Textiles: knitting – Independent-needle machines – Circular
Reexamination Certificate
2000-06-21
2001-06-19
Worrell, Danny (Department: 3741)
Textiles: knitting
Independent-needle machines
Circular
Reexamination Certificate
active
06247338
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to knitting machines, and in particular to selectors which select which latch needles of a knitting machine are activated in the process of knitting a fabric.
BACKGROUND OF THE INVENTION
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 flat needle generally with a long shaft having, at one end, a small hook with a latch, which latch swivels to open and close the hook.
Generally, in a modem knitting machine, many thousands of latch needles are accurately positioned and maintained in a closely packed parallel array. In the process of knitting a fabric, an activation station activates latch needles by moving them forwards and backwards, parallel to their lengths, so that the hook ends of the activated latch needles move towards and away from threads being woven into the fabric. As a latch needle is moved forwards and backwards, its latch swivels back and forth to alternately open and close the latch needle hook so that the latch needle can catch and hold one of the threads being woven into the fabric, pull it to create a loop of fabric, and then release the thread to repeat the cycle.
In rotary knitting machines the needles in an array are held in a cylindrical geometry and rapidly moved, in a rotary motion, into and out of the activation station. Depending upon the fabric being knitted, different ones of the needles moving through the activation station are activated. In linear knitting machines, latch needles are held in parallel slots in large flat needle beds. The activation station is a type of shuttle that moves rapidly back and forth over the needle bed, activating needles appropriate to the weave of the fabric being knitted.
In both rotary and linear knitting machines, a device called a “selector” determines (hereafter referred to as “selects”) whether a needle in the activation station of the knitting machine is to be activated or not. To prevent a needle from being activated, the selector presses on a small protuberance (hereafter referred to as an “activation fin” or “fin”) on the shaft of the needle. When pressure is applied to the activation fin by the selector, the needle moves away from an activating mechanism of the activator station and is “deactivated”. If the selector does not press on the activation fin, the needle is activated.
The selector presses on the fin of a needle, to deactivate the needle, with a “selector foot”. The selector foot has two operational selection positions. In a deactivate selection position, the selector foot presses on the fin of the needle thereby preventing the needle from being activated when the needle passes through the activation station. In an activate selection position, the selector foot does not press on the fin of the needle, thereby allowing the needle to be activated when the needle passes through the activation station. The selector foot is generally switched between the selection positions by displacing the selector foot by a small linear translation or by rotating the selector foot through a small angle.
When a knitting machine is operating, the selector of the knitting machine is set to an appropriate selection position for each latch needle that passes through the activation station of the knitting machine. If the selection positions for two needles that pass consecutively through the activation station are not the same the selector has to be switched from one selection position to the other. Prior art selectors generally use solenoids or piezoelectric bimorph actuators to effect the displacements necessary to switch a selector foot between selection positions. However, using these types of actuators, the time it takes to switch a selector foot between selection positions is too long to match the rate at which modern knitting machines move needles through activation stations.
In order to improve the speed with which prior art selectors operate, prior art selectors generally comprise a multiplicity of selector feet which are operated in parallel. In a selector operating with one selector foot, a decision to switch or not switch the selection position of the selector foot, hereafter referred to as “setting” the selector foot, has to be made and executed for every needle that moves through an activation station. In a selector with N activation feet on the other hand, each foot has to be set once for every N needles that move through the activation station. If the switching time needed to switch a selector foot between selection positions is &tgr; secs, a selector with one foot can select 1/&tgr; needles/sec, or equivalently, operate at a “decision” frequency of 1/&tgr; Hz. A selector with N selector feet in parallel on the other hand, can select N/&tgr; needles/sec, i.e. operate at a decision frequency of N/&tgr; Hz. Switching times for prior art activation feet are on the order of 10 msecs. By operating approximately 10 activation feet in parallel, prior art selectors are able to operate at decision frequencies of up to about 1000 Hz.
The decision frequencies at which prior art selectors operate limit the rate at which needles can be moved through a knitting machine activation station and therefore limit the rate at which fabric can be produced. In order to increase the rate at which knitting machines produce fabric, it is desirable to have selectors that can operate at frequencies higher than 1000 Hz.
SUMMARY OF THE INVENTION
It is an object of some aspects of the present invention to provide a selector for knitting machines that can operate at decision frequencies substantially higher than 1000 Hz.
A selector, in accordance with a preferred embodiment of the present invention, achieves decision frequencies higher than those of conventional selectors by decreasing the switching time of selector feet comprised in the selector to less than the switching times of selector feet in conventional selectors.
When in operation, a selector foot constantly switches back and forth between selection positions at a rapid rate. When switching between selection positions, the selector foot generally moves a distance of about 2 mm in about 10 msecs. This change is resisted by friction, forces arising from part wear, machine design and tolerances, and random motional forces that occur during machine operation. The sum of these forces is on the order of between 0.2 and 0.5 Newton. Because of the close spacing within modem knitting machines and the small sizes of many of their components there is little room available for motors or actuators to provide the work required to accomplish the switching. An actuator or motor that can be used to improve the switching time of a selector foot in a selector must therefore be small, capable of switching direction rapidly and able to provide work at a greater rate than that available from motors or actuators in conventional selectors.
Piezoelectric motors can be produced that are small and powerful for their size and that can provide large accelerations of moveable elements in directions which can be reversed in time periods of microseconds. The switching time of a selector foot can be reduced to less than the switching times of selector feet in conventional selectors by using an appropriate piezoelectric motor to switch the selector foot between selection positions, in accordance with a preferred embodiment of the present invention. A selector foot, in accordance with a preferred embodiment of the present invention, is coupled to a piezoelectric motor that can displace a moveable element at a rate of about 400 mm/sec against a force opposing the motion which is on the order of from 0.2 to 0.5 Newton. Preferably, the selector foot comprises a friction coupling surface region suitable for friction coupling with the piezoelectric motor. Preferably, the selector foot is coupled to the piezoelectric motor by resiliently pressing a surface region of the piezoelectric motor, or an appropriate hard friction nub atta
Ganor Ze'ev
Rafaeli Izhak
Ferster & Company Patent Attorneys Ltd.
Nanomotion
Worrell Danny
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