of two to
three millimeters is typical, but spacing significantly less than
and greater than two millimeters are also common.
[0004] The latch needle slots in a needle bed are sufficiently deep
so that all or most of the body of a latch needle lies completely
in the latch needle slot in which it is placed and below the needle
bed surface into which the latch needle slots are machined. A small
square fin that sticks out from one side of the shaft of the latch
needle protrudes above the needle bed surface. The fins of all
latch needles in a needle bed are accurately aligned in a single
straight row perpendicular to the latch needle slots.
[0005] The latch needles are moved, hereafter referred to as
"activated", back and forth in their respective latch needle slots
in order to form loops in a fabric being knitted, by a shuttle that
travels back and forth along the length of the needle bed surface
parallel to the row of aligned latch needle fins. The shuttle has a
flat planar surface facing and parallel to the needle bed surface
that extends the full length of the shuttle along the direction of
travel of the shuttle. The surface has a channel extending the fall
length of the shuttle along the direction of travel of the shuttle.
The channel is open at both of its two ends, and both ends are
aligned with the row of aligned fins. As the shuttle moves along
the row of latch needle fins, the fins of the latch needles
sequentially enter the channel at one end of the channel, travel
along the channel length and exit the channel at the other end of
the channel. For most of its length the channel is parallel to the
row of aligned fins, i.e. the direction of travel of the shuttle,
however towards its middle it has a bend. A latch needle is
activated when its fin encounters the bend and moves along the
direction of the bend. In moving along the direction of the bend,
the fin and its latch needle are moved back and forth along the
direction of the latch needle slot in which the latch needle is
placed, i.e. perpendicular to the row of aligned fins.
[0006] The conventional method for moving latch needles in a
knitting machine as described above has a number of drawbacks.
[0007] For one, the sequential activation of latch needles by a
shuttle as the shuttle moves along a needle bed limits the
production rates of fabrics. Production rates of fabric produced by
knitting machines could be increased if latch needles were
individually activated and different combinations of latch needles
could be moved simultaneously. Some shuttles in fact have more than
one channel in order to simultaneously activate more than one latch
needle and increase production rate.
[0008] In addition, in the process of knitting a fabric, dust and
dirt accumulate in the slots in which latch needles of a knitting
machine move. As the dust and dirt accumulate, more force is
required to move the latch needles. At some point, dust and dirt
accumulate to such an extent that a latch needle jams in its slot.
The shuttle is too massive and moves too quickly for it to be
practical for the shuttle to be sensitive to, or respond to,
changes in the force needed to move a particular latch needle. As
the shuttle rushes along the needle bed and encounters a jammed
latch needle it breaks the fin or some other part of the jammed
latch needle. When this happens physical damage to the knitting
machine is often considerably more extensive than the damage to the
single latch needle that jammed and knitting machine down time as a
result of the damage is prolonged.
[0009] In order to prevent damage to knitting machines from jammed
latch needles it would be advantageous to have a system for moving
latch needles in a knitting machine that activates latch needles
individually and is responsive to changes in the forces required to
move individual latch needles.
[0010] Prior art direct needle drive systems exist that provide for
individual activation of latch needles in a knitting machine. These
systems, hereafter referred to as "DND" systems, generally provide
an actuator for each latch needle and a system for monitoring the
position of each latch needle. However, the prior art systems have
not been completely satisfactory. The dimensions of actuators used
in the prior art systems are large compared to the spacing between
latch needles. Complicated spatial configurations are therefore
required to pack large numbers of the actuators in a convenient
volume of space near to the latch needles in order to couple the
actuators to the latch needles.
[0011] Additionally, the response times of prior art DND systems
are slow. This is the result of slow response times of actuators
and of latch needle position monitoring systems used in these
systems. The advantages in production rate and decreased knitting
machine down time that should be provided by prior art DND systems
are at least partly neutralized by the slow response times of these
systems.
SUMMARY OF THE INVENTION
[0012] It is an object of one aspect of the present invention to
provide a knitting machine comprising a fast response time DND
system for activating latch needles in the knitting machine.
[0013] It is an object of another aspect of the present invention
to provide a DND system in which each latch needle of a knitting
machine is activated exclusively by at least one piezoelectric
micromotor which activates only that latch needle.
[0014] An object of another aspect of the present invention is to
provide a piezoelectric micromotor suitable for use in a fast
response time DND system.
[0015] An additional aspect of the present invention is to provide
a transmission for coupling each latch needle in a DND system, in
accordance with a preferred embodiment of the present invention, to
an at least one piezoelectric micromotor, which at least one
piezoelectric micromotor, hereafter referred to as "at least one
exclusive piezoelectric micromotor", is not coupled to any other
latch needle.
[0016] Piezoelectric micromotors can be made small and powerful and
response times of piezoelectric micromotors can satisfy the fast
response time requirements of modem knitting machines. The dynamic
range of motion available from piezoelectric micromotors and the
energy that can be transmitted in short periods of time from
piezoelectric micromotors to moveable elements are also consistent
with the requirements of modern knitting machines. A piezoelectric
micromotor and transmission, in accordance with preferred
embodiments of the present invention, can therefore be used to
provide fast response time activation of individual latch needles
in a knitting machine.
[0017] It is an object of yet another aspect of the present
invention to provide a DND system comprising a fast response time
system for monitoring the position of latch needles activated by
the DND system.
[0018] It is a further object of another aspect of the present
invention to provide an electro-optical latch needle position
monitoring system, hereafter referred to as an "OPM", that operates
with a fast response time.
[0019] DND systems by their nature require fast response time
position monitoring systems for monitoring the positions of latch
needles that they activate. The positions of the latch needles are
controlled in knitting machines to accuracy on the order of 25-50
micrometers (.mu.m). A DND system that moves latch needles with a
velocity "V" must therefore sample the position of each latch
needle it activates with a frequency of between
.about.2.times.(Vm/sec.div.25 .mu.m) to 2.times.(Vm/sec..div.50
.mu.m), in order to control the position the latch needle to an
accuracy of 25 .mu.m-50 .mu.m. It therefore requires a position
monitoring system with a response time on the order of (25 .mu.m-50
.mu.m)/2V. In many conventional knitting machines V is on the order
of 1.5 m/sec. A DND system that moves latch needles with this
velocity therefore requires a system that samples the position of
latch needles with a frequency, or sampling rate, of between 50-100
kHz and a response time between 10 .mu.sec and 20 .mu.sec.
[0020] Electro-optical systems inherently operate at frequencies
that are much faster than typical mechanical cycle frequencies of
motion of knitting machine components. In particular an
electro-optical OPM, in accordance with a preferred embodiment of
the present invention, can provide the fast response time and
accuracy of measurement required for monitoring latch needle
positions in DND systems.
[0021] A piezoelectric micromotor for operating individual latch
needles in a DND, in accordance with a preferred embodiment of the
present invention, comprises a ceramic vibrator formed in the shape
of a thin flat plate having two large planar surfaces and narrow
edge surfaces. Piezoelectric vibrators of this type are described
in U.S. Pat. No. 5,453,653, which is incorporated herein by
reference. The thickness of the vibrator preferably ranges from one
to a few millimeters. The thickness of the vibrator thus has
dimensions on the order of the size of the spacing between latch
needles in a needle bed. It is therefore possible to pack large
numbers of these vibrators close to each other with their large
planar surfaces parallel and with a thin edge of each vibrator
aligned with a single latch needle in the needle bed. Each latch
needle is activated (i.e. moved back and forth in its latch needle
slot in order to form a loop in a fabric being knitted) by coupling
to the latch needle vibratory motion of at least one exclusive
piezoelectric micromotor having a thin edge aligned with the latch
needle. Coupling of the latch needle and the vibratory motion of
the at least one exclusive piezoelectric motor may be accomplished
by means of a transmission, in accordance with a preferred
embodiment of the present invention.
[0022] In a DND, in accordance with a preferred embodiment of the
present invention, latch needles in a knitting machine needle bed
and piezoelectric micromotors are coupled by a rotary transmission
comprising a bearing shaft on which a plurality of annuli is
stacked. The annuli rotate freely on the bearing shaft. Each latch
needle in the knitting machine needle bed is coupled to vibratory
motion of a different at least one exclusive piezoelectric motor
via one of the plurality of annuli.
[0023] The bearing shaft is mounted over the needle bed, preferably
close to the needle bed and with its axis parallel to the needle
bed and perpendicular to the latch needle slots in the needle bed.
The spacing between the annuli on the shaft is such that the fin of
each latch needle in the needle bed is aligned with a different
annulus on the bearing shaft. A preferably rigid connecting arm
connects the fin of each latch needle in the needle bed to the
annulus with which the latch needle fin is aligned. The connecting
arm is attached to the fin, preferably by a slideable or flexible
joint, formed using methods known in the art.
[0024] Each annulus on the bearing shaft is coupled to its own at
least one exclusive piezoelectric micromotor, in accordance with a
preferred embodiment of the present invention by resiliently
pressing the at least one exclusive piezoelectric micromotor
against the annulus. Activation of the piezoelectric micromotors
coupled to an annulus causes the annulus to rotate. The rotation of
the annulus is transmitted to the fin of the latch needle to which
the annulus is connected, by the connecting arm. The joint
connecting the fin and the connecting arm translates the rotational
motion of the connecting arm to a linear motion of the latch needle
forwards and backwards in its latch needle slot parallel to the
length of the latch needle slot, thereby activating the needle.
