Abstract:
A moving mirror support device for use with photo-interferometers having first leaf springs arranged in parallel with one end thereof being fixed to a base; a coupling plate fixed to the other ends of the first leaf springs; and second leaf springs arranged in parallel with each of the first springs with one end thereof being fixed to the coupling plate and the other end being fixed to the moving mirror, whereby longitudinal and transverse displacements of the moving mirror can be more accurately controlled.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     This invention relates to a moving mirror support device for use in, for example, photo-interferometers, and more particularly, to an improvement therein for improving operation thereof. 
     2. Description of the Prior Art 
     In spectral analyzers or various measuring instruments using photo-interferometers, moving accuracy of the order of μm is required of the moving mirror support device. However, if such instruments are used at a plant site, there is the problem of inability to attain high accuracy of measurement due to various environmental influences, such as vibration. In order to solve this problem, in the prior art, the rigidity of a moving mirror support device in directions other than the moving direction thereof was enhanced by arranging a pair of leaf springs to be parallel to each other. 
     FIG. 1 shows a Michelson interferometer, which is commonly used as a spectrometer in a spectral analyzer, wherein a light beam from light source  1  is changed to a parallel light by collimating lens  2 , then divided into two directions with beam splitter  3 . Moving mirror  4  and fixed mirror  5  return each light beam back to beam splitter  3  in opposite directions, and the return light beams are superimposed on beam splitter  3 . The physical properties of the measured object (not shown) are measured by using the optical interference generated by the superimposed light beams. 
     FIG.  2 ( a ) shows a conventional support device for a moving mirror used in such an interferometer, wherein moving mirror  4  is suspended from an upper position by two leaf springs  11  mounted on base  10  parallel to each other. Suspension by two leaf springs can suppress rotational motion generated when the moving mirror  4  is operated. If such an interferometer is used in a spectral analyzer, the moving mirror is driven transversely by a voice coil motor (not shown) about 0.3 mm and at 8 Hz. In such case, it is necessary to increase the amplitude (i.e. movement in the transverse direction) of the moving mirror in order to improve the resolution of the analyzer. However, by increasing the amplitude of the moving mirror  4 , deformation of the two leaf springs  11  becomes large, as shown in FIG.  2 ( b ), and the moving mirror is displaced transversely and longitudinally. Thus, the problem of longitudinal displacement arises and the optical axis of the return light will be shifted. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the invention is to solve the foregoing and other problems, disadvantages and deficiencies of the prior art. 
     Another object is to provide a moving mirror support device, such as used in photo-interferometers, that has no longitudinal displacement when the transverse amplitude is increased. 
     The foregoing and other objects are attained by the invention which encompasses a moving mirror support device that has a plurality of first leaf springs arranged in parallel and held at a predetermined distance, one end of each leaf spring being fixed to a base; a coupling plate fixed to other ends of the first leaf springs; and a plurality of second leaf springs, each being arranged in parallel with each of the first leaf springs, one end of each being fixed to the coupling plate and the other end being fixed to the moving mirror. 
     Advantageously, the invention device eliminates displacement of the moving mirror in the longitudinal direction even when the transverse direction amplitude is increased. 
     In another embodiment, a damper is further provided to regulate the movement of the coupling plate, thereby enabling increased stability of the moving mirror. 
     In a further embodiment, control devices are added which control vibrations of the coupling plate based on signals from a position detecting device that senses displacement of the coupling plate and/or moving mirror. These added features further increase the stability of the moving mirror. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a drawing depicting an example of a conventional interferometer used for spectral analysis. 
     FIG. 2 is a side view depicting a conventional moving mirror support device used for photo-interferometers. 
     FIG. 3 is a side view depicting a first illustrative embodiment of the invention. 
     FIG. 4 is a drawing useful for explaining movement of the leaf springs of the embodiment of FIG.  3 . 
     FIG. 5 is a side view depicting a second illustrative embodiment of the invention. 
     FIG. 6 is a side view depicting a third illustrative embodiment of the invention. 
     FIG. 7 is a side view depicting a fourth illustrative embodiment of the invention. 
     FIG. 8 is a side view depicting a fifth illustrative embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiment depicted in FIG.  3 ( a ) comprises four leaf springs  11   a  and  11   b  that have the same shape and nearly the same elastic modulus. One end of each of the outer two first leaf springs  11   a  is fixed to base  10  vertically and the other end thereof is fixed to each end of coupling plate  12 , respectively, thereby to support coupling plate  12  horizontally. One end of each of the two inner second leaf springs  11   b  is fixed to coupling plate  12 , and moving mirror  4  is fixed to the other end of each of leaf springs  11   b  thereby supporting or suspending moving mirror  4 . Each of both leaf springs  11   a  and  11   b  (i.e. each pair) is formed in parallel with each other and held at a predetermined distance so that all of the leaf springs have an effective length L. 
     FIG.  3 ( b ) shows the state in which a force of large amplitude, for example, amplitude of about 3 mm at 2 Hz, is applied to moving mirror  4  in a transverse direction (see arrow X), such as by use of a voice coil motor (not shown). In this case, the outer first leaf springs  11   a  and the inner second springs  11   b  are bent in the longitudinal direction by early equal amounts so that movement of the moving mirror  4  upward or downward does not occur. That is, moving mirror  4  is moved linearly (i.e. in the direction of arrow X) and interference light is obtained accurately and reliably without shifting the optical axis of the return light. 
