US3798077A

US3798077A - Method for aligning mechanical filters

Info

Publication number: US3798077A
Application number: US00183423A
Authority: US
Inventors: A Gunther
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1971-09-24
Filing date: 1971-09-24
Publication date: 1974-03-19
Anticipated expiration: 1991-03-19

Abstract

In a mechanical filter, the coupling elements coupling the individual filter resonators to each other comprise a material having a Young''s modulus dependent upon the final heat treatment temperature. In a method for aligning the filter, the coupling elements are subjected to heat treatment, the maximum temperature of which is higher than the final heat treatment temperature.

Description

United States Patent [191 1 Giinther 1 Mar. 19, 1974 METHOD FOR ALIGNING MECHANICAL FILTERS [75] Inventor: Alfhart Giinther, I-Iaar, Germany [73] Assignee: Siemens Aktiengesellschaft, Berlin and Munich, Germany 22 Filed: Sept.24, 1971 21 Appl.No.: 183,423

[52] US. Cl 148/13, 148/127, 148/134, 148/154 [51] Int. Cl. C21d l/00, C22f 1/00 [58] Field of Search 148/13, 127, 134, 154; 75/65 EB [56] References Cited UNITED STATES PATENTS 3,547,713 12/1970 Steinemann et al. 148/13 2,342,274 2/1944 I-Iecht 148/134 3,499,804 3/1970 Clarke 3,364,087 l/l968 Solomon et a] 75/65 EB Primary ExaminerRichard 0. Dean Attorney, Agent, or Firm-Herbert L. Lerner [5 7] ABSTRACT In a mechanical filter, the coupling elements coupling the individual filter resonators to each other comprise a material having a Youngs modulus dependent upon the final heat treatment temperature. In a method for aligning the filter, the coupling elements are subjected to heat treatment, the maximum temperature of which is higher than the final heat treatment temperature.

5 Claims, 5 Drawing Figures comm DEVICE PATENTEDMARIQIQM 3,798,077

SHEET 1 OF 3 Fig. 1

Fig. 2

MUDULUS E OF 185 o I 3 o THERMELAST 1 I I I I I I TEMPERATURE TIN C FATENTEDMAR 1 9 T974 3.798.077

sum 2 [IF 3 0,03- RELATIVE CHANGE OF YUUNG'S []I[]2 MUDULUS r i 1 i [000 50E] BUU TEMPERATURE TIN C PATENTEDMAR 19 m4 3,798,077

SHEEI 3 [1F 3 EUNTROL DEVICE Fig. 5

@AIGHT SUURCE15 [LL15 23 N Kn I N1 METHOD FOR ALIGNING MECHANICAL FILTERS The invention relates to a method for aligning mechanical filters. More particularly, the invention relates to a method for aligning mechanical filters in which the coupling of the individual filter resonators is achieved via coupling elements comprising a material having a Youngs modulus which depends upon the temperature of the final heat treatment.

As is well known, mechanical filters consist of several mechanical resonators which are mutually coupled to each other via one or more coupling elements. The end resonators are usually designed as electromechanical transducers for transforming electrical oscillations into mechanical vibrations or for transforming mechanical vibrations into electrical oscillations. A type of steel having a temperature coefficient of expansion as low as possible is usually utilized as the resonator material. A1- most any metallic material is suitable for use as the coupling elements. Generally, however, the same material is utilized for the coupling elements and the resonators.

Due to unavoidable manufacturing tolerances and structural inhomogeneities occurring in the material of the coupling elements and the resonators, a filter of the aforedescribed type does not immediately acquire the required transfer characteristic. It is therefore necessary to suitably compensate for errors in material and manufacture. As is well known, the process of compensation is known as the aligning of the filter. In order to obtain the proper transmission characteristic, it is not only essential that the resonant frequency of the individual resonators be at relatively exactly preset frequencies, but it is also important to adjust the degree of coupling to the correct value which comes as close as possible to the theoretical value. Although it is possible to reduce the coupling, for example, by removing material from the coupling elements, the error which results from the removal of too much material cannot be reversed with any economically justified effort.

The principal object of the invention is to provide a method for aligning mechanical filters which particularly assures the correct adjustment of the coupling elements and with which, in particular, a subsequent increase of the coupling factor is possible.

An object of the invention is to provide a method for aligning mechanical filters which is automatic in order to assure an adjustment process which is as efficient as possible.

An object of the invention is to provide a method for aligning mechanical filters which is simple in nature and functions with efficiency, effectiveness and reliability.

The method of the invention starts with a method for aligning mechanical filters in which the coupling of the individual filter resonators is accomplished via coupling elements comprising a material having a Youngs modulus depending upon the final temperature of the heat treatment. In accordance with the invention, the coupling elements are subjected to a heat treatment, the maximum temperature of which is higher than the final temperature of the heat treatment, or the precipitation temperature.