[0025] In a DND system, in accordance with an alternative preferred
embodiment of the present invention latch needles in a knitting
machine needle bed and piezoelectric micromotors are coupled by a
linear transmission. With the linear transmission each latch needle
in a knitting machine needle bed has at least one exclusive
piezoelectric micromotor pressed, preferably by resilient force,
directly onto the shaft of the latch needle or onto a suitable
extension of the shaft of the latch needle. The latch needle slots
in which the latch needles are placed, and/or, the surfaces of the
needles in contact with the latch needle slots are preferably
provided with bearings or nonstick surfaces. This reduces the
possibility of a latch needle jamming or sticking in its latch
needle slot under the application of the resilient force pressing
the at least one exclusive piezoelectric micromotor to the latch
needle shaft or suitable extension thereof. Coupled in this way,
vibratory motion of the at least one exclusive micromotor pressed
to a latch needle shaft or extension thereof activates the latch
needle by causing the latch needle to move back and forth in its
latch needle slot.
[0026] In another form of linear transmission, in accordance with a
preferred embodiment of the present invention, piezoelectric
micromotors are coupled directly to a "coupling" fin of a latch
needle in order to transmit motion to the latch needle. The
coupling fin, except for its dimensions, is preferably similar in
shape and construction to conventional latch needle fins. The
coupling fin is a planar extension of the body of the latch needle
having first and second parallel planar sides and thin edges.
Preferably, the coupling fin is formed as an integral part of the
latch needle and lies in the plane of the body of the latch needle
(the latch needle is flat). A rectangular region of the first side
and a rectangular region of the second side, hereafter referred to
as first and second "coupling regions" respectively, are preferably
clad in wear resistant material suitable for friction coupling with
piezoelectric micromotors, such as for example, alumina.
Preferably, the first and second coupling regions are congruent and
directly opposite each other.
[0027] In one configuration for coupling piezoelectric micromotors
to the coupling fin, in accordance with a preferred embodiment of
the present invention, at least one micromotor is resiliently
pressed to each of the first and second coupling regions so that a
surface region of the micromotor used for transmitting motion from
the micromotor to a moveable element, or a hard wear resistant
friction nub on the surface region, contacts the coupling region.
Preferably, the same number of piezoelectric micromotors is
resiliently pressed to each of the first and second coupling
regions. Preferably the at least one micromotor pressed to the
first coupling region is identical to the at least one micromotor
pressed to the second coupling region. Preferably, points at which
the at least one micromotor pressed to the first coupling region
contacts the first coupling region and points at which the at least
one micromotor pressed to the second coupling region contacts the
second coupling region are directly opposite each other.
Preferably, the magnitude of the forces exerted on the coupling fin
perpendicular to the plane of the coupling fin by the at least one
micromotor pressed to the first and second coupling regions are
equal. Preferably, the at least one piezoelectric micromotor
pressed to each coupling region comprises one micromotor.
[0028] The latch needle is driven back and forth in its latch
needle slot when the at least one piezoelectric micromotor pressed
to the first and second coupling regions are activated so as to
transmit linear motion in the same direction to the coupling fin.
Preferably, the at least one piezoelectric micromotor pressed to
the first and second coupling regions are activated in phase. This
substantially prevents a torque that tends to twist the latch
needle in its latch needle slot from developing.
[0029] In another configuration for coupling piezoelectric
micromotors to the coupling fin, accordance with a preferred
embodiment of the present invention, a piezoelectric micromotor
coupled to a coupling fin is mounted in a transmission bracket. The
transmission bracket comprises a bearing or a non-stick surface
area against which a surface region of the micromotor used for
transmitting motion to a moveable element, or preferably, a wear
resistant friction nub on the surface region of the micromotor, is
resiliently pressed. In order to couple the piezoelectric
micromotor to the coupling fin, the coupling fin is inserted
between the friction nub and the bearing or the non-stick surface.
With this coupling configuration a single piezoelectric micromotor
can be used to activate a latch needle without causing unwanted
torque that twists the latch needle in its latch needle slot. Force
exerted by the piezoelectric micromotor perpendicular to the plane
of the coupling fin is opposed by an equal and opposite force
exerted on the coupling fin by the bearing or the non-stick
surface.
[0030] In order to couple adjacent latch needles in a needle bed to
piezoelectric micromotors using coupling fins, in accordance with a
preferred embodiment of the present invention, coupling fins of
adjacent latch needles are preferably displaced with respect to
each other in the direction of motion of the latch needles and/or
protrude different distances above the latch needle bed. This
provides sufficient space between piezoelectric micromotors coupled
to coupling fins of adjacent latch needles so that the
piezoelectric micromotors do not interfere with the motion of the
latch needles
[0031] A DND system controls latch needle actuators responsive to
the position of the particular latch needle to which the actuators
are coupled. In a DND system, in accordance with a preferred
embodiment of the present invention, latch needle positions are
monitored by an OPM.
[0032] An OPM, in accordance with a preferred embodiment of the
present invention, monitors the position of a latch needle by
optically tracking the position of a small light reflecting region,
or a region comprising areas of substantially different
reflectivity, such as a light reflecting region with a black line,
hereafter referred to as a "fiducial", located at a known fixed
position on the latch needle. The fiducial is illuminated by light
from an appropriately located light source, hereafter referred to
as a "fiducial illuminator". The fiducial reflects a portion of the
light from the fiducial illuminator with which it is illuminated
into an optical device, hereafter referred to as a "fiducial
imager", comprising a detector having a light sensitive surface.
The fiducial imager uses the reflected light to form an image of
the fiducial on the light sensitive surface of its detector. A
change in the position of the fiducial causes a change in the image
of the fiducial on the light sensitive surface, which change is
used to determine the change in position of the fiducial.
[0033] There are a number of other ways in which the latch needle
can be provided with a fiducial, in accordance with preferred
embodiments of the present invention. For example, a small
retro-reflector can be fixed to a point on the body of the latch
needle or an appropriate reflecting discontinuity, such as a
scratch or dimple, can be formed on a region of the surface of the
latch needle. Preferably, the fiducial reflects incident light
diffusely within a cone of half energy angle on the order of
10.degree.-20.degree.. The detector and fiducial illuminator
comprised in a fiducial imager, in accordance with a preferred
embodiment of the present invention, are located so that at any
position occupied by the latch needle in its operating range of
motion, substantially all the light reflected by the latch needle
fiducial into the half energy cone is incident on the detector.
[0034] In order to provide position measurements for a plurality of
latch needles in a needle bed of a knitting machine, an OPM, in
accordance with a preferred embodiment of the present invention,
comprises a plurality of fiducial imagers arranged in an array.
Preferably, the fiducial imagers are aligned collinearly in a line
array defined by an axis that is a straight line. Preferably, the
axis is parallel to the needle bed surface of the needle bed and
perpendicular to the directions of the needle bed slots.
[0035] The number of the plurality of fiducial imagers in the array
in a preferred embodiment of the present invention is preferably
equal to the number of the plurality of latch needles. Each
fiducial imager is aligned with a different one of the plurality of
latch needles and provides position data for the latch needle with
which it is aligned. The positions of all latch needles in the
plurality of latch needles are thus, preferably, simultaneously
measurable by the OPM. Preferably, the number of the plurality of
latch needles is equal to the number of latch needles in the
knitting machine.
[0036] In some preferred embodiments of the present invention, the
number of the plurality of fiducial imagers in the array of
fiducial imagers of an OPM is less than the number of the plurality
of latch needles whose positions are to be determined using the
OPM. In order to provide position measurements for all the latch
needles of the plurality of latch needles, the array of fiducial
imagers in the OPM is moved along the needle bed in which the latch
needles are held. Preferably, the array of fiducial imagers is
moved over the needle bed in a direction collinear with the axis of
the array.
[0037] In one preferred embodiment of the present invention the
fiducial imager comprises a lens and a detector having a light
sensitive surface that is divided into first and second regions.
The areas of the two regions are preferably equal and preferably
abut each other along a straight line. The straight line is
preferably oriented substantially perpendicular to the direction of
motion of the latch needle. The detector sends first and second
signals that are functions of the amounts of reflected light from
the fiducial incident on the first and second regions respectively
to a controller. The lens focuses reflected light from the fiducial
to form an image of the fiducial on the light sensitive surface of
the detector. The portions of the image, and thereby the amounts of
reflected light, that fall on the first and second regions are
different for different positions of the fiducial. The first and
second signals, are therefore functions of the position of the
fiducial and thereby of the position of the latch needle on which
the fiducial is located. The controller uses the first and second
signals to determine the position of the latch needle.
[0038] In another preferred embodiment of the present invention the
fiducial imager comprises a lens, a detector and a light filter.
The detector comprises a light sensitive surface sensitive to light
in first and second non-overlapping wavelength bands of light. The
light filter has first and second filter regions. Each of the
filter regions transmits light in a different one of the wavelength
bands and does not transmit light in the other wavelength band. The
areas of the two filter regions are preferably equal and preferably
abut each other along a straight dividing line.
