Optical apparatus provided with a driving unit for moving a lens

Abstract: This specification discloses an optical apparatus provided with a lens unit movable in the direction of the optical axis thereof, a lens barrel, an electromagnetic coil coupled to one of the lens unit and the lens barrel, a driving unit having a magnetic material coupled to the other of the lens unit and the lens barrel, and a guide for slidably guiding the lens unit relative to the lens barrel.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a photo-taking system of a camera for silver salt film, a still video camera, a video camera or the like; and particularly to an optical apparatus provided with a driving unit for moving a lens unit for zooming or focusing or both in a portion of a lens barrel. Related Background Art It has heretofore been usual with the lens driving mechanism of a camera or the like to transmit the drive force of a motor by a driving mechanism such as a feed screw or a cam cylinder and a belt and a gear with the aid of a DC motor or a stepping motor to thereby move a focusing lens or a lens for zooming. However, such example of the prior art has suffered from problems which will hereinafter be described. Torque created by a DC motor or a stepping motor is generally a drive force in the direction of rotation, and to rectilinearly move a lens in the direction of the optic axis, members such as a feed screw and a cam have become separately necessary and it has been difficult to make a lens barrel compact. Also, vibration and noise have been produced from the motor unit and the gear unit and torque efficiency has been low, and this has given rise to a problem that much electric power is consumed. On the other hand, the applicant has proposed in Japanese Laid-Open Patent Application No. 58-16208 a mechanism for rotating a lens holding cylinder helicoid-coupled to a body by electromagnetic induction between a lens holding cylinder and an outer cylinder thereof to thereby move a lens unit back and forth, but loss of energy occurs in the helicoid-coupled portion and the movement still exists and the driving operation is performed in indirect manner. Document JP-A-57-108806 discloses an automatic focus control device wherein the position of a lens is controlled automatically. In this device a permanent magnet is added to a mobile part to fix the lens and an electromagnetic coil is added to a part to support the mobile part. The permanent magnet, being constituted by a ring-shaped permanent magnet, is fixed to the outer circumference of a lens frame at the mobile part where the lens is fixed, while the electromagnetic coil is fixed opposite to the permanent magnet to the inside of a sleeve. The permanent magnet and the electromagnetic coil consist of four parts, respectively, in order to provide a motor consisting of the permanent magnet and the electromagnetic coil serving as stator and rotor, respectively. As a reaction to a current provided in the electromagnetic coil a rotation of the permanent magnet and the electromagnetic coil relative to each other around the common optical axis of the lens frame and the sleeve is performed. This rotational movement is transformed into a lens movement in the x-y direction (optical axis direction). Furthermore, from document US-A-4 534 624 an apparatus is known, comprising a lens barrel operated by electromagnetic induction wherein the lens barrel consists of a front, middle and rear lens barrel, and e.g. the middle lens barrel serves as a stator. A movable element is formed in a hollow space. Furthermore, in this apparatus front, variator, compensator and focusing lens groups are provided, the front lens group being fixed in the front lens barrel. Moreover, a permanent magnet and ferromagnetic members each comprising a plurality of teeth are provided. The plurality of ferromagnetic members are part of a plurality of electromagnetic coils. These electromagnetic coils can be provided in a ring-shaped manner around the inside surface of the lens barrel. In case of this arrangement a current supplied to at least one of the plurality of electromagnetic coils results in a rotational movement of the lens barrel and the lens unit relative to each other, said rotational movement being transformed in a linear movement of the lens unit along the optical axis. Furthermore, it is possible to arrange a plurality of electromagnetic coils at the inside of the lens barrel in a direction parallel to the optical axis, the "teeth" of the permanent magnet being arranged opposite to the plurality of poles of the electromagnetic coils. A linear movement of the lens unit is accomplished by means of a complex current control of the current supplied to the different