It is particularly preferable, in accordance with the invention, to carry out the heat treatment in a manner whereby the Youngs modulus of the coupling elements is increased.

In accordance with my invention, the material of the coupling elements preferably comprises groups of materials which exhibit an anomaly of their Youngs modulus as a function of the temperature. Such groups of materials are, for example, nickel-iron alloys, in which additions of other, particularly metallic, materials are included. A suitable material of such type is known, for example, by the tradename Thermelast and is produced by the Vacuumschmelze Company of West Germany. As a function of the final heat treatment temperature, which is also known as the precipitation temperature, these materials have a Youngs modulus which initially increases with temperature and, after passing a maximum magnitude with increasing heat treatment temperature, decreases. The individual curves for the same material differ quantitatively only by the degree of cold working to which the material was subjected prior to the final thermal treatment.

In order that the invention may be readily carried into effect, it will now be described with reference to the accompanying drawings, wherein:

FIG. 1 is a circuit diagram of the equivalent electrical circuit of a coupling element of a mechanical filter;,

FIG. 2 is a graphical presentation of the dependence of the Young's modulus of Thermelast on the temperature, the parameter of the curves being the degree of cold working of the Thermelast;

FIG. 3 is a graphical presentation of the relative variation of the Youngs modulus of Thermelast referred to an original final temperature of heat treatment of 400C;

FIG. 4 is a schematic diagram and circuit diagram of an embodiment of apparatus for localized heating of a coupling element of a mechanical filter in accordance with the method of the invention; and

FIG. 5 is a schematic diagram illustrating another embodiment for heating a coupling element of a mechanical filter in accordance with the method of the invention.

In accordance with the analogy of electromechanical force to current, the equivalent electrical circuit of a short coupling element, having a length which is less than M8 wavelength, when A is the wavelength of the material, may, as shown in FIG. 1, be represented by a 12' circuit comprising capacitances C in the shunt arms and an inductance L in the series arm. For a coupling element which provides longitudinal vibrations or oscillations, for example, having a length a, a crosssectional area F, a Youngs modulus E, a mass m and a normalized frequency (.0

L A aw /EF and C A m/Z Only the inductance L is important for the mechanical coupling factor. For a variation AL of the inductanee L,

wherein AE is the variation of Youngs modulus.

In FIG. 2, the abscissa represents the temperature T in C and the ordinate represents the Youngs modulus E of Thermelast. As shown in FIG. 2, the Youngs modulus initially essentially increases with increasing temperature and reaches its maximum at approximately 500 to 600C, depending upon the degree of cold working of the Thermelast. In FIG. 2, curve 1 represents Thermelast having a degree of cold working of percent, curve 2 represents Thermelast having a degree of cold working of 31 percent and curve 3 represents Thermelast having a degree of cold working of 50 percent.

In FIG. 3, the abscissa represents the temperature T in C and the ordinate represents the relative change or variation of Youngs modulus, referred to at original final treatment temperature of 400C. That is, the magnitude may be read directly at the ordinate of FIG. 3. Curves l, 2' and 3 of FIG. 3 are obtained from the curves 1,

v 2 and 3 of FIG. 2, and represent 0%, 31% and 50% degrees of cold working of the Thermelast, as in FIG. 2.

As shown in FIG. 3, for an initial final heat treatment temperature of 400C, a variation of Youngs modulus of up to 4% may be provided by subsequent heat treatment, depending upon the degree of cold working, if the final heat treatment occurs at a temperature between 400 and 600C. In accordance with the aforedescribed equations, a variation of the coupling may thus be provided in the same order of magnitude if the coupling elements comprise a material having a Youngs modulus which depends upon the final heat treatment temperature. It is only necessary that care be taken that the maximum temperature utilized for varying the Youngs modulus is higher than the initial final heat treatment temperature or precipitation temperature. This method is preferably utilized if the coupling is to be increased. It is also applicable, as shown in FIG. 2, however, if the coupling is to be decreased, and especially if the heat treatment occurs at a temperature at which the maximum of the variation of the Youngs modulus has already occurred. Since the variations or changes of the coupling provided by my method are in the order of magnitude of 3 to 4 percent, a relatively accurate adjustment may be obtained even if the properties of the material and the tolerances occurring during manufacture have relatively high values.

FIG. 4 is a schematic diagram of apparatus for providing the method of the invention. The apparatus of FIG. 4 heats the individual coupling elements by direct current. A mechanical filter is illustrated schematically in FIG. 4 and comprises a plurality of resonators 5, in front view, mutually coupled via a coupling element 6. The coupling element 6 extends beyond the end resonators in order to indicate that additional resonators may be included in the filter.

