Patent GB-803811-A (GB)
Title: Improvements in and relating to electrical apparatus for producing an electric signaldependent on the tension in a continuous linear material
Inventor: ROBINSON JOHN BARDWELL CURGENU
IPC: B65H23/04
Filed: 1954-05-24
Abstract: 803,811. Automatic tension control Systems. ENGLISH ELECTRIC CO., Ltd. May 24, 1955 [May 24, 1954], No. 15203/54. Class 38 (4). [Also in Group XXXVIII] Apparatus producing an electric signal dependent on tension of a continuous linear material passing simultaneously and under tension through two consecutive sections of a treatment plant comprises an engaging member biased against the material and deflected thereby from a datum position in accordance with the tension, and a differential transformer having a movable member deflected from a datum position by the material engaging member in accordance with the tension in the material, such that when a transformer primary is A.C. energized a secondary thereof produces an output voltage representing the tension, and electrical biasing means are provided in circuit with the differential transformer secondary which are adjustable so that the combined transformer and bias output is variable independently of the material engaging member. A steel strip 10 leaves the final stand 11 of a rolling mill and passes over spaced rollers 12, 13 to a coiling reel 14 driven by D.C. motor 15 whose field 15a is energized with current automatically variable in response to the coil diameter. The rollers are disposed so that the strip normally lies above the highest pass line 18 of the mill, and between them a roller 19, rotatable in a cradle 20 swinging about an axis parallel to the roller and controlled by a torsionbar passing through the axis, presses upwardly on the strip so that it is deflected downwards by increasing tension thereof. Arm 20a of the cradle accordingly reciprocates a spring-loaded non-magnetic shaft 24 moving a ferromagnetic core 25 within adjacent coils 27, 28, 29 of a differential transformer 30; coil 28 being energized from winding 33a of an A.C. energized transformer 33 and coils 27, 29 being connected in series opposition. The differential output voltage varying in amplitude and phase sense in response to the deflection of the core from its mid-position is combined with the phase sense and amplitude variable output of a centre-tapped zero-setting potentiometer 35 energized from winding 33c of transformer 33, and applied to a phase-sensitive amplifier 36 whose unidirectional output voltage is proportional in magnitude and sense to deviations from a standard value of tension preset by potentiometer 35, and is measured by indicating instrument 38 calibrated in strip tension. The unidirectional voltage energizes the field winding of an amplifying exciter 37 for the field winding of a Ward-Leonard generator 17 exciting the armature 15b of the reel drive motor 15, whose torque is thus varied to maintain strip tension at the predetermined value; which may alternatively be preset by variation of the mechanical advantage between arm 20a and core 25, or by axially adjusting the positions of the coils 27, 29 relatively to coil 28. An additional A.C. biasing potentiometer (not shown) may be energized from a winding of transformer 33 to introduce a phase sense and amplitude variable voltage into the differential transformer output for compensation of mechanical errors of the system. The roller 19 may be supported at each end by independent pivoted cradle members controlled by independent torsion bars and each displacing the core of an associated differential transformer; the secondary outputs of which may be serially connected to give a cumulative output voltage and opposedly connected over isolating transformers to an indicating device displaying the difference in tension between the two sides of the strip, or connected to a sum and difference indicating device of the kind set forth in Specification 638,941, [Group XXXVIII]. The apparatus is also applicable to the control of tension of strip passing between successive stages of a tandem-rolling mill, or from a reel to a roll. The tension in rubber, paper, or textile webs may be similarly controlled.