electromagnetic coils. Moreover, document JP-A-63-163312 discloses an automatic focusing device and its lens driving mechanism which moves and controls a focusing lens directly in the direction of its optical axis. The lens driving mechanism comprises a driving means for a linear motor. The focusing lens is supported by a magnet between solenoids. Furthermore, resilient members are provided for positioning the focusing lens. Document EP-A-0 458 694, which constitutes prior art within the meaning of Article 54(3) EPC, discloses a lens barrel comprising a lens unit movable with respect to an outer shell by electromagnetic induction, the lens barrel further comprising detection means for detecting the position and the speed of the lens unit. SUMMARY OF THE INVENTION It is an object of the present invention to provide a driving device which effects more direct lens driving and suppresses the wasteful consumption of electric power and can be incorporated into a small space, and it is a second object of the present invention to provide an optical apparatus incorporating the driving device therein. It is another object of the present invention to provide an optical system incorporating therein a device capable of accurately measuring the position or the amount of movement of a lens. According to the present invention this object is accomplished by an apparatus comprising: a lens barrel; a lens unit arranged within said lens barrel and movable in the direction of its optical axis with respect to said lens barrel; a guiding mechanism comprising a resilient member for guiding said lens unit such that said lens unit can be moved in its optical axis direction; and an electromagnetic induction coil and a magnetic member constituting a driving means for driving said lens unit with respect to the lens barrel by electromagnetic induction, said electromagnetic induction coil being coupled to one of the lens unit and the lens barrel, and said magnetic member being coupled to the other of the lens unit and the lens barrel; said apparatus being characterized in that detecting means are provided for detecting the relative position or the relative motion between said lens unit and said lens barrel, said detecting means being arranged to carry out said detection by detecting strain of said resilient member. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a vertical cross-sectional view showing a first explanatory example. Figure 2 is a front view of the first explanatory example. Figure 3 shows a second explanatory example in which the first explanatory example is applied to an optical system. Figure 4 is a vertical cross-sectional view of a third explanatory example. Figure 5 is a vertical cross-sectional view of a fourth explanatory example. Figure 6 is a vertical cross-sectional view of a fifth explanatory example. Figure 7 is a transverse cross-sectional view of a sixth explanatory example. Figure 8 is a vertical cross-sectional view of the sixth explanatory example. Figure 9A is a vertical cross-sectional view of a seventh explanatory example. Figure 9B is a cross-sectional view taken along line X-Y-X' of Figure 9A. Figure 10 is an illustration of constituent members. Figure 11A is a vertical cross-sectional view of an eighth explanatory example. Figure 11B is a cross-sectional view taken along line X-Y-X' of Figure 11A. Figure 12 is a vertical cross-sectional view of a first embodiment of the present invention. Figure 13 is a front view of the first embodiment. Figure 14 illustrates the action of a gimbal spring. Figures 15A and 15B illustrate the axial deformation of the gimbal spring. Figure 16 is a front view of a modification of the gimbal spring. Figure 17 is a vertical cross-sectional view of a second embodiment of the present invention. Figure 18 shows the assembly of a mechanical system and an electrical system according to a third embodiment of the present invention. Figure 19 is a front view of the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Figure 1 shows a cross-sectional view of an explanatory example, and Figure 2 shows a view thereof as it is seen in the direction of the optical axis x. Figure 3 shows an example of a zoom lens which cqmprises a positive forward lens unit A, a negative variator B, a fixed lens unit C and a positive movable lens unit 1 for compensation and focusing. This zoom lens can be applied to lenses of other various zoom types, and can also be applied to the focusing lens portion of a single-focus lens. In the following description, the application of a driving actuator DA1 to the lens unit 1 is adopted by way of example, but if as shown in Figure 3, a driving actuator DA2 is also provided in the variator B and movement is effected at the same