[0039] The lens focuses light from the fiducial illuminator that is
reflected from the fiducial to form an image of the fiducial on the
light sensitive surface of the detector. The filter is positioned
with respect to the detector and lens so that the dividing line of
the filter and the optic axis of the lens intersect and so that all
light from the fiducial focused on the light sensitive surface of
the detector passes through the filter. (The filter can also be
comprised in an appropriate coating on the lens.) As a result
reflected light from the fiducial incident on a first one half of
the lens is filtered by the first filter region and reflected light
from the fiducial incident on the other half of the lens, a "second
half", is filtered by the second filter region. Therefore the
amounts of light in the image of the fiducial in the first and
second wavelength bands are proportional to the amounts of light
incident on the first and second halves of the lens
respectively.
[0040] Preferably, the fiducial illuminator illuminates the
fiducial with substantially equal intensities of light in the first
and second wavelength bands and the fiducial has substantially the
same reflectivity for light in both wavelength bands. Preferably,
the transmittance of the first filter region for light in the first
wavelength band is substantially equal to the transmittance of the
second filter region for light in the second wavelength band.
Preferably, intensities registered by the light sensitive surface
in the first and second wavelength bands are normalized to the
intensities of light radiated by the fiducial illuminator in the
first and second wavelength bands. The intensities are preferably
corrected for differences in reflectivity of the fiducial in the
two wavelength bands. Preferably, the intensities are corrected for
differences between the transmittance of the first filter region
for light in the first wavelength band and the transmittance of the
second filter region for light in the second wavelength band. The
intensities are preferably corrected for differences in sensitivity
of the light sensitive surface to light in the two wavelength
bands.
[0041] Hereinafter, when intensities, integrated intensities or
amounts of light on light sensitive surfaces are compared, it is
understood that they are appropriately normalized to the intensity
of light radiated by the fiducial illuminator and corrected for
biases introduced by various optical components.
[0042] The amounts of light incident on the first and second halves
of the lens are functions of the position of the fiducial. When the
fiducial is located on the optic axis of the lens the first and
second halves of the lens receive the same amounts of reflected
light. When the fiducial is displaced from the optic axis in the
direction of one or the other halves of the lens, the half towards
which the fiducial is displaced gets more light and the other half
gets less light. Preferably, the dividing line of the filter is
substantially perpendicular to the motion of the latch needle and
thereby to the fiducial in order to maximize change in the amounts
of light incident on the first and second halves of the lens with
change of position of the fiducial. The first and second signals
sent by the detector to the controller are therefore functions of
the position of the fiducial. These signals are used by the
controller to determine the position of the fiducial and the latch
needle on which the fiducial is located.
[0043] In an alternate preferred embodiment of the present
invention, the fiducial imager comprises two preferably identical
light detectors, each having its own lens that focuses an image of
the fiducial onto the detector's light sensitive surface. The two
light detectors are displaced from each other by a short distance.
The line between the two detectors is aligned parallel with and in
the plane of the latch needle slot of the latch needle whose
position the detectors are used to determine. The difference
between the amounts of light from the fiducial illuminator that is
reflected into each of the two detectors is different for different
positions of the latch needle along the latch needles range of
motion. For example, assume the fiducial illuminator is equidistant
from both detectors. When the fiducial is equidistant from both
detectors each detector receives the same amount of reflected light
from the fiducial and the difference between the amounts of light
received by the detectors is substantially zero. If the fiducial is
displaced along the direction of motion of the latch needle towards
one of the detectors, the detector towards which it is displaced
receives an increased amount of reflected light and the other
detector receives a decreased amount of light. The difference
between the amounts of reflected light received by the detectors
from the fiducial is a function of the displacement of the fiducial
from the position of the fiducial at which both detectors receive
the same amount of reflected light. This difference, and thereby
the location of the fiducial and the latch needle, is determined by
a circuit that receives an input signal from each detector that is
a function of the intensity of light incident on the detector.
[0044] In another preferred embodiment of the present invention the
fiducial imager comprises one light detector and two lenses. The
light sensitive surface of the light detector is sensitive to light
in two non-overlapping wavelength bands of light. The fiducial
illuminator illuminates the fiducial with preferably equal
intensities of light from both wavelength bands. Each of the lenses
transmits light in only one of the two different wavelength bands.
Both lenses focus light reflected from the fiducial onto the light
sensitive surface of the detector. The lenses are displaced a short
distance from each other and the line connecting the centers of the
lenses is aligned parallel with and in the plane of the latch
needle slot of the latch needle whose position the fiducial imager
is used to determine. As in the previous fiducial imager, when the
fiducial is equidistant from both lenses the detector registers
equal intensity (appropriately normalized as discussed above) of
light in both of the wavelength bands for which it is sensitive. As
the fiducial is displaced towards one or the other of the lenses,
the difference between the intensities of light registered by the
detector in the two wavelength bands changes as a function of the
amount of the displacement.
[0045] In a yet another preferred embodiment of the present
invention, the fiducial imager comprises one light detector and a
lens. The light sensitive surface of the light detector is
sensitive to light in two non-overlapping wavelength bands of
light. The lens transmits light in both of the two wavelength
bands. The latch needle whose position is measured using the
fiducial imager is provided with two fiducials displaced from each
other by a short distance along the length of the latch needle.
Each of the fiducials reflects light in a different one of the
wavelength bands to which the detector is sensitive and absorbs
light in the other wavelength band. The lens focuses both fiducials
on the light sensitive surface of the light detector. The
difference between the light intensity registered by the detector
in the two different wavelength bands is used to determine the
position of the two fiducials and thereby of the latch needle.
[0046] In still yet another preferred embodiment of the present
invention, the fiducial imager comprises a monochromatic light
detector having a pixelated light sensitive surface, such as a CCD,
and a lens that focuses an image of the fiducial on the pixelated
surface. The location of the fiducial image on the pixelated
surface is determined to be the center of gravity of the
illumination pattern on the surface that is caused by the fiducial
image. The location of the center of gravity is determined to
sub-pixel resolution from the locations of pixels illuminated by
the fiducial image and the intensities with which these pixels are
illuminated using techniques known in the art. The position of the
fiducial and its latch needle is determined from the location of
the fiducial image on the pixelated surface by techniques that are
well-known in the art.
[0047] It should be realized that an OPM, in accordance with a
preferred embodiment of the present invention, is useable for any
application requiring position monitoring of latch needles and its
use is not restricted for use only in cooperation with a DND
system. It should also be realized that an OPM, in accordance with
a preferred embodiment of the present invention, is useable for
providing latch needle position measurements for a DND system
irrespective of the type of actuators used to activate latch
needles in the DND system, and is not limited to use with DND
systems that use piezoelectric micromotors or actuators.
[0048] There is therefore provided in accordance with a preferred
embodiment of the present invention an optical position monitor for
determining the position of a latch needle in a knitting machine
comprising: at least one fiducial at a known fixed location on the
body of the latch needle; a fiducial imager that produces at least
one optical image of the at least one fiducial on at least one
light sensitive surface, wherein the at least one optical image
changes with changes in position of the at least one fiducial; and
a controller that receives at least one signal responsive to the
changes in the at least one image and uses the at least one signal
to determine the position of the at least one fiducial and thereby
of the latch needle.
[0049] Preferably, the optical position monitor comprises at least
one fiducial illuminator that illuminates the at least one
fiducial. Additionally or alternatively, the changes in the at
least one image comprise changes in integrated intensity of the at
least one image. Alternatively or additionally, the at least one
fiducial comprises a single fiducial.
[0050] In some preferred embodiments of the present invention the
at least one light sensitive surface comprises first and second
light sensitive surfaces and the at least one signal comprises
first and second signals responsive to the intensity of light
reflected by the at least one fiducial imaged on the first and
second light sensitive surfaces respectively.
[0051] Preferably, the first and second light sensitive surfaces
comprise first and second contiguous light sensitive surfaces. The
at least one image preferably comprises a single image having first
and second portions on the first and second light sensitive
surfaces respectively and the ratio between the first and second
portions depends upon the position of the at least one
fiducial.
[0052] Alternatively, the first and second light sensitive surfaces
comprise first and second light sensitive surfaces that are
preferably displaced from each other by a distance. Preferably, the
optical position monitor comprises first and second lenses and the
at least one image comprises first and second images, wherein the
first and second light sensitive surfaces are optically aligned
with the first and second lenses respectively, and the first lens
produces the first image on the first light sensitive surface and
the second lens produces the second image on the second light
sensitive surface and wherein the ratio between the integrated
intensities of the first and second images depends upon the
position of the at least one fiducial.
[0053] In still other preferred embodiments of the present
invention the at least one light sensitive surface comprises a
single light sensitive surface sensitive to light in first and
second non-overlapping wavelength bands of light and the at least
one signal comprises first and second signals responsive to the
integrated intensity of light incident on the single light
sensitive surface in the first and second wavelength bands
respectively.
