US2650986A - Variable sensitivity control device and circuit for use therein - Google Patents

Description

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lSQ-ZOB-R Sept. 1, 1953 P. T. SEMM VARIABLE SENSITIVITY CONTROL DEVICE AND CIRCUIT FOR USE THEREIN 2 Sheets-Sheet 1 Filed June 1, 1950 mmvroa Paul T 56mm CQJM. $5 M 4114 @TToR/v Sept. 1, 1953 Filed June 1, 1950 P. T. SEMM VARIABLE SENSITIVITY CONTROL DEVICE AND CIRCUIT FOR USE THEREIN INVENTOR. Paul 5emm BY CAM f hqdw ATTORNEY5 2 Shets-Sheet 2 Patented Sept. 1, 1953 UNITED STATES PATENT OFFICE VARIABLE SENSITIVITY CONTROL DEVICE AND CIRCUIT FOR USE THEREIN Application June 1, 1950, Serial No. 165,473

4 Claims. (Cl. 250-203) My invention relates to an improved control device having adjustable sensitivity, together with a circuit for use therein.

In control or follow-up mechanism it is desirable to provide low-friction means having great sensitivity to small relative motions and yet adjustable with respect to sensitivity so that varying degrees of inertia, dead band, friction, and other effects in the associated follow-up or control system and varying requirements as to hunting may be taken into account by convenient adjustments after the system is built.

In accordance with the present invention an improved light operated sensing element is provided. This element includes adjustable mechanism which, in one condition of adjustment, gives a high degree of sensitivity limited only by the physical fact that the opaque vane that interrupts the light beam has depth, the light undergoes some unavoidable dispersion, and the lens system can never produce a perfect focal point. As the adjustable element is moved away from this critical position, the sensitivity decreases in accord with the departure from critical.

Further in accordance with the present invention a magnetic amplifier control circuit is provided for use with the sensing mechanism. This control is responsive to the direction and amount of the departure of the control current from a reference value and is characterized by an ability to accommodate itself to slow variation in the control current and may be designed to accommodate control currents of widely varying magnitudes. The control circuit is further characterized by ability to operate effectively with only a single response element (such as a photocell) on the sensing mechanism.

It is therefore a general object of the present invention to provide an improved sensing mech anism imposing small load on the controlling device and having an adjustable sensitivity up to a very high value.

Another object of the present invention is to provide an improved sensing mechanism suitable for use with a follow-up type system.

A further object of the present invention is to provide an improved control circuit responsive to deviations of a control current from a reference value.

Yet another object of the present invention is to provide an improved control circuit responsive to the direction and magnitude of the deviations of a control current from a reference value and using magnetic amplifiers.

' mary 26a of the transformer 20.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in which:

Figure 1 is a schematic diagram illustrating a follow-up mechanism incorporating the features of the present invention;

Figure 2 is a view in perspective of the sensin mechanism of the present invention; and,

Figure 3 is a schematic diagram of the control circuit of the present invention as applied to a different type sensing unit and adapted to drive a two phase alternating current motor.

Referring now to Figure 1, there is shown a follow-up control mechanism operative to produce an indication on the scale S in accord with the temperature differential between the junctions I0 and I2 of the thermocouple T. Briefly, this mechanism includes a sensing element, indicated generally at E, which is driven by the control mechanism C in response to movements of the opaque vane M which itself moves in response to the current flow in DArsenval movement I6 associated with the temperature differential between thermocouples l0 and I2.

The control mechanism C derives energy from an A.-C. voltage source I8 connected to the pri- This transformer has a pair of like secondaries, 20b and 200, which feed the relay windings 22a and 24a of the relays 22 and 2t, respectively. The windings 22a and 24a have a common return circuit to the windings 20b and 200 through the rectifier 260.

The relays 22 and 24, when energized, close their respective contacts 22b and 24b to cause current flow through the respective field windings 26a and 26b of the D.-C. series motor 26,

this current being derived from the battery 28.