time, zooming will become possible. It is to be understood that each of the lens units A, B and C comprises one or more single lenses. In Figures 1 and 2, the reference numeral 1 designates a lens unit comprising elements 1a, 1b and 1c. The reference numeral 2 denotes a lens holding cylinder for holding the lens unit 1. The reference numeral 3 designates a coil, and the reference numeral 4 denotes an annular bobbin. The coil 3 is wound on the bobbin 4 to thereby constitute an electromagnetic coil, and as shown in Figure 2, the lens holding cylinder 2 and the bobbin 4 are coupled together in an area wherein an inner yoke 6 is absent, by an arm 2a for coupling. On the other hand, the reference numeral 5 designates an outer yoke, and the reference numeral 6 denotes an inner yoke. These yokes extend in the direction of the optical axis from a permanent magnet 7. The outer yoke 5 and the permanent magnet 7 are coupled to a lens barrel 8. In that case, the bobbin 4 forms an annular band about the optical axis, and the inner yoke 6, the outer yoke 5 and accordingly the permanent magnet 7 form portions of the annular band. In the present explanatory example, the inner side of the bobbin 4 and the outer peripheral surface of the inner yoke 6 are polished, and these two contact with each other to constitute a plain bearing. Also, a magnetic circuit is formed by the outer yoke 5, the inner yoke 6 and the permanent magnet 7. In the present apparatus, the lens unit 1, the coil 3 and the yokes 5,6 are coaxially disposed as described above. The operation of the present apparatus will now be described. The electromagnetic coil comprising the coil 3 and the bobbin 4 is placed in a magnetic flux produced by the magnet 7, and an electric current is caused to flow from an electric wire, not shown, to the coil 3 in a selected direction, whereby the coil 3, the lens unit 1 and the lens holding cylinder 2 receive a driving force in the direction of the optical axis. At this time, the yokes 5,6 which are disposed outside and inside form a closed magnetic circuit and the leakage flux is small and, therefore, a relatively great driving force is produced by small electric power. Also, since the lens unit 1, the coil 3 and the yokes 5,6 are coaxially disposed, the driving force is uniformly applied to the cross-sections of the coil 3 and the bobbin 4. Further, the apparatus is of such structure that the movement of the lens unit 1 is guided by the sliding surface between the bobbin 4 and the inner yoke 6, and in this straight guide mechanism as well, the elements are coaxially disposed and therefore, sliding friction also occurs uniformly in the cross-section of the coil 3. Thus, both the driving force and the sliding friction are produced axis-symmetrically with respect to the optical axis and, therefore, there is created no force which inclines the lens surface. Therefore, the lens unit 1 is movable smoothly and at a high speed in the direction of the optical axis. Further, the lens holding cylinder 2 and the constituents for driving force production and straight guide are made integral with each other, whereby the compactness and light weight of the lens barrel 8 is realized. In the explanatory example of Figure 1, in supplying electric power to the coil 3, the electromagnetic coil 3,4 is of such structura that it slides between the edges of the arm 2a of the lens holding cylinder 2 and the inner yoke 6 in order to prevent the electromagnetic coil 3,4 from rotating about the optical axis. If a material of small coefficient of friction, for example, fluorine resin, is employed for the bobbin 4 of the present apparatus, the bobbin 4 will become easier to move. Alternatively, a metal of strong magnetism may be used to increase torque. In this case, the use of a sintered metal of low coefficient of friction impregnated with a lubricant would also be effective. In the structure shown in Figure 4, a sheet-like lubricating member 21 is provided on the surface of contact between the bobbin 4 and the inner yoke 6 to mitigate the above-described friction. Figures 4 and so on depict the upper half above the optical axis x, and the lower half also is of symmetrical structure. The same members as those previously described are given the same reference numerals. An example of the case where ball bearings are discretely employed to decrease frictional resistance is shown in Figure 5. In Figure 5, the reference numerals 22 and 22' designate ball bearings disposed between the bobbin 4 and the inner yoke 6. One or both of the opposed surfaces of the bobbin 4 and the inner yoke are formed with grooves in the direction of the optical axis X to prevent the coil 3 from rotating in the circumferential direction and at the same