Electricity: motive power systems – Constant motor current – load and/or torque control
Patent
1994-01-26
1996-02-27
Shoop, Jr., William M.
Electricity: motive power systems
Constant motor current, load and/or torque control
318 6, 242250, 242390, 242225, H02P 700
Patent
active
054951577
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a cable reeling system particulary for a mobile installation suitable for use in reeling-in and paying-out cables, for example power cables, which should not be subjected to a high tensioning force. A typical mobile installation might be, for example a crane on a dockside.
Hereinafter, the term `reel` should be construed widely to include drum/spool-shaped reels as well as for example a mono-spiral reel.
The ideal mobile cable reeling system should reel-in and pay-out the cable under the minimum tension necessary to lift and safely wind the cable on to the reel, without generating slack when the installation stops. Furthermore, the reel should be able to respond effectively to changes in installation velocity and acceleration/decceleration.
DESCRIPTION OF THE PRIOR ART
For static installations, it is known to measure the tension in a cable for example by use of dancer rollers in the paper and strip-winding industries, but these usually take place in clean controlled conditions and are inadequate, for example, for measuring the tension of a 50+mm diameter cable on a dockside subject to sub-zero temperatures.
Accordingly, it is common to employ in a mobile cable reeling applications a form of constant torque device which is capable of delivering a set torque to the reel regardless of the required forward or reverse speeds. Various types of drive have been used and proposed for example torque motors, permanent magnet hysteresis couplings, electromagnet hysteresis couplings, dry friction clutches and wet friction clutches. These systems are usually high speed/low torque in nature and, therefore, require a gearbox to produce a high torque/low speed output. It is usually necessary to use a high efficiency gearbox such as a helical bevel gear box so as to minimise the reverse driving losses associated with the lower efficiency gear boxes and consequentially avoid the torque experienced by the reel on pay-out being higher than on recovery.
Accordingly, it is an object of the present invention to provide a reeling system for use in conjunction with a mobile installation which is able to apply a constant torque to the reel, independently of system losses, such as, for example, backwinding losses in a low performance gear box like a worm drive gear box.
SUMMARY OF THE INVENTION
The present invention provides a reel system for use in conjunction with a mobile installation comprising an AC motor which drives a reel via reduction means, the reel system further comprising sensing means operable to provide a signal representative of the position of the motor shaft, and a controller, which receives said signal, and is operable to vary continually the stator current of the motor in response to the operating conditions pertaining at a given instant to provide a required torque at the motor shaft.
Reduction means is preferably in the form of a gear box.
Sensing means may be in the form of a positional encoder.
The signal is compared with a reference signal to calculate a torque demand signal, which is used to calculate said stator current.
Preferably controller provides the stator current of the motor such that the required torque at the motor shaft is constant.
The reel may be mounted on the mobile installation and connected to the base station via a cable mounted on the reel.
Alternatively, the reel may be mounted on the base station and connected to the mobile installation via a cable mounted on the reel.
The controller may select a system correction factor in response to the direction of movement of the reel.
The required torque may be varied as a function of the amount of cable on the reel.
It is an advantage of the present invention, that it is possible to use lighter cable than was possible even using a high efficiency gear box, like a helical bevel gear box, because of the improved tension control.
BRIEF DESCRIPTION OF THE DRAWINGS
Exemplary embodiments of the invention will now be described with reference to the accompanying drawings, in which:
FIG. 1 shows a
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Dade Malcolm J.
Richards Marcus
Masih Karen
Metool Products Limited
Miller Austin R.
Shoop Jr. William M.
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