[0054] Preferably, the optical position monitor comprises a light
filter having first and second filter regions wherein the first
region transmits light only in the first wavelength band and the
second filter region transmits light only in the second wavelength
band and light reflected from the single fiducial that is imaged on
the light sensitive surface, passes through either the first filter
region or the second filter region.
[0055] Preferably, the at least one image comprises a single image,
wherein a first portion of light in the single image reflected from
the fiducial passes through the first filter region and a second
portion of light in the single image reflected from the fiducial
passes through the second filter region, and wherein the ratio
between first and second portions depends upon the position of the
fiducial.
[0056] Alternatively, the optical position monitor comprises a
first lens and a second lens displaced from each other by a
distance, wherein the first lens transmits light only in the first
wavelength band and the second lens transmits light only in the
second wavelength band, wherein the first and second lenses produce
first and second images of the fiducial on the light sensitive
surface respectively, and the relative integrated intensity of
light in the first and second images is a function of the position
of the fiducial.
[0057] In some preferred embodiments of the present invention the
at least one fiducial comprises at least a first and a second
fiducial. Preferably, the at least one light sensitive surface
comprises a single light sensitive surface sensitive to light in
first and second non-overlapping wavelength bands of light and
wherein the at least one signal comprises first and second signals
responsive to the integrated intensity of light incident on the
single light sensitive surface in the first and second wavelength
bands respectively. Preferably, the first fiducial reflects light
only in the first wavelength band and the second fiducial reflects
light only in the second wavelength band, and the optical position
monitor comprises: a lens that produces a first image of the first
fiducial and a second image of the second fiducial on the light
sensitive surface using light reflected from the first and second
fiducials respectively; wherein the integrated intensity of light
in the first and second images depends upon the position of the
first and second fiducials.
[0058] In an optical position monitor in accordance with some
preferred embodiments of the present invention, changes in the at
least one image comprise changes in the location of the at least
one image on the at least one light sensitive surface. Preferably,
the at least one light sensitive surface comprises at least one
pixelated surface. Preferably, the at least one signal comprises
signals responsive to the intensity of light incident on each pixel
of the at least one pixelated surface. The at least one image
preferably comprises a single image on each of the at least one
pixelated surface. In some preferred embodiments of the present
invention the at least one pixelated surface comprises a single
pixelated surface.
[0059] In some preferred embodiments of the present invention a
location for each of the at least one image is defined as the
location of an optical center of gravity of the at least one image,
which location is determined from the signals responsive to the
intensity of light incident on each pixel of the at least one
pixelated surface, and wherein the location of the optical center
of gravity is responsive to the position of the at least one
fiducial.
[0060] In some preferred embodiments of the present invention
wherein changes in the at least one image comprise changes in the
location of the at least one image on the at least one light
sensitive surface, the at least one fiducial comprises a single
fiducial.
[0061] In some preferred embodiments of the present invention the
single fiducial of a plurality of latch needles is imaged on
different regions of the at least one pixelated surface, and the
optical position monitor is used to determine the positions of a
plurality of latch needles. Preferably, the number of the plurality
of latch needles is greater than 5. Alternatively, the number of
the plurality of latch needles is preferably greater than 10.
Alternatively, the number of the plurality of latch needles is
preferably greater than 20.
[0062] In some preferred embodiments of the present invention an
optical position monitor comprises a means for selectively aligning
the optical position monitor with different latch needles in the
needle bed.
[0063] There is further provided an optical position monitor for
simultaneously monitoring the position of a plurality of latch
needles in a knitting machine needle bed, which needle bed has a
plane surface having latch needle slots that are parallel to each
other, comprising a plurality of optical position monitors in
accordance with a preferred embodiment of the present
invention.
[0064] Preferably, each of the plurality of the optical position
monitors is aligned with a different latch needle and is used to
determine the position of at least the latch needle with which it
is aligned.
[0065] The optical position monitors in the plurality of optical
position monitors are preferably aligned in a line array along a
straight line. Preferably, the line array is parallel to the needle
bed surface and perpendicular to the latch needle slots.
Alternatively or additionally, the spacing between an optical
position monitor in the line array and an adjacent optical position
monitor is the same for any optical position monitor in the line
array. Preferably, the spacing is equal to the spacing between
adjacent latch needles of the plurality of latch needles.
[0066] In some preferred embodiments of the present invention, the
number of the plurality of needles is equal to the number of
needles in the needle bed.
[0067] In other preferred embodiments of the present invention the
number of the plurality of latch needles is less than the number of
needles in the needle bed and the optical position monitor includes
a means for selectively aligning the optical position monitor with
different groups of latch needles in the needle bed. Preferably the
means for aligning the optical position monitor with different
groups of latch needles comprises means for translating the optical
position monitor in a direction parallel to the needle bed and
perpendicular to the latch needle slots.
[0068] In some preferred embodiments of the present invention the
optically reflective fiducial comprises at least two regions on the
surface of the latch needle having different reflectivities.
Preferably, at least one of the at least two regions comprises a
retroreflector. Alternatively or additionally, at least one of the
at least two regions comprises at least one discontinuity in the
surface of the latch needle. Preferably, the at least one
discontinuity comprises at least one straight line groove on the
surface of the latch needle. Alternatively or additionally, the
discontinuity preferably comprises at least one dimple depressed
into the surface of the latch needle. Alternatively or
additionally, at least one of the at least two regions is
preferably substantially non-reflecting.
[0069] Additionally or alternatively, light reflected from the
fiducial is substantially confined within a cone of half energy
angle less than 20.degree.. Additionally or alternatively light
reflected from the fiducial is substantially confined within a cone
of half energy angle less than 15.degree.. Additionally or
alternatively, light reflected from the fiducial is substantially
confined within a cone of half energy angle less than
10.degree..
[0070] There is further provided an actuator system for activating
a latch needle, which latch needle has a shaft, comprising: a flat
planar extension of the shaft having first and second parallel
planar surfaces; at least one piezoelectric micromotor having a
first surface region for transmitting motion to a moveable element,
which first surface region is resiliently pressed to the first
surface and at least one additional piezoelectric motor having a
second surface region for transmitting motion to a moveable element
which second surface region is resiliently pressed to the second
surface; and wherein vibratory motions of the first and second
surface regions apply forces to the flat extension that cause
motion in the latch needle.
[0071] There is also provided an actuator system for activating a
latch needle, which latch needle has a thin flat shaft comprising:
a flat planar extension of the shaft having first and second planar
surfaces; a piezoelectric micromotor having a surface region for
transmitting motion to a moveable element; a transmission bracket
for holding the piezoelectric micromotor, the transmission bracket
comprising a bearing surface and a means for resiliently urging the
surface region of the piezoelectric micromotor towards the bearing
surface; and wherein the flat extension is inserted between the
surface region of the piezoelectric micromotor and the bearing or
the non-stick surface and wherein vibratory motion of the surface
region applies force to the flat extension causing motion in the
latch needle.
[0072] Preferably, the bearing surface is the surface of a
rotatable roller or ball. Alternatively or additionally, the
bearing surface is a surface having a low friction coating.
[0073] In an actuator system for activating a latch needle
according to some preferred embodiments of the present invention,
the surface region for transmitting motion to a moveable element
comprises a wear resistant nub that makes contact with a surface of
the moveable element towards which the surface region for
transmitting motion is resiliently pressed in order to transmit
motion to the moveable element.
[0074] In an actuator system for activating a latch needle
according to some preferred embodiments of the present invention,
points on surfaces of the flat extension at which said surface
regions of the piezoelectric micromotors make contact are clad in
wear resistant material.
BRIEF DESCRIPTION OF FIGURES
[0075] The invention will be more clearly understood by reference
to the following description of preferred embodiments thereof read
in conjunction with the attached figures listed below, wherein
identical structures, elements or parts that appear in more than
one of the figures are labeled with the same numeral in all the
figures in which they appear, and in which:
[0076] FIG. 1 shows the basic structure of a latch needle;
[0077] FIG. 2 is a schematic illustration of a conventional system
for activating latch needles in a knitting machine;
[0078] FIG. 3 is a schematic illustration of a system for coupling
piezoelectric micromotors to latch needles in a needle bed by
rotary transmission, in accordance with a preferred embodiment of
the present invention;
[0079] FIG. 4 shows a schematic of a system for coupling
piezoelectric micromotors to latch needles in a needle bed by
linear transmission in accordance with an alternative preferred
embodiment of the present invention;
[0080] FIG. 5 illustrates schematically the coupling of a latch
needle with a coupling fin to two piezoelectric micromotors in
accordance with a preferred embodiment of the present
invention;
[0081] FIG. 6 illustrates schematically the coupling of a latch
needle with a coupling fin to a single piezoelectric micromotor
mounted to a transmission bracket in accordance with yet another
preferred embodiment of the present invention;
[0082] FIGS. 7A-7C schematically illustrate an OPM comprising a
single fiducial imager, imaging a latch needle fiducial, in
accordance with a preferred embodiment of the present
invention;
[0083] FIG. 8 schematically illustrates an OPM comprising a linear
array of a plurality of imaging fiducials shown in FIGS. 7A-7C,
imaging an equal plurality of latch needle fiducials in accordance
with a preferred embodiment of the present invention;
[0084] FIGS. 9A-9C schematically illustrate an OPM comprising a
single fiducial imager, imaging a latch needle fiducial, in
accordance with an alternative preferred embodiment of the present
invention;
[0085] FIGS. 10A-10C schematically illustrate an OPM comprising a
single fiducial imager, imaging a latch needle fiducial, in
accordance with another preferred embodiment of the present
invention;
[0086] FIGS. 11A-11C schematically illustrate an OPM comprising a
single fiducial imager, imaging a latch needle fiducial, in
accordance with yet another preferred embodiment of the present
invention;
[0087] FIGS. 12A-12C schematically illustrate an OPM comprising a
single fiducial imager, imaging a latch needle fiducial, in
accordance with still another preferred embodiment of the present
invention; and
[0088] FIGS. 13A-13C schematically illustrate an OPM comprising a
single fiducial imager, imaging a latch needle fiducial, in
accordance with another alternative preferred embodiment of the
present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0089] FIG. 1 shows a profile of a latch needle 20. Latch needle 20
is a thin metallic structure with a long shaft 22 having a hook 24
and a tip 30 formed on one of its ends. A latch 26 is rotatable
about a pivot 28 and is shown in the figure in the position where
it caps tip 30 to close hook 24 and prevents hook 24 from hooking a
thread. In an open position latch 26 is rotated clockwise almost to
a position where it is parallel to shaft 22. A fin 32 extends out
from shaft 22, generally on the same side of shaft 22 as hook
24.