When relay 22 is energized the motor 26 1S driven in one direction and when relay 24 is energized, motor 26 is driven in the opposite direction.

The sensing device, indicated generally at E, includes a rotatable carriage 30 upon which is mounted a point source lamp 32 and a photoelectric cell 34. The lamp 32 may be any one of many types well known in the art, a small size, high intensity tungsten filament type lamp being particularly suitable for this purpose. The

3 photo-electric cell likewise may be any one of many well known types, the selenium or "barrier layer cell being especially suitable.

A pair of lenses 36 and 38 are mounted on the carriage 30 to direct the portion of the total light emanating through a preset solid angle area from lamp 32 on the cell 34. These lenses define a focal point 40 which ls substantially in the line of travel of the vane ll. At this point the rays of light that eventually reach the photo cell 34 converge at a single point. As pointed out hereafter, the position of this focal point is adjustable relative to the line of travel of vane ll to adjust the sensitivity of the sensing mechanism.

A mirror 33 is mounted behind the lamp 32 to direct illumination therefrom in the forward direction to lens 18.

The motor 26 is mechanically connected to rotate the carriage 30 in accord with its own rotations. This drive mechanism, shown diagrammatically in Figure 1, may, for example, include a gear train connecting these elements and having a motion step down so that the available torque of motor 26 is stepped up for application to the carriage. Chain, belt, or other drive may be employed.

When the relay 22 is energized and motor 25 rotated in one direction, the carriage 30 rotates in a corresponding direction. When relay 2! is energized, motor 26 rotates oppositely and the carriage 3| rotates in the reverse direction.

The relays 22 and 24 are separately energized in response to the quantity of light incident on photocell 24 by the circuits including magnetic amplifiers 42 and 44. These magnetic amplifiers or saturable reactors each comprise a rectangular magnetic core with a pair of windows defining three legs. Each has a controlled winding (42a and a, respectively) wound on the outside legs, the two parts of each winding being wound in cumulative sense. The center or control leg of each magnetic amplifier carries a pair of windings, one winding of each pair (42b and b of amplifiers l2 and 44, respectively) is a biasing winding to carry relatively constant biasing current. The other winding of each pair (420 and c of amplifiers l2 and H, respectively) is a control winding and carries the control current from the photocell 34.

The biasing windings 42b and b are connected in a series circuit to the D.-C. output terminals of the bridge rectifier 46, the A.-C. input terminals of this rectifier being connected to the tertiary winding 20d of the transformer 20.

The control windings 42c and c are similarly connected in a series circuit with the photocell 34. However, this circuit is poled so that in magnetic amplifier 42 the magnetomotive force of the winding 42c reinforces that of winding 42b while the magnetomotive force of the winding c opposes that of the winding b when current flows in one direction in the circuit. For opposite current flow, the M. M. F. of winding 20 opposes that of winding 42b and the M. M. F. of winding reinforces that of the winding b.

Operation Operation of the system of Figure 1 is as follows. When the temperature differential between thermocouples IO and i2 changes from an initial condition where relays 22 and 24 are not picked up and vane ll interrupts part of the light rays, the current flow in the D'Arsenval movement Ii accordingly changes. This current flow in the coil Ilia gives rise to a change in torque (since the magnetic field between poles lib does not change) and causes the movement to rotate until the restoring torque of spring lSc again equals the torque due to current flow. As the movement rotates, the vane ll (attached to the rotor by the arm l5) swings into or out of the path of the light from lamp 32 and thereby increases or decreases the illumination of the photocell 34.

As the illumination of photocell 34 changes, the output voltage thereof varies and the current flow through the control windings 42C and c is altered. This current flow change causes relays 22a or 24a to be more or less energized in accord with the direction of departure from the neutral or predetermined initial value. However, the relay that is more energized does not pick up until this departure from the neutral current reaches a predetermined quantity determined by the friction and lost motion inherent in the relay units.

