US2825861A - Integrating servo mechanism - Google Patents

Description

March 4, 1958 M. WEINSTEIN INTEGRATING SERVO MECHANISM Filed Dec. 22, 1955 CONTROL CURRENT D. C. 6 EN ERATOR.

United States PatentOfiice 2,825,851 Patented Mar. 4, 1958 INTEGRATING SERVO MECHANISM Mark Weinstein, Bronx, N. Y., assignor to Emerson Radio & Phonograph Corporation, Jersey City, N. J., a corporation of New York Application December 22, 1955, Serial No. 554,655

6 Claims. (Cl. 318327) This invention comprises an improved form of integrating servo mechanism.

An important object of the invention is to provide an integrating servo mechanism employing a magnetic amplifier.

An important object of this invention is to provide a system of this type which does not employ vacuum tube amplifiers.

A further object of the invention is to provide an integrating servo mechanism employing a magnetic amplifier whose output voltage is determined by the control current which sets the saturation level of the amplifier.

Another object of this invention is to provide a similar system in which an independent control is provided to set the magnetic saturation level of the magnetic amplifier.

Another object of the invention is to provide a simple and rugged integrating servo mechanism which for most uses is independent, as to accuracy, of changes in temperature.

Other and more detailed objects of the invention will be apparent from the following description of the embodiment of the invention illustrated in the accompanying drawings.

In the drawings,

Figure 1 is a diagrammatic and schematic illustration of one form of mechanism employing the principles of this invention;

Figure 2 is a graphic illustration of an adjustment of the magnetic amplifier to provide an operating characteristic illustrated thereby; and

Figure 3 is a diagrammatic illustration of a modified form of the invention.

The system as illustrated in Figure 1 includes a magnetic amplifier illustrated generally at 10, having a high turn primary winding 12, a bias or control winding 34-, and an output or secondary Winding 16, all magnetically associated with a magnetic core, as illustrated. The open ating or signal voltage B is applied to the input terminals 18 and 20. This system is most efiicient for signal voltages E which vary slowly enough so that the related response of the A. C. output of the system remains sinusoidal. The terminal 18 is connected to one end of the primary 12. The terminal 26 is connected to one end of the armature Winding 22 of the tachometer 2 and its other terminal is connected to the remaining terminal of primary winding 12. Preferably the tachometer is provided with a permanent magnet field structure 26. The armature 28 of the tachometer, which in use operates as a direct current generator, has its shaft connected to the shaft of the armature 34 of the motor 32, as indicated by the connection Sill. The motor 32 is a two phase motor having the field windings 36 and 38. The field winding 36 is energized from an alternating current source at suitable voltage and fixed frequency. The quadrature field winding 33 is connected in series with the secondary 1d of the magnetic amplifier. This circuit portion is also energized from a suitable source of alternating current of fixed frequency.

The magnetic saturation level of the magnetic amplifier in the form of the invention shown in Figure l, is determined by means of the control Winding 14, which is energized through a variable resistor 40 from a suitable direct current source. Those skilled in the art will understand from the above that the magnetic amplifier output voltage 13 is determined by the control current which sets the saturation level. The control current in this case being supplied through the adjustable resistor 49. The output voltage l3 drives the two phase servomotor 32, which in turn drives the connected D. C. tachometer 2d. The connection of the armature 22 into the control circuit is made so that the D. C. output voltage E of the tachometer is fed into the control circuit to buck the signal voltage E applied to the terminals 18 and it will be understood that the control current is equal to the difference between the signal voltage and the tachometer voltage divided by the resistances in the control circuit.

Referring to Figure 2, there is illustrated the fact that the magnetic amplifier may be adjusted by means of the resistor 48 to give any desired type of characteristic such as that shown. In the case shown, the output voltage E between the point C and D can be maintained with control current of between +-A and -B. In practice A and B can be held to less than it) microamperes. if the control circuit resistance is kept low, a very small difierence in signal voltage and tachometer voltage is required to set the operating point desired. With very small current values for A and B voltages will be approximately equal and the tachometer voltage will substantially follow the signal voltage. This close equality of voltages will occur until at the point D the output is not sutlicient to drive the motor and the tachometer at a fast enough speed to produce a tachometer voltage equal to the impressed signal voltage.

As will be well understood, the reference voltage phasing of the motor 32 can be adjusted so that it will not turn at a value lower than C.

Since the tachometer output is proportional to its speed of rotation the motor speed will be proportional to the signal voltage E Mathematically,

1 ofEat It will be apparent that the motor angle integrates the signal voltage. That is for each change in the signal voltage the added increment of forward movement of the shaft 30 will be cumulative. It is, or" course, assumed that the signal voltage will change at a slow enough speed to enable the system to respond, that is follow these changes. As will be well understood, t e accuracy of the system will be determined by the linearity characteristics of the tachometer but this can be accurately specified and incorporated in the tachometer.

In the modified system of Figure 3, the main difference is that the special control winding 14 has been eliminated and the adjustable resistor ill has been included in the input or control circuit. In this case, as will be well understood, the voltage output of the netic amplifier is determined by the control current which sets the saturation level of the magnetic amplifier. The operation of the circuit is otherwise the same as that previously described.

The important advantage of this system is the elimination of a need for vacuum tubes and their adjuncts. Furthermore, the system has only for its moving parts the servomotor 32 and the tachometer 2 Such a system is reliable and rugged, and requires little servicing, which if necessary is not difiicult to provide. The overall accuracy of the system is determined mainly by the accuracy of the tachometer, and unless the system, accuracy must be extremely close to the tachometer accuracy, it requires no temperature compensation. With the proper design of components the time response of the system can be made very short, so that the system is not limited to slow changes in input signal voltage.

Those skilled in this art will readily appreciate that some changes in the details of the system can be effected without departing from the novel combinations herein disclosed. It is preferred, therefore, that the disclosure be taken as exemplary and that the protection ar'lorded hereby be determined solely by the appended claims.

What is claimed is:

1. An integrating servo mechanism comprising a ma netic amplifier having an output circuit, a motor connected in said output circuit, a D. C. generator driven by said motor, an input circuit for said amplifier fed by said generator in opposition to a slowly varying D. C. signal voltage applied to the input circuit, and means for establishing the saturation level of said amplifier for operation at low current values.

2. In the combination of claim 1, said magnetic amplifier having a high turn primary in its input circuit, a

winding in its output circuit and said saturation establishing means comprising a third-winding connected to means for varying the current therein.

3. In the combination of claim 1, said saturation establishing means comprising means in said input circuit for varying the control current in said circuit.

4. In the combination of claim 1, said motor being a two phase motor having one Winding connected in the output circuit of the amplifier and another Winding fed from a fixed frequency alternating current source.

5. in the combination of claim 1, said motor comprising a two phase motor having one winding in said output circuit and both windings fed from a fixed frequency current source.

6. in the combination of claim 1, saidmagnetic amplitier ving a high turn primary with respect to the secondary.

References Cited in the file of this patent UNITED STATES PATENTS 2,ll5,086 Riggs Apr. 26, i938 2,481,311 Jones et al. Sept. 6, 1949 2,513,537 Williams July 4, 1950 2,729,772 Perkins Jan. 3, 1956

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