[0090] FIG. 2 is a schematic illustration of the arrangement of
needle beds in a conventional knitting machine and a shuttle which
transmits motion to latch needles in the needle beds.
[0091] Two needle beds 36 and 38 are rigidly joined at an angle to
each other so that an edge 39 of needle bed 36 is close to and
parallel to an edge 40 of needle bed 38. A long narrow space 44
separates edge 39 and edge 40. Needle beds 36 and 38 are identical
or very similar and detailed discussion will be confined to needle
bed 36 with the understanding that details and structures described
for needle bed 36 apply equally to needle bed 38.
[0092] Threads to be woven into fabric (not shown) are held under
tension close to and parallel to edges 39 and 40. Fabric (not
shown), as it is produced moves downwardly from edges 39 and 40
into space 44. As the fabric moves down it exits the knitting
machine.
[0093] Needle bed 36 is provided with an array of equally spaced
parallel latch needle slots 42 that are perpendicular to edge 39. A
latch needle 20 is placed in each latch needle slot 42. The bodies
of latch needles 20 are completely inside latch needle slots 42 and
are not visible. Only fins 32 of latch needles 20 protrude above
the surface of needle bed 36 and are visible. Fins 32 of all latch
needles 20 that are at rest in slots 42 are aligned along a
straight row which is perpendicular to latch needle slots 42. Each
needle 20 is moveable back and forth in its latch needle slot
42.
[0094] A shuttle 46, having ends 52 and 54, moves back and forth
parallel to edges 39 and 40 along the length of needle bed 36. An
interior face 48 of shuttle 46 is parallel to needle bed 36 and has
a channel 50 formed in the face. Channel 50 is open on both ends 52
and 54 of shuttle 46. The two open ends of channel 50 are in line
with the row of fins 32. A section 56 of channel 50 is not
collinear with the ends of channel 50. Channel 50 is just wide
enough and deep enough so that fins 32 can pass into and move
through it.
[0095] As shuttle 46 moves back and forth with interior face 48
parallel to latch needle bed 36, fins 32 of latch needles 20 enter
channel 50 at one end and move along the length of channel 50. When
a fin 32 of a latch needle 20 encounters non-collinear section 56
of channel 50 the fin 32 and the latch needle 20 to which fin 32 is
attached are displaced parallel to latch needle slot 42 in which
the latch needle 20 is found. In FIG. 2, for clarity of
presentation, only a few of latch needles 20 that are moving in
channel 50 are shown.
[0096] FIG. 3 shows a system for exclusively coupling each of the
latch needles in a needle bed to at least one exclusive
piezoelectric micromotor using a rotary transmission, according to
a preferred embodiment of the present invention. A long bearing
shaft 58 is mounted over a needle bed 60 that is provided with
slots 62 into which have been placed latch needles 63. Bearing
shaft 58 is mounted with a multiplicity of thin annuli 64, one
annulus for each latch needle (for clarity only three are shown).
The annuli rotate freely on bearing shaft 58. Each annulus is
positioned opposite a fin 65 of a particular latch needle 63. A
connecting arm 66 connects each annulus 64 to a point 68 on fin 65,
to which annulus 64 is opposite. The connection at point 68 is a
flexible or slideable connection produced by methods known in the
art. One or more piezoelectric micromotors 70, 72, and 74, are
resiliently pressed against each annulus 64 by methods known in the
art. When piezoelectric micromotors 70, 72, and 74, are activated
they cause annulus 64 and connecting arm 66 to rotate, which in
turn moves latch needle 63 linearly in its slot 62. The flexible
connection at point 68 translates rotational motion of arm 66 to
linear motion of latch needle 63. It should be understood that this
arrangement allows for a much higher speed of the latch needle than
that available from the motor itself.
[0097] While three exclusive piezoelectric micromotors are shown
coupled to annulus 64 in FIG. 3, a greater or lesser number of
micromotors can be used depending on the speed or torque required
for motion of the needle. Also, other types of piezoelectric
micromotors constructed differently than the ones shown in FIG. 3
and described above may be used to rotate annulus 64 and are
advantageous. U.S. Pat. No. 4,562,374 and the publication by
Hiroshi et al., IEEE Transactions on Ultrasonics, Ferroelectrics,
and Frequency Control, Vol. 42, No. 2, March 1995, incorporated
herein by reference, describe rotary piezoelectric micromotors.
These rotary piezoelectric micromotors comprise a cylindrical,
annular or disc shaped rotor that is caused to rotate by coupling
to a stator that is a cylindrical, annular or disc shaped vibrator.
The rotor and stator are concentric. A vibrating surface of the
stator is coupled to an inside edge surface or an outside edge
surface of the rotor to impart a rotary motion to it.
Alternatively, a vibrating surface of the stator may be coupled to
a face surface of the rotor to impart rotational motion to the
rotor. Annulus 64 can be rotated by the use of stators similar to
those described in the above references. Annulus 64 is coupled to
the stators in similar fashion to the way that the rotors are
coupled to the stators in the described rotary piezoelectric
micromotors.
[0098] FIG. 4 shows another system for coupling each of the latch
needles in a needle bed to at least one exclusive piezoelectric
micromotor using a linear transmission, according to an alternative
preferred embodiment of the present invention.
[0099] A latch needle bed 76 is provided with latch needle slots 78
in which are placed latch needles 80. One or more thin
piezoelectric micromotor 82 is resiliently pressed against the
shaft 84 of each latch needle 80 (only one is shown for each latch
needle for simplicity). Piezoelectric micromotors 82 on adjacent
latch needles 80 are in line with each other so that they form a
straight row. Alternatively, piezoelectric micromotors 82 may be
staggered with respect to each other so that they are arrayed in
two or more parallel rows. FIG. 4 shows an embodiment according to
the present invention in which piezoelectric micromotors are
aligned in two parallel rows. Staggered configurations allow for
more space between closely packed vibrators 82 than would be
available if vibrators 82 were arrayed in a single row and thus
allow for thicker more powerful piezoelectric micromotors to be
coupled to latch needles 63.
[0100] Vibrations of piezoelectric micromotors 82 are directly
translated into linear motion of latch needles 80. Slots 78 are
fitted with bearings (not shown) or with a non-stick surface so
that the resilient force which presses a vibrator 82 to a shaft 84
of a needle 80 does not result in excessive friction between needle
80 and the bottom or sides of latch needle slot 78 in which needle
80 is placed.
[0101] Rotary piezoelectric micromotors similar to those described
in U.S. Pat. No. 4,562,374 and the publication by Hiroshi et al.
cited above may also be used to drive latch needles 80. The edge
surface of a rotor of a rotary piezoelectric micromotor is
resiliently pressed against shaft 84 of each latch needle 80. The
axes of the rotors are perpendicular to latch needle slots 78 in
which latch needles 80 are placed. Frictional forces at the area of
contact between the edge surface of a rotor and the surface of
shaft 84 of a needle 80 acts to prevent the edge surface of the
rotor from slipping on the surface of shaft 84 when the rotor
rotates. As the rotor rotates it therefore causes shaft 84 of latch
needle 80 to displace linearly in latch needle slot 78 in which
latch needle 80 is placed in the direction of motion of the mass
points of the edge surface of the rotor which are in contact with
the surface of shaft 84.
[0102] FIG. 5 shows a latch needle 300 coupled to two identical
piezoelectric micromotors 302 and 304, in accordance with yet
another preferred embodiment of the present invention. Latch needle
300 comprises a latch needle shaft 301 and a coupling fin 306.
Coupling fin 306 has two parallel planar surfaces 308 and 310. A
coupling region 312 of each surface 308 and 310 (coupling region
312 of surface 308 is not seen in the perspective of FIG. 5) is
preferably clad with a wear resistant material suitable for
friction coupling with piezoelectric micromotors.