When the energized relay picks up the motor 26 is driven in the corresponding direction and the carriage 30 executes rotation in unison therewith. The direction of rotation imparted to the carriage (due to the orientation of field windings 26a and 26b, the arrangement of the drive between motor 28 and the carriage 30, and to the orientation of control windings 42c and He) is such as to drive the carriage in direction to restore the predetermined reference light value on the photocell 34, thereby rotating the canine in amount corresponding to the initial movement of the opaque vane II. The amount of the vane movement (and hence the temperature change) can then be read from the position of the pointer 35 on the scale S.

Sensitivity adjustment The foregoing mechanism, as a follow-up or closed cycle control, inherently deviates slightly from true response as the departure from reference or neutral condition increases. The amount of this departure is determined by the quantity of movement imparted to the carriage 30 for a given movement of the vane I 4. However, inherent time delays, lost motion, and other unavoidable attributes of a physical system place an upper limit on the allowable sensitivity, since they cause undesirable hunting and perhaps even self-excited oscillations.

The sensing mechanism of the present invention, shown in detail in Figure 2, is particularly effective in that it can be adjusted to achieve a wide range of sensitivities to accommodate the unit to a great range of operating conditions. This is accomplished by the movable mount, in-

dicated generally at 48, which provides convenient manual adjustment of the position of the lens 38 along the axis between light 32 and photocel1 34. When the lens is shifted to position vane I4 exactly at the focal point 40 (as shown in Figure 2), the change in illumination of the photocell 34 with a small vane movement is very great and is limited only by the physical facts that the vane l4 has some thickness, the focal point defined by the lenses cannot be perfect, and dispersion is inherent in the optical system. When the lens 38 is shifted to move the focal point 40 away from the path of travel of vane I4, as shown in Figure 1, the amount of light change upon vane movement is reduced, since the cone of light has substantial cross-sectional area in the path of vane travel. The sensitivity of the sensing element is accordingly reduced in accord with the amount of the departure of the focal point from the path of vane travel.

The lens adjusting mechanism 48 comprises a U-shaped support 48a mounted on carriage 30 and carrying a horizontal screw thread shaft 48b, this shaft being rotatably supported by hearings on support 48a. The lens 38 is mounted on a rider 480 which threadedly receives the shaft 48b and has a depending pin 48d extending through the elongated slot 48e on the support 48a. As the handle 48f is rotated to rotate shaft 48b, the rider 48C shifts in response to the screw thread engagement and Shifts the lens 38. The rider 480 is held against rotation by the pin 48d.

The carriage 30, Figures 1 and 2, is supported for rotation about the axis of the fixed vertical shaft 31. As seen in Figure 1, a fixed bushing 39 is mounted on the bottom of this shaft and defines an annular bearing surface upon which rests the bushing 3I (formed unitarily with carriage 30), thus supporting the carriage for rotation about the shaft 31.

The electrical elements on the carriage 30 are energized through loose flexible leads (not shown) which permit free rotation of the carriage over the length of the fixed scale S.

A.-C. motor follow-up Figure 3 shows the circuit of the present invention as applied to an A.-C. motor driven followup system. In this device the sensing mechanism shown in Lang and Cross application S. N. 786,678, now Patent Number 2,576,611, entitled Measuring Apparatus and assigned to the same assignee as the present invention, is used. Briefiy, this apparatus includes a split inductor I mounted on a movable carriage driven by the two-phase induction motor I02. A vane or flag I4 (which may, for example, be a DArsonval movement responsive to the temperature difference between a pair of thermocouples) is of metal and moves relative to this coil, thus altering the impedance thereof.

The motion of the vane I4 and the incident impedance change of the inductor I00 detunes the tuned plate-tuned grid type oscillator defined by the election tube I04 and thereby alters the magnitude of oscillations of the oscillator and the value of the unidirectional space current flow in the tube I04. This unidirectional space current flow is in the form of pulses of low frequency (i. e. 60 cycles), since the cathode-anode space path voltage of tube I04 is obtained from the synchronized A.-C voltage sources I06 and I08.