In FIG. 4, the coupling factor between the first and second resonators 5, running from left to right, is K The coupling factor between the second and third resonators 5, running from left to right, is K The coupling factor between the third and fourth resonators 5, running from left to right, is K If contact electrodes 7 are placed on the coupling element 6 and are energized by a voltage source 8, said coupling element is locally heated and only the coupling factor K is varied thereby.

The heat provided by the electrical current may be adjusted by a suitable control device 9 connected in series with a current-controlled resistor I0.'The method may be made automatic by, for example, providing a temperature sensor 11 at each area of the coupling element to be adjusted. The temperature sensor 11 may control the resistor 10 via a suitable control device 12 and electrical connecting leads 13 which connect said control device to said resistor.

Another arrangement for heat treating the coupling elements in accordance with the method of the invention, is shown in FIG. 5. In the apparatus of FIG. 5, a light source 15 functions as the heat source. The light provided by the light source is of sufficient density and sufficiently high color temperature. The heat source 15 may also be a laser. If the heat source 15 is a light source, a focusing arrangement 16 may be provided in order to provide localized heating of the coupling element 6.

Thus, for example, as illustrated in FIG. 5, the coupling factor K is heated by a beam path 17 due to the focusing arrangement 16.

The control arrangement of FIG. 4 may be applied in an analogous manner to the embodiment of FIG. 5 if, instead of the variation of the current, the light intensity or the duration of the light pulses such as, for example, the laser pulses, is controlled. 5

As hereinbefore mentioned, the method of the invention is particularly advantageous if it is important to increase the coupling without having to add material to the coupling element or coupler in the process. Furthermore, since the adjustment may be made on the completed filter, the result of the alignment may be directly followed in electronic curve tracers such as, for example, Oscilloscopes, thereby providing an alignment to a predetermined filter curve. Since relatively great variations are attainable in the coupling factor, the tolerances to be preset for the manufacture of the filter may be selected larger and the properties of the material used for the couplers or coupling elements may vary within wider limits. Although the variation or change of the Youngs modulus is accompanied by a variation of the temperature coefficient of the material of the coupling element, such variation, which is in the order of one part in a thousand, is practically insignificant with regard to the required accuracies.

The control device 12 of FIG. 4 may comprise any of a great number of suitable arrangements. In one suitable arrangement, for example, the control device 12 is basically a very simple control device which controls the flow of current and, thus, the temperature in the coupling wire, in a manner similar to a thermostat. The control device 12 may comprise, for example, a bridge circuit having four arms, a first of which has a fixed resistor, a second of which has a fixed resistor and a third of which has a variable resistor. The bridge is energized by a constant voltage applied to the junction point of the first and second arms and the junction point of the third and fourth arms. The fourth arm of the bridge has a pair of terminals connected to the temperature sensor 11, which may comprise, in the illustrated example, a heat-dependent resistor. The variable resistor of the third arm of the bridge may determine a desired temperature. A control voltage may be derived from 'the junction between the first and third arms of the bridge and the junction between the second and fourth arms of the bridge, and drives a motor, for example, for adjusting the current-controlled resistor 10. In a similar manner, the regulation of the current heat may be manually effected via the regulating device 9.

The light intensity or duration of the light pulses of the light source of FIG. 5 may be controlled in a similar manner.

While'the invention has been described by means of specific examples and in specific embodiments, I do not wish to be limited thereto, for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention.

1 claim:

1. A method for aligning a mechanical filter having individual filter resonators coupled to each other by coupling elements formed of material having a Youngs modulus dependent upon the temperature of a final heat treatment to which the material has been subjected, which comprises further heat treating the coupling elements to a maximum temperature which is higher than the final heat treatment temperature so as to change the Young's modulus of the material.

2. A method as claimed in claim 1, wherein the coupling elements are heat treated in a manner whereby the Youngs modulus is increased.

3. A method as claimed in claim 1, wherein the coupling elements are individually heat treated by direct current heating.

4. A method as claimed in claim 1, wherein the coupling elements are individually heat treated by radiations of a light source.

5. A method as claimed in claim 1, wherein the coupling elements are individually heat treated by radiations of a laser.

Claims

2. A method as claimed in claim 1, wherein the coupling elements are heat treated in a manner whereby the Young''s modulus is increased.
3. A method as claimed in claim 1, wherein the coupling elements are individually heat treated by direct current heating.
4. A method as claimed in claim 1, wherein the coupling elements are individually heat treated by radiations of a light source.
5. A method as claimed in claim 1, wherein the coupling elements are individually heat treated by radiations of a laser.