[0103] Piezoelectric micromotors 302 and 304 preferably comprise
friction nubs 314 and 316 respectively. Piezoelectric micromotors
302 and 304 are resiliently pressed to coupling fin 306 so that
friction nubs 314 and 316 contact coupling regions 312 of surfaces
308 and 310 respectively at points that are directly opposite each
other. In order to move latch needle 300 back and forth in its
latch needle slot (not shown) piezoelectric micromotors 302 and 304
are preferably simultaneously activated in phase to transmit motion
to coupling fin 306.
[0104] FIG. 6 shows latch needle 300 coupled to a single
piezoelectric micromotor 320, in accordance with still another
preferred embodiment of the present invention. Piezoelectric
micromotor 320 is mounted to a transmission bracket 322 preferably
comprising a bearing 324 and a biasing means 326 such as a spring
or resilient pad. Dashed lines indicate parts of piezoelectric
micromotor 320 hidden by transmission bracket 322. Piezoelectric
micromotor 320 preferably comprises a friction nub 328 (shown in
dashed lines). Biasing means 326 resiliently presses piezoelectric
micromotor 320 in a direction so that friction nub 328 is urged
towards bearing 324. Transmission bracket 322 is held by an
appropriate mechanical structure (not shown) so that coupling fin
306 is located between friction nub 328 and bearing 324.
[0105] As a result of the action of biasing means 326 bearing 324
presses resiliently on coupling region 312 of surface 310 and
friction nub 328 presses resiliently on coupling region 312 of
surface 308. Transmission bracket 322 is oriented so that the
direction in which friction nub 328 is urged by biasing means 326
is substantially perpendicular to the plane of coupling fin 306.
Bearing 324 and friction nub 328 exert equal and opposite forces on
coupling fin 306 perpendicular to the plane of coupling fin 306. As
a result piezoelectric micromotor 320 does not produce a torque on
latch needle 300 that tends to rotate latch needle 300 in its latch
needle slot (not shown).
[0106] Coupling fin 306 can be located at different positions along
shaft 301 of different latch needles 300. In addition coupling fin
306 can be formed so that it extends different distances from shaft
301 of different latch needles 300. Adjacent latch needles in a
needle bed can therefore preferably, have coupling fins that
protrude different heights above the needle bed and/or are
displaced with respect to each other in a direction parallel to
their shafts in order to provide space for piezoelectric
micromotors that are coupled to the coupling fins.
[0107] It is clear from the above discussion that piezoelectric
micromotors in accordance with preferred embodiments of the present
invention can be conveniently coupled to latch needles in a latch
needle bed of a knitting machine so that each latch needle is
exclusively coupled to at least one piezoelectric micromotor.
[0108] FIGS. 7A-7C schematically illustrate an OPM 98 comprising a
fiducial imager 100 and a fiducial illuminator 101 imaging a latch
needle fiducial 102 located on a latch needle 104, in accordance
with a preferred embodiment of the present invention. Fiducial
imager 100 comprises a lens 106 and a detector 108. Detector 108
has a light sensitive surface 110 (shown greatly exaggerated in
thickness for convenience and clarity of presentation) that is
divided into a first detector region 112 and a second detector
region 114. A region of Light sensitive region 110 is schematically
shown from "underneath", in a ventral view, as seen from fiducial
102, in views 116, 118 and 120 to the left of detector 108 in each
of FIGS. 7A-7C respectively. The areas of detector regions 112 and
114 preferably have the same shape, are equal and abut each other
along a straight dividing line 122. Detector 108 registers the
intensity of light incident on first detector region 112 and second
detector region 114 separately. Detector 108 sends a first signal
to a controller (not shown) that is a function of the intensity of
light registered on first detector region 112 and a second signal
to the controller that is a function of the intensity of light
registered by second detector region 114.
[0109] Detector 108 is oriented with respect to latch needle 104 so
that dividing line 122 is substantially perpendicular to the plane
(the same as the plane of FIGS. 7A-7C) of the latch needle slot
(not shown,) in which latch needle 104 is held, and perpendicular
to the direction of the back and forth motion of latch needle 104
indicated by doubled headed arrow 124.
[0110] Fiducial 102 is illuminated by light from fiducial
illuminator 101 and reflects some of the light, indicated by dotted
line 128, onto lens 106. Fiducial 102 preferably reflects light
from fiducial illuminator 101 diffusely in a cone (not shown) of
half energy angle on the order of 10.degree.-15.degree.. Fiducial
illuminator 101 and fiducial imager 100 are located with respect to
each other so that for any position of latch needle 104 in the
operating range of motion of latch needle 104, fiducial 102
reflects light from fiducial illuminator 101 into fiducial imager
100.
[0111] Lens 106 forms an image 130 of fiducial 102 on light
sensitive surface 110 from the light reflected by fiducial 102. A
first image portion 132 of image 130 falls on first detector region
112 and a second image portion 134 of image 130 falls on second
detector region 114 (views 116, 118 and 120). First detector region
112 registers an intensity of light on its surface that is a
function of the size of first image portion 130 and second detector
region 114 registers an intensity of light that is a function of
the size of second image portion 134. Detector 108 therefore sends
a first signal to the controller that is as function of the size of
first image portion 130 and a second signal to the controller that
is a function of the size of second image portion 134. The relative
sizes of first image portion 132 and second image portion 134 are a
function of the position of fiducial 102 and first and second
signals are used by the controller to determine the position of
fiducial 102 and thereby of latch needle 104.
[0112] The dependence of the sizes of first image portion 132 and
second image portion 134 on the position of fiducial 102 is shown
schematically in ventral views (seen from "beneath", from the
perspective of fiducial 102) 116, 118 and 120 in FIGS. 7A-7C
respectively. In FIG. 7A fiducial 102 is located along the axis of
fiducial imager 100, which is coincident with the direction of line
128 that indicates the direction of reflected light from fiducial
102. First image portion 132 and second image portion 134 are
equal. In FIG. 7B fiducial 102 is shown displaced far to the right
of the axis of fiducial imager 100 and first image portion 132 is
much larger than second image portion 134. In FIG. 7C fiducial 102
is shown displaced far to the left of the axis of fiducial imager
102 and second image portion 134 is much larger than first image
portion 132.
[0113] FIG. 8 shows an OPM 138, in accordance with a preferred
embodiment of the present invention, that comprises a plurality of
fiducial imagers 100 shown in FIGS. 7A-7C. Fiducial imagers 100 are
fixed with respect to each other by an appropriate mechanical
structure (not shown) in a collinear line array 140 having an axis
142. Line array 140 is mounted over a needle bed (not shown) of a
knitting machine (not shown) in which a plurality of latch needles
104 are placed. Each latch needle 104 has a fiducial 102. Axis 142
of line array 140 is preferably parallel to the surface of the
needle bed and perpendicular to latch needles 104 (and thereby
perpendicular to the directions of motion of latch needles 104).
Dividing lines 122 (not shown) of light sensitive surfaces 110 of
fiducial imagers 100 are preferably parallel to axis 142. Each of
fiducial imagers 100 in line array 140 is aligned over a different
one of latch needles 104 and is used to measure the position of
latch needle 104 over which it is aligned.
[0114] In OPM 138, each fiducial 102 is illuminated with light from
a fiducial illuminator 101 and reflects some of this light into the
fiducial imager 100 that is aligned over and images the fiducial
102. A central ray of light from each fiducial 102 reflected into
the fiducial imager 100 that images the fiducial 102 is indicated
by a dotted line 128. Each dotted line 128 starts at a fiducial
102, and ends on the image 130 of the fiducial 102 in the fiducial
imager 100 that is used to measure the position of fiducial 102.
The positions of the first and second leftmost latch needles 104
and their fiducials 102 in FIG. 8 correspond to the positions of
latch needles 104 and fiducials 102 shown in FIGS. 7C and 7A
respectively. The positions of the rest of latch needles 104 shown
in FIG. 8 correspond to the position of latch needle 104 shown in
FIG. 7B.
[0115] OPM 138 can be used to determine positions only for those
latch needles 104 that are aligned with a fiducial imager 100 of
line array 140. At any one time therefore, the number of latch
needles 104 in a knitting machine whose positions can be determined
by OPM 138 is equal to the number of fiducial imagers in line array
140. Preferably, the number of fiducial imagers 100 in line array
140 is equal to the number of latch needles in the knitting
machine. If the number of the fiducial imagers in line array 140 is
less than the number of latch needles in the knitting machine, OPM
138 must be moved in order to provide position measurements for all
latch needles 104 in the knitting machine. Preferably, OPM 138 is
moved parallel to axis 142 along the knitting machine needle bed in
order to provide position measurements for all the latch needles
104 in the knitting machine.
[0116] In FIG. 8 each fiducial 102 is shown illuminated by its own
fiducial illuminator 101. This is not a necessity and some OPMs, in
accordance with preferred embodiments of the present invention,
comprise fiducial illuminators that illuminate groups of more than
one fiducial 102. Additionally, in some preferred embodiments of
the present invention, lenses 106, each of which is used to image
one fiducial 102, are replaced by lenses, such as extended
cylindrical lenses, each of which is used to image more than one
fiducial 102.