The quantity of the unidirectional space current flow in the tube I04 varies the voltage drop across the resistance I and thereby controls the cathode-control electrode voltage of the electron tube II2. The electron tube II2 conducts unidirectional space current in low frequency pulses each of magnitude determined by the detuning of the oscillator defined by the tube I04 and hence by the position of vane I4 relative to the inductor I00. The resultant voltage pulses appear across terminals a-b.

The control circuit of Figure 3 embodies a pair of magnetic amplifiers I42 and I44 of construction like reactors 42 and 44, Figure 1. The

control windings I42c and I440 of these reactors are connected in series across terminals a and b and thus carry current of magnitude determined by the position of vane I4.

The controlled windings Inc and Ma or the magnetic amplifiers I42 and I44 are connected in series circuit with the winding I20b-I20c of transformer I20 and the winding I22a-I22b of the transformer I22. A connection including rectifier I26 extends between the common terminal of windings I22a and I22b and the common terminal of windings I20!) and I200.

The primary winding I20a of the transformer I20 is energized from alternating voltage source II8 which is synchronized with the sources I06, I08, and H0 to produce a current wave through each of windings M211 and MM synchronized in phase and frequency with the control current in windings I 420 and I440. The bias windings I42b and I441) are energized from the bridge rectifier I46 which is fed from the secondary winding I20e.

The secondary winding I22d of the transformer I22 is connected to one phase winding I02a of the two-phase induction motor I02. The other phase winding I02b is connected to the additional winding mm of the transformer I20 through the phasing capacitor I2Ia. This capacitor is of such value that current flow through the winding I02b is substantially degrees out of phase with the source I I8 and the current flow in winding I02a.

In the device of Figure 3, the voltage induced in winding I 22d (and the current fiow in the winding I02a) depends on the relative impedances of the windings M21: and MM because the magnetcmotive forces of the windings I22a and H212 are in opposition.

The series circuit formed by the control windings I440 and I42e is so poled that current fiow therethrough produces magnetomotive force opposing that of one bias winding (I42b or M411) and reinforces that of the other bias winding, As described above in connection with Figure 1, this causes the impedance of one of windings I42a and MM to increase relative to the impedance of the other, thereby causing the magnetomotive force of one of windings I220 and I22bto overpower that of the other and produce a corresponding voltage in winding I22d. Moreover, when the current flow in winding I22a exceeds that of winding I22b, the current flow is out of phase with the current produced in winding I02a when the opposite condition exists. The direction of rotation of motor I02 accordingly varies in accord with which of the windings mm and I22b creates the predominant magnetomotive force.

The capacitors I2I serve to tune the windings I22a and I221) to convert the half wave current flow otherwise created by the rectifier I26 to a current which has a more nearly sinusoidal wave form.

The windings I420 and I440, I22a and I222), and I02a and I02b, and the drive between motor I02 and the inductor I00 are so arranged that when the vane I4 moves into the inductor I00 the corresponding movement imparted to the inductor is in direction to pull the inductor away from the vane. Consequently, the inductor I00 follows the motion of the vane and the amount of vane movement may be indicated by a suitable fixed scale between the inductor and the support mechanism (not shown).

The vane I4 may be mounted on any control device whose movement is desired to be recorded.

sure responsive bellows, a Bourdon tube, and so forth.

Moreover, in any of the follow-up systems shown and described herein, anticipation may be used to improve stability of operation without reducing the sensitivity.

It will be apparent that while the transformer windings 20b and 200, Figure 1, and 1201) and I200, Figure 3, derive energy from the same source of alternating E. M. F.. these windings in fact as separate sources of alternating E. M. F. synchronized in phase and frequency.

