Winch drum cable length measurement apparatus

• US 4,356,557 A
• Filed: 09/27/1979
• Issued: 10/26/1982
• Est. Priority Date: 04/06/1978
• Status: Expired due to Term

• Current Assignee: Varco International Inc. (NOV, Inc.)
• Original Assignee: Cooper Industries, Inc. (Eaton Corporation PLC.)
• Inventors: Terbrack, William H., Bell, Leo A.
• Primary Examiner(s): Krass, Errol A.
• Application Number:
  US06/079,334
• Time in Patent Office: 1,125 Days
• Field of Search: 364/561, 364/562, 235/92 DN, 73/760, 73/783, 73/793, 73/852, 33/126.5, 33/126.6, 33/133, 33/140, 33/142
• US Class Current: 702/163
• CPC Class Codes: G01B 7/026 for measuring length of cable, band or the like, which has been paid out, e.g. from a reel measuring length of objects while moving G01B7/04

Abstract

The invention is an electronic wire length measuring apparatus for accurately measuring and indicating the height of a traveling block above a fixed reference point in oil well drilling applications where a traveling block is hooked to a cable and pulley arrangement and to a winch drum, said winch drum being used to vary the height of the traveling block. The wire length measuring apparatus produces an output visual indication of the height of the traveling block independent of variations in drum size, wire size, number of layers on the drum, and the weight load on the traveling block, which causes a lower actual traveling block position due to stretching in the wire.

Claims

1. An improved wire length measurement apparatus for converting absolute angular position data of a drum motion transducer for a drum wrapped with multiple nested layers of coplanar, substantially round and multiturn wire into an output indication of the position of a traveling block attached to the wire, wherein the output indication is accurate independent of the number of layers of wire, the drum diameter and the diameter of the wire, said apparatus comprising:

(a) summing amplifier means for converting an input signal representing the absolute angular drum position to a wrap signal representing the length (L) of wire wound onto the drum;

(b) a first layer input means for applying an input signal to said summing amplifier representing the number of turns wound onto the first of said nested layers and for setting the gain of said summing amplifier such that said wrap signal represents the length of wire wrapped onto the drum;

(c) an isolation means, connected between the output of said drum motion transducer and the input of said first layer input means, for isolating said drum motion transducer and for producing a turns signal proportional to the output signal of said drum motion transducer and representing the absolute angular position of the drum relative to its position at a given initial setting;

(d) a second layer input means connected in parallel to the first layer input means for varying the gain of said summing amplifier such that when wire has been wrapped onto the second layer, the wrap signal of said summing amplifier represents the amount of wire wrapped onto both the first and second layers;

(e) an additional layer input means for each additional layer of wire to be wrapped for the same purposes as the second layer input means;

(f) a layer activation means connected to the inputs of said second and additional layer input means for activating said second and additional layer input means, thereby changing the gain of said summing amplifier, when the turns signal of said isolation means, representing the absolute angular drum position, indicates that wire is being wrapped onto the second and additional layers seriatem; and

(g) an output means connected between the output of said summing amplifier and the input of an output display for converting the wrap signal of said summing amplifier to an output signal in convenient engineering units for display.

2. An apparatus for measuring the amount of wire wound about a drum in the form of a multilayer, multiturn coil, comprising:

a drum motion detector for providing a signal representing the angular position of the drum with respect to a reference position;

multiplication means for multiplying the output signal of the drum motion detector by a predetermined constant and providing as an output a wrap signal representing the length of wire wrapped onto the drum, wherein the multiplication means includes a summing amplifier having an input resistance which receives the signal from the drum motion detector; and

first modification means for detecting when each new coil layer is being wrapped onto the drum and changing the value of said predetermined constant to compensate for an increase in the diameter of the turns of the coil for each new layer, thereby increasing the accuracy of the wrap signal, wherein the first modification means includes a plurality of resistances which may be selectively connected in parallel with the input resistance to thereby vary the gain of the summing amplifier.

3. An apparatus for determining the position of an article connected to a wire wound about a drum in the form of a multilayer, multiturn coil, comprising:

a drum motion detector for providing a signal representing the angular position of the drum with respect to a reference position;

multiplication means for multiplying the output signal of the drum motion detector by a predetermined constant and providing as an output a wrap signal representing the length of wire wrapped onto the drum, wherein the multiplication means includes a summing amplifier having an input resistance which receives the signal from the drum motion detector;

first modification means for detecting when each new coil layer is being wrapped on to the drum and changing the value of said predetermined constant to compensate for an increase in the diameter of the turns of the coil for each new layer, thereby increasing the accuracy of the wrap signal, wherein the first modification means includes a plurality of resistances which may be selectively connected in parallel with the input resistance to thereby vary the gain of the summing amplifier;

a stress detector for providing a signal representing the amount of force applied to the wire; and

second modification means for changing the value of said predetermined constant as a function of the stress detector signal, whereby the wrap signal will correspond to the actual position of the article despite stretching of the wire, wherein the second modification means includes a stress compensation amplifier which receives the signal from the stress detector and generates a stretch compensation signal which is applied to the input of the summing amplifier.