Textiles: weaving – Weft manipulation – Weaving with stationary weft supply
Reexamination Certificate
2000-09-25
2001-08-07
Falik, Andy (Department: 3765)
Textiles: weaving
Weft manipulation
Weaving with stationary weft supply
Reexamination Certificate
active
06269844
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a device and a method for controlling the weft winding arm in weft feeders for weaving looms.
Conventional weft feeders are devices which comprise a fixed drum on which a weft winding arm, which rotates around the drum, winds in a fishing-reel fashion a plurality of turns of yarn which constitute a weft reserve. The turns unwind from the drum of the feeder, when requested by the loom, at each weft insertion, and the weft winding arm, under the control of a supervisor microprocessor, rewinds the turns in order to restore the weft reserve.
Currently, the motor most widely used for the movement of the weft winding arm is of the asynchronous three-phase type. This choice is essentially dictated by the inherent characteristics of these motors and mainly by their low manufacturing and maintenance costs, which are allowed by their simple and sturdy structure and by the complete lack of elements in mutual sliding contact.
Moreover, the evolution of semiconductor technology has provided supervisor microprocessors which integrate peripheral units capable of directly generating the waveforms of the control signals for the inverter that drives such motors, where the term “inverter” is used to designate the driving device capable of generating a system of multiphase sinusoidal voltages with freely variable amplitude and frequency.
However, although the asynchronous motors are satisfactory in performance/cost terms, they suffer considerable drawbacks which limit the performance, especially in application to the movement of the weft winding arm of weft feeders.
The main drawback is the impossibility to achieve simple and effective control of the torque delivered by the motor. To do this, it is in fact necessary to resort to sophisticated control systems of the vector type which however, due to their complexity and to their high computing power requirements, are not adapted to be installed at low cost in weft feeders. Accordingly, it is necessary to renounce to these expensive and complicated control systems and to assume an open-loop system for the adjustment of the speed of the motor, i.e. the synchronization speed set by the inverter is chased by the motor.
In this manner, however, it is impossible to obtain high dynamic performance from the motor, and this is a severe drawback if the weft winding arm of the weft feeder is required to perform high accelerations and decelerations, as occurs increasingly often as a consequence of the continuous increase in the weaving speed.
Moreover, with the open-loop adjustment system the current absorbed by the motor is often significantly higher than the current that is actually necessary; accordingly, the power absorbed in excess is dissipated as heat, is and this causes harmful overheating of the motor and of the electronic components of the power section of the inverter.
SUMMARY OF THE INVENTION
The aim of the present invention is essentially to eliminate these severe drawbacks, and within the scope of this general aim the invention has the following particular objects:
to provide a device and a method for the movement and control of the rotation of the weft winding arm of weft feeders which are simple and reliable in their concept and structure, in particular free from errors and uncertainties in operation and capable of rapidly adapting the operating criteria of the weft winding arm to the requirements of the loom and more generally to the rapid variations of the parameters of the weaving process;
to provide a control and movement device and method as specified which are adapted to allow in particular, an efficient adjustment of the torque that actuates the weft winding arm, so as to allow rapid accelerations and decelerations of the arm;
to provide a device and a method for moving and controlling the weft winding arm of a weft feeder by using, as signals which are significant for driving the entire control system, the signals produced by at least part of the sensors that are already present in the weft feeder.
In order to achieve this aim, these and other objects which will become better apparent hereinafter from the following detailed description, the present invention relates to a method and a device for controlling the rotation of the weft winding arm of a weft feeder, having the specific characteristics stated in the appended claims.
Substantially, according to the invention, a movement and control device is provided in which the weft winding arm is moved by a switched-reluctance electric motor, whose speed is controlled by a first closed-loop adjustment system. The first system comprises a logic block which, by processing the pulsed signals of a first sensor or group of sensors for detecting the speed of the arm and of a second sensor or group of sensors for detecting the passage of the turns of weft that unwind from the feeder, obtains a datum which represents the reference variable of the feedback loop, the reference variable corresponding to the rotation rate that the winding arm must assume in order to correctly restore the weft turns. A second system, also of the closed-loop type, is provided in order to control the torque delivered by the reluctance motor and is substantially adapted to adjust the value of the current circulating in the phase that is active and switched at the instant being considered, the torque being proportional to the square of the phase current.
REFERENCES:
patent: 4716943 (1988-01-01), Yoshida et al.
patent: 5016680 (1991-05-01), Mitsuya et al.
patent: 5857496 (1999-01-01), Brown et al.
Gotti Luca
Pedrini Giovanni
Zenoni Pietro
Falik Andy
Josif Albert
L.G.L. Electronics S.p.A.
Modiano Guido
O'Byrne Daniel
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