Each of the magnetic amplifiers or saturable reactors 42, 44, I42, and I acts to produce a net inductance (or inductive impedance) in the controlled winding (1. e. 42a) determined by the net M. M. F. of the control and bias windings (i. e. 42c and 42b, respectively). When this net M. M. F. increases, the resultant flux in the middle leg of the magnetic amplifier returns by way of the outer legs and thereby saturates these legs. The resultant saturation reduces the inductance of the controlled winding. The controlled winding does not cause induced voltage in the controlling or bias windings, since the central leg of each core extends between points of like magnetic potential with respect to the magnetizing effects of the controlled windings.

While I have shown a specific mechanism including a shiftable lens to alter the position of the focal point 40 relative to the path of travel of vane II, it will be understood that other arrangements will work. Specifically, the means may be provided to shift the carriage as a unit and thereby alter the position of the focal point relative to the path of vane travel.

While I have shown and described specific embodiments of the present invention, it will of course be understood that I do not wish to be limited thereto and that many modifications and alternative constructions may be made without departing from the true spirit and scope of the invention. I therefore intend by the appended claims to cover all such modifications and alternative constructions falling within the true spirit and scope thereof.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a follow-up system operative to follow the movements of an opaque vane along a predetermined path and having an adjustable sensitivity, the improvement comprising a movable carriage, a light source and a photo sensitive device on the carriage, means on the carriage operable to direct light from the source to the device, the means directing the light to a focal point substantially in the path of movement of the vane, said means including elements adjustably positioned on the carriage and operative to shift the position of the focal point to provide controlled sensitivity to vane motion, and mechanism responsive to the output of the photo sensitive device operative to move the carriage in the direction of vane movement.

2. In a follow-up system operative to follow the movements of an opaque vane along a predetermined path and having adjustable sensitvity, the improvement comprising a movable carriage, a light source and photosensitive device on the carriage, lens elements on the carriage operable to direct light from the source to the device, the lens elements directing the light to a focal point substantially in the path of movement of the vane, at least one lens element being adjustably positioned on the carriage to vary the location of the focal point in relation to the path of vane movement to control the sensitivity to vane motion.

3. A follow-up mechanism responsive to the movements of an opaque vane along a predetermined path comprising a movable carriage, a light source and light sensitive device on the carriage, means on the carriage directing light from the source to a focal point substantially in the path of movement of the vane and operable to direct light from the source to the device, a pair of magnetic amplifiers each having a bias winding, a control winding and a controlled winding, a pair of synchronized sources of alternating E. M. F., means having a pair of energizing circuits and operative when one circuit is energized to move the carriage in one direction and when the other circuit is energized to move the carriage in the opposite direction, means defining a pair of circuits each including one source, one of the controlled windings and one energizing circult, means defining a circuit through the bias windings, and means defining a circuit from the light sensitive device through the control windings, the last circuit being poled to cause one control winding to oppose the M. M. F. of its associated bias winding and the other control winding to reinforce the M. M. F. of its associated bias winding.

4. In a follow-up system operative to follow the movements of an opaque van along a predetermined path and having an adjustable sensitivity, the improvement comprising a movable carriage, a light source and a photo sensitive device on the carriage, means on the carriage operable to direct light from the source to the device, the means directing the light to a focal point substantially in the path of movement of the vane, elements operable to adjust the position of the focal point relative to the path of travel of the vane to provide controlled sensitivity to vane motion, and mechanism responsive to the output of the photo sensitive device operative to move the carriage in the direction of vane movement.

PAUL T. SEMM.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,976,298 Richter Oct. 9, 1934 1,976,355 Mees et al. Oct. 9, 1934 2,277,849 Fitzgerald Mar. 31, 1942 2,310,955 Hornfeck Feb. 16, 1943 2,319,406 Jones May 18, 1943 2,414,936 Edwards et al. Jan. 28, 1947 2,447,338 Hornfeck Aug. 17, 1948 2,472,019 Kinderman May 31, 1949 2,518,865 Cartotto Aug. 15, 1950 2,524,807 Kallmann Oct. 10, 1950 2,527,797 Cohen Oct. 31, 1950 2,534,769 Hart Dec. 19, 1950 FOREIGN PATENTS Number Country Date 963,598 France Jan. 4, 1950

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