[0117] FIGS. 9A-9C schematically illustrate an OPM 270 imaging
fiducial 102 of latch needle 104, in accordance with an alternate
preferred embodiment of the present invention. OPM 270 comprises a
fiducial imager 272 and a fiducial illuminator 274. Fiducial imager
272 comprises a lens 276 having an optic axis indicated by line
278, a detector 280 and a light filter 282. Detector 280 comprises
a light sensitive surface 282, sensitive to light in first and
second non-overlapping wavelength bands of light. Detector 280
sends a first signal to a controller (not shown) that is a function
of the intensity of light registered on light sensitive surface 280
in the first wavelength band and a second signal to the controller
that is a function of the intensity registered by light sensitive
surface 282 in the second wavelength band.
[0118] Light filter 282 has a first filter region 284 and a second
filter region 286. First filter region 284 transmits light only in
the first wavelength band and second filter region 286 transmits
light only in the second wavelength band. First and second filter
regions 284 and 286 are preferably equal and abut each other along
a straight dividing line (not shown in fiducial imager 272). Filter
282 is oriented with respect to lens 276 so that reflected light
from fiducial 102 incident on lens 276 passes through filter 282. A
central ray of reflected light from fiducial 102 is indicated by
dotted line 288 in FIGS. 9B and 9C. In FIG. 9A the central ray is
coincident with optic axis 278. The dividing line of filter 282 and
optic axis 278 of lens 276 intersect. Preferably, the dividing line
is perpendicular to the direction of motion of latch needle 104 and
the plane (the plane of the Fig.) of the latch needle slot (not
shown) that holds latch needle 104. As a result, light incident on
a first half 290 of lens 276 is filtered by first filter region 284
and light incident on a second half 292 of lens 276 is filtered by
second filter region 286. Lens 276 focuses reflected light from
fiducial 102 to form an image 130 of fiducial 102 on light
sensitive surface 282 of detector 280. A first portion of the
intensity of image 130 results from light incident on first half
290 of lens 276 and a second portion of the intensity of image 130
results from light incident on second half 292 of lens 276. Since
first half 290 of lens 276 is filtered by first filter region 284,
the first portion of the intensity of image 130 results from light
in the first wavelength band. Similarly, the second portion of the
intensity of image 130 results from light in the second wavelength
band. The first and second portions of the intensity of image 130
are proportional to the amounts of light from fiducial 102 that are
incident on first and second halves 290 and 292 of lens 276
respectively. As a result, the intensities of light registered by
light sensitive surface 282 in the first and second wavelength
bands are proportional to the amounts of reflected light from
fiducial 102 incident on first and second halves 290 and 292 of
lens 276 respectively.
[0119] However, the amounts of light incident on first half 290 and
second half 292 are functions of the location of fiducial 102 with
respect to optic axis 278 of lens 276. When fiducial 102 is on
optic axis 278, halves 290 and 292 of lens 276 receive the same
amounts of reflected light. When fiducial 102 is displaced along
the direction of motion of latch needle 104 (along the direction of
double headed arrow 124 in FIGS. 9A-9C) towards one or the other of
halves 290 and 292, the half towards which fiducial 102 is
displaced receives more light and the other half less light. This
is because the distance from fiducial 102 to the half of lens 276
towards which fiducial 102 is displaced decreases and the distance
towards the other half increases. The first and second signals that
detector 280 sends to the controller are therefore functions of the
position of fiducial 102. These signals are used by the controller
to determine the position of fiducial 102 and latch needle 104 on
which fiducial 102 is located.
[0120] FIGS. 9A-9C show schematically the relationship between
positions of fiducial 102 and the intensities of image 130 in the
first and second wavelength bands A region of light sensitive
surface 282 is shown schematically with image 130, in ventral view,
in a view 294 in each of FIGS. 9A-9C. The dividing line of filter
282 is shown as line 296 in view 294. The relative intensities of
image 130 in the first and second wavelength bands are represented
schematically in greatly exaggerated scale and only qualitatively
in proportion to the actual intensities of light in image 130 in
the first and second wavelength bands by the size of arrows 298 and
300 respectively.
[0121] In FIG. 9A fiducial 102 is located on optic axis 278 and
image 130 has the same (appropriately normalized and corrected)
integrated intensity (i.e. integrated over the area of image 130)
in both wavelength bands. Arrows 298 and 300 are shown the same
size. In FIG. 9B fiducial 102 is displaced away from optic axis 278
towards first half 290 of lens 276. Image 130 is displaced from
optic axis 278 in the opposite direction and the integrated
intensity of image 130 increases in the first wavelength band and
decreases in the second wavelength band. Arrow 300 is shown much
larger than arrow 298. Similarly, in FIG. 9C, fiducial 102 is shown
displaced away from optic axis 278 towards second half 292 of lens
276. The integrated intensity of image 130 increases in the second
wavelength band and decreases in the first wavelength band.
[0122] FIGS. 10A-10C schematically illustrate an OPM 150, in
accordance with another preferred embodiment of the present
invention, imaging fiducial 102 of latch needle 104. OPM 150
comprises a fiducial illuminator 152 and a fiducial imager 154
comprising two, preferably identical, detectors 156 and 158.
Fiducial illuminator 152 illuminates fiducial 102 of latch needle
104. Fiducial 102 reflects some of the light incident on fiducial
102 towards each of detectors 156 and 158.
[0123] Detectors 156 and 158 have light sensitive surfaces 160 and
162 (shown greatly exaggerated in thickness for convenience and
clarity of presentation) and lenses 164 and 166 respectively. Lens
160 focuses reflected light from fiducial 102 to provide an image
168 of fiducial 102 on light sensitive surface 160. Similarly, lens
166 provides an image 170 of fiducial 102 on light sensitive
surface 162. Light sensitive surface 160 with image 168, and light
sensitive surface 162 with image 170, are shown schematically, in
ventral view, in views 172 and 174 respectively in each of FIGS.
FIGS. 10A-10C. The intensities of images 168 and 170 are
schematically represented in each of views 172 and 174 by the
length of arrows 169 and 171 respectively. The relative sizes of
arrows 169 and 171 are greatly exaggerated for clarity and ease of
presentation in comparison to the actual relative intensities of
images 168 and 170. Each of detectors 156 and 158 provides a signal
to a controller (not shown) that is a function of the intensity of
reflected light imaged on its light sensitive surface.
[0124] Detectors 156 and 158 are displaced from each other a small
distance, "d", and both are located at a height, "r", directly
above latch needle 104. OPM 150 is oriented with respect to latch
needle 104 so that a line between the centers of lenses 164 and 166
is parallel to latch needle 104. Dashed lines 176 and 178 represent
central rays of light reflected from fiducial 102 into detectors
156 and 158 respectively.
[0125] In FIG. 10A fiducial 102 is located at a point 180 that is
equidistant from detectors 156 and 158. Both detectors receive
substantially the same amounts of reflected light from fiducial
102. Arrows 169 and 171 in views 172 and 174 respectively are
therefore shown the same size. The difference between the
intensities of light reaching detectors 156 and 158 is zero.
[0126] In FIG. 10B fiducial 102 is displaced from point 180 to the
right. As a result of the displacement, the distance from fiducial
102 to detector 158 decreases and the distance from fiducial 102 to
detector 156 increases. This increases the amount of reflected
light reaching detector 158 from fiducial 102 and decreases the
amount of reflected light reaching detector 156 from fiducial 102.
The size of arrow 171 in view 174 is therefore shown much larger
than the size of arrow 169 in view 172. The difference between the
intensities of light reaching detectors 156 and 158, defined as the
amount of light reaching detector 156 minus the amount of light
reaching detector 156, is negative.
[0127] In FIG. 10C fiducial 102 is displaced from point 180 to the
left. This increases the amount of reflected light reaching
detector 156 from fiducial 102 and decreases the amount of
reflected light reaching detector 158 from fiducial 102. In this
case, the size of arrow 171 in view 174 is therefore shown much
smaller than the size of image 169 in view 172. The difference
between the intensities of light reaching detectors 156 and 158, as
defined above, is positive.
[0128] From considerations of geometry it can readily be shown that
when r>>d, if the displacement of fiducial 102 from point 180
is represented by ".DELTA.x", the difference between the
intensities of light reaching detectors 156 and 158 is proportional
to .DELTA.xd/r.sup.4. The difference between the signals sent by
detectors 156 and 158 to the controller, which are functions of the
intensities of reflected light registered by detectors 156 and 158
respectively, can therefore be used to determine .DELTA.x and the
position of fiducial 102.
[0129] FIGS. 11A-11C schematically show an OPM 190, in accordance
with yet another preferred embodiment of the present invention,
imaging fiducial 102 of latch needle 104. OPM 190 comprises a
fiducial illuminator 192 and a fiducial imager 194. Fiducial imager
194 comprises a single detector 196 and two lenses 198 and 200.
Fiducial illuminator 192 illuminates fiducial 102 of latch needle
104. Fiducial 102 reflects some of the light incident on it from
fiducial illuminator 192 towards each of lenses 198 and 200. A
central ray of reflected light from fiducial 102 to lens 198 is
represented by dashed line 202 and dashed line 204 represents a
central ray from fiducial 102 to lens 200.