     FIG. 4 is useful in explaining the movement of the leaf springs of the support device of FIGS.  3 ( a ) and  3 ( b ). When moving mirror  4  is moved , for example in the direction of the dotted lines, the moving distance d 2  of moving mirror  4  becomes twice that of the moving distance of the coupling plate  12 , (i.e. dl×2). However, the ratio of these movements is not always maintained accurately due to vibration of the leaf springs and highly accurate amplitudes (i.e. transverse motion of the moving mirror  4 ) cannot always be maintained. As a result, although the foregoing first embodiment is a substantial improvement over the prior art when considered by itself, further improvements are made by other embodiments of the invention, as will be discussed hereinbelow. 
     FIG. 5 shows a support device which further improves the first illustrative embodiment, wherein a damper  13  is provided to regulate the motion or movement of the coupling plate  12  to suppress vibrations the leaf springs  11   a  and  11   b . Damper  13  is connected to the side of coupling plate  12  as depicted. The ratio of displacements of coupling plate  12  and moving mirror  4  is shifted due to the presence of damper  13 , and upward and downward displacements are generated in moving mirror  4 . However, in the device, contact is achieved using a suitable force such that the displacement does not affect the accuracy of the supporting device for the moving mirror. As discussed, vibration, generated when moving mirror  4  is driven, can be suppressed by use of the damper  13  contacting the coupling plate  12  thereby to control motion thereof. 
     FIG. 6 shows a third illustrative embodiment wherein a position detecting device  15  is mounted on the side of coupling plate  12 , and the vibration of leaf springs  11   a  and  11   b , generated when moving mirror  5  is driven (such as by a driving means, not shown), is suppressed by a control device  16   a , which operates to control the vibration of the leaf springs  11   a  and  11   b , based on signals from the position detecting device  15   a . Control signals are sent from the control device  16   a  to the actuator or voice coil motor  17  thereby to effect control supression of coupling plate  12  so that movement thereof becomes one half (½) of the movement of the moving mirror  4 . 
     FIG. 7 shows a fourth illustrative embodiment, wherein a position detecting device  15   b  is provided to monitor the displacement of the moving mirror  4 . Moving mirror  4  is driven by moving mirror control device  16   b  based on signals obtained from the position detecting device  15   b  with control signals being sent to a first actuator  17  (also labelled voice coil motor). Another control device  16   c  is used to control suppression of movement of the coupling plate  12  based on signals from the position detecting device  15   b  via control device  16   b , as shown. The suppression is accomplished by the second actuator  17  (also called voice coil motor), in the same manner as in FIG.  6 . This embodiment provides stable operation as in the the embodiment of FIG.  6 . 
     FIG. 8 shows a fifth illustrative embodiment , wherein a plate position detecting device  15   a  and a mirror position detecting device  15   b  are connected to the control device  16 . Responsive to signals from one or both of the position detecting devices  15   a  and  15   b , the control device  16   d  provides control signals to the actuator or voice coil motor  17  thereby to suppress motion of the coupling plate  12 . It is noted that there is no actuator  17  or voice coil motor shown to move the mirror  4 . However, as in all of the other embodiments, it is to be understood that such means for moving the mirror  4  is provided to control such moving mirror  4 . 
     In all of the embodiments, the devices  17  accurately control the amplitude ratios of the movement of the coupling plate  12  and the movement of the moving mirror so as to more accurately control the linear displacement. In the embodiment of FIG. 8, the displacement of the coupling plate  12  is in a predetermined ratio of 1:2 with respect to the moving mirror. This is accomplished, as in the other embodiments by the control device receiving signals from the position detectors which measure the displacements of the coupling plate and/or moving mirror and in response thereby control the movement or suppression of movement of the coupling plate and/or moving mirror. 
     The foregoing description is merely illustrative of the principles of the invention. Various extensions and modifications thereof would be apparent to the worker skilled in the art. It is understood that all such extensions and modifications are to be considered to be within the spirit and scope of the invention. 
     For example, the moving distance and moving periodicity (Hz) or mounting positions of the components can be changed as desired. It is sufficient that upward and/or downward displacement not be caused due to transverse amplitudes. Moreover, the invention is not limited to use in spectral analyzers. For example, the invention can be used in wavelength measuring devices, OTDR devices, etc. 
     As described above and in the claims, mounting two sets of pairs of leaf springs allows the moving mirror to perform linear motion even when its moving distance is lengthened and resolution of spectral analyzers is improved. Moreover, as described above and in the claims, providing. a damper to contact the coupling plate suppresses vibrations of the leaf springs which are generated when driving the moving mirror. This provides greatly increased stability of operation. Finally, as described above and in the claims, monitoring the displacement of the coupling plate and/or moving mirror and controlling the vibrations thereof selectively using a control device also suppresses vibration of the leaf springs generated when driving the moving mirror, provides increased stability of operation.