[0130] Detector 196 comprises a light sensitive surface 206 (shown
greatly exaggerated in thickness for convenience and clarity of
presentation) that is sensitive to light in two non-overlapping
wavelength bands of light. Fiducial illuminator 192 illuminates
fiducial 102 with preferably equal intensities of light from both
wavelength bands. Each of lenses 198 and 200 transmits light in
only one of the two different wavelength bands. Lens 198 focuses
reflected light in one of the two wavelength bands to form an image
214 on light sensitive surface 206. Lens 200 focuses reflected
light in the other of the two wavelength bands to form an image 216
on light sensitive surface 206. Detector 196 sends a first signal
to a controller (not shown) that is a function of the amount of
light in image 214 and a second signal to the controller that is a
function of the amount of light in image 216.
[0131] Lenses 198 and 200 are displaced a short distance from each
other and the line connecting the centers of lenses 198 and 200 is
aligned parallel with and directly above latch needle 104. Assume
that fiducial illuminator 192 is either located equidistant from
lenses 198 and 200, or that any biases in the relative amounts of
light reflected by fiducial 102 onto lenses 198 and 200 resulting
from an asymmetric location of fiducial illuminator 192 with
respect to lenses 198 and 200 are corrected for. Then, when
fiducial 102 is equidistant from lenses 198 and 200, detector 196
registers equal intensities of light for both images 214 and 216
(i.e. surface 206 registers the same intensity of light in both of
the wavelength bands to which it is sensitive). As fiducial 102 is
displaced towards one or the other of lenses 198 and 200, the
relative intensities of light registered for images 214 and 216
changes.
[0132] FIG. 11A shows fiducial light 102 located at a point 208
equidistant from lens 198 and 200. FIGS. 11B and 11C show fiducial
102 displaced right and left respectively of point 208. View 210
each of FIGS. 11A-11C is a ventral view of light sensitive surface
206. View 210 shows schematically images 214 and 216 of fiducial
102 that are formed on light sensitive surface 206 by lenses 198
and 200 respectively. The sizes of arrows 215 and 217 in view 210
represent schematically with greatly exaggerated scale the relative
amounts of light in images 214 and 216 respectively for the
different positions of fiducial 102 shown in FIGS. 11A-11C.
[0133] From considerations of geometry it can readily be shown, as
in the case of OPM 150 shown in FIGS. 10A-10C, that for a
displacement .DELTA.x of fiducial 102 from point 208, the
difference between the intensities of light registered by detector
196 for images 214 and 216 is substantially proportional to
.DELTA.x. The signals sent by detector 206 to the controller, which
are functions of the intensities of light registered by detector
206 for images 214 and 216 can therefore be used to determine
.DELTA.x and thereby the position of fiducial 102.
[0134] FIGS. 12A-12C schematically show an OPM 220, in accordance
with yet another preferred embodiment of the present invention that
is used to measure the position of a latch needle provided with two
fiducials. In FIGS. 12A-12C, OPM, 220 is shown imaging a latch
needle 222 provided with a fiducial 224 and a fiducial 226.
[0135] OPM 220 comprises a fiducial illuminator 228 and a fiducial
imager 230. Fiducial imager 230 comprises a single detector 232 and
a single lens 234 having a lens axis 235. Detector 232 comprises a
light sensitive surface 233 (shown greatly exaggerated in thickness
for convenience and clarity of presentation) that is sensitive to
light in two non-overlapping wavelength bands of light. Fiducial
illuminator 228 illuminates fiducials 224 and 226 preferably with
light having equal intensities in both wavelength bands. Fiducial
224 reflects light in only one of the two wavelength bands and
fiducial 226 reflects light in only the other of the two wavelength
bands. Lens 234 images the reflected light from fiducials 224 and
226 to form an image 236 of fiducial 224 on surface 233 in one of
the two wavelength bands and an image 238 of fiducial 226 on
surface 233 in the other of the two wavelength bands. Detector 232
sends a signal to a controller (not shown) for each of images 236
and 238 that is a function of the intensity of light in the
image.
[0136] Images 236 and 238 have the same intensities, in their
respective wavelength bands, only when fiducials 224 and 226 are
substantially equidistant from axis 235 of lens 234. For different
positions of latch needle 222, one or the other of fiducials 224
and 226 is closer to axis 235. The image of the fiducial closer to
axis 235 is more intense than the image of the fiducial farther
from axis 235. Differences in intensities of images 236 and 238
registered by detector 232 are used to determine the position of
fiducials 224 and 226 and thereby of latch needle 222.
[0137] FIG. 12A shows latch needle 222 in a position for which
fiducials 224 and 226 are equidistant from axis 235. FIG. 12B shows
latch needle 222 in a position in which fiducials 224 and 226 are
displaced to the right of their respective positions shown in FIG.
12A, and FIG. 12C shows latch needle 222 in a position in which
fiducials 224 and 226 are displaced to the left of their respective
positions shown in FIG. 12A. In each of FIGS. 12A-12C, view 240 is
a ventral view of light sensitive surface 234 schematically showing
images 236 and 238. The sizes of arrows 237 and 239 shown in
ventral view 240 represent schematically and in greatly exaggerated
scale, the relative intensities of images 236 and 238 for the
position of latch needle 222 shown in the FIG.
[0138] FIGS. 13A-13C show an OPM 250 imaging fiducial 102, in
accordance with yet another preferred embodiment of the present
invention. OPM 250 comprises a fiducial illuminator 252 and a
fiducial imager 254. Fiducial imager 254 comprises a lens 256
having an optic axis 257 and a detector 258, such as a CCD, having
a pixelated light sensitive surface 260 (shown greatly exaggerated
in thickness for convenience and clarity of presentation). Lens 256
focuses reflected light from fiducial 102 to form an image 262 of
fiducial 102 on pixelated surface 260.
[0139] In OPM 250 the position of fiducial 102 is determined using
the rules of basic optics from the location of image 262 on
pixelated surface 260. FIGS. 13A-13C show schematically the spatial
relationship between the position of fiducial 102 and image 262 of
fiducial 102 on pixelated surface 260. Image 262 and pixels 264 of
pixelated surface 260 are shown schematically in a ventral view 266
of pixelated surface 260 in each of FIGS. 13A-13C. In FIG. 13A
fiducial 102 is located on optic axis 257 and image 262 is located
at the center of pixelated surface 260 shown in view 264 (assuming
lens 256 and detector 258 are aligned). In FIGS. 13B and 13C,
fiducial 102 is displaced to the right and to the left of optic
axis 257 respectively. Image 262 on pixelated surface 260 moves
accordingly to the left and the right of the point at which image
262 is located when fiducial 102 is on optic axis 257.
[0140] Image 262 is preferably focused by lens 256 so that it
covers a plurality of pixels on light sensitive surface 260. Using
methods well known in the art, an optical center of gravity of
image 262 can be defined and located on pixelated surface 260 to
sub-pixel accuracy. Using the location of the optical center of
gravity of image 262, the position of fiducial 102 and latch needle
104 are determined by OPM 250 with an accuracy sufficient for
controlling latch needle actuators in a DDM.
[0141] FIGS. 13A-13C show OPM 250 being used to determine the
position of a single latch needle 104, by imaging a fiducial 102
located on the latch needle 104. However, a single OPM of the form
of OPM 250, in accordance with a preferred embodiment of the
present invention, can be used to determine the position of a
plurality of latch needles 104. This is accomplished by providing
the detector 258 of the OPM with a field of view that includes the
fiducial 102 of each of the plurality of latch needles 104. Each
fiducial 102 of a latch needle of the plurality of latch needles is
imaged on a different rectangular region of pixelated surface 260
of the OPM. As the latch needle 104 on which the fiducial 102 is
located moves back and forth in its operational range of motion,
(indicated schematically by double headed arrow 124) the image of
its fiducial 102 moves back and forth along the length of the
rectangular region of pixelated surface 260 on which it is
imaged.
[0142] For example, in one preferred embodiment of the present
invention, detector 258 is provided with a field of view that
focuses an area of a needle bed having a dimension perpendicular to
latch needles 104 that is on the order of 5 cm. The dimension of
the field of view in the direction parallel to latch needles 104 is
on the order of the operational range of motion of latch needles
104. If the spacing between latch needles 104 in the needle bed is
2 mm the fiducials 102 of 25 latch needles 104 will be in the field
of view of the OPM. Assuming that pixelated surface 260 of detector
258 comprises a square matrix, 5 mm on a side, comprising 512 rows
and 512 columns of pixels fiducials 102 of the 25 latch needles 104
in the field of view of detector 258 are imaged on parallel
rectangular regions of pixelated surface 260 that are approximately
20 pixels wide and 512 pixels long. If the operational range of
motion of a latch needle 104 is on the order of 5 cm, and the
optical center of gravity of the image of a fiducial is located
with a resolution of 0.4 pixels, the position of fiducial 102 and
its latch needle 104 are located with an accuracy of about 40
micrometers.
[0143] Variations of the above-described preferred embodiments will
occur to persons of the art. The above detailed descriptions are
provided by way of example and are not meant to limit the scope of
the invention, which is limited only by the following claims.
* * * * *