time, prevent the balls of the ball bearings 22,22' from leaning toward a portion. Figure 6 shows an example of a lens driving apparatus for guiding movement by the outer peripheral surface of the bobbin 4. The apparatus of this figure is comprised of members similar to those in Figure 1, with the exception of the absence of the yokes 5 and 6. The direction of turn of the coil 3 is similar to that in the first explanatory example, and an elongated permanent magnet 7 is disposed so that its polarities may split in the direction of the optical axis X as shown. In this apparatus, when the coil 3 is electrically energized through a direction selecting switch, not shown, the magnetic field of the permanent magnet 7 and the magnetic field of the coil 3 act to produce a force which moves the coil 3 in the direction of the optical axis. Also, the outer peripheral portion of the bobbin 4 contacts with the inner peripheral surface of the magnet 7 to thereby effect the rectilinear guide of the lens movement. The constructions of Figures 4 and 5 can also be adopted to decrease the friction of the surface of contact. In the construction of the present explanatory example, a magnetic force is also produced in the radial direction, but since the lens unit 1, the coil 3 and the magnet 7 are coaxially disposed, forces are balanced axis-symmetrically and it is difficult for a force which will incline the lens surface to be created. In the construction of the present apparatus, the permanent magnet 7 is not a closed magnetic circuit and therefore, the magnetic flux passing through the coil 3 becomes small and torque efficiency is bad as compared with the above-described explanatory example, but there are the following effects. Since the bobbin 4 and the lens holding member 2 are formed integrally with each other and the arm portion 2a need not be provided, it is easy to make these by integral molding. Also, the diameters of the bobbin 4, the coil 3 and the yokes 5,6 can be made smaller correspondingly to the absence of the arm portion 2a, and this leads to the effect that the lens barrel 8 generally becomes compact. Figure 7 shows another explanatory example, and Figure 8 depicts the plane A-x-A' of Figure 7 as it is developed. The present apparatus is characterized in that it has bars 23, 23' and the sleeve portion 2b of the holding cylinder 2 as a straight guide mechanism for the lens unit 1. This is particularly effective in a case where as in a video camera of high image quality, the eccentricity of the optical axis of the lens unit 1 is suppressed highly accurately. The bars 23 and 23' are fixed to the outer cylinder 8 in a direction parallel to the optical axis X and mounted on a support member 52. The sleeve portion 2b can slide on these bars 23 and 23' and therefore, the lens unit 1 and the holding cylinder 2 and a member connected thereto are guided in the direction of the optical axis X. The principle of the driving force generation of the present apparatus is similar to that in the first explanatory example, that is, by causing an electric current to flow to the electromagnetic coil 3, the holding cylinder 2 holding the lens unit 1 receives a load in the direction of the optical axis X. As previously described, these members are rectilinearly guided and can therefore be moved stably and smoothly in the direction of the optical axis X. In the present apparatus, the sleeve is made common to a portion of the lens holding cylinder 2, whereby the number of parts is decreased and the lens barrel 8 is made compact. Description will now be made of an explanatory example in which the amount of movement or the stopped position of the moved lens unit can be detected. The detection is done to accurately know the position of the lens unit moved for zooming, or to confirm the amount of movement of the lens unit be moved for focusing. Figure 9A shows the vertical cross-section of a portion of the photo-taking lens, and Figure 9B depicts the cross-section taken along the line X-Y-X' of Figure 9A. The lens driving unit comprises a fixed portion 42 of a hollow cylindrical shape fixed to a lens barrel 41, and a movable portion 43 slidable relative to the fixed portion 42. The fixed portion 42 has bobbins 44, 45, coils 46, 47 and a stator yoke 48. The bobbins 44 and 45 are provided on the opposite sides of the central pole of the stator yoke 48, and the coils 46 and 47 are wound along the peripheral surfaces of the bobbins 44 and 45, respectively, and a voltage may be applied thereto from terminals 49 and 50. The movable portion 43 has a lens 31 with a magnetized optical system holding member 51 disposed inside thereof. The magnetized optical system holding member 51 is, for example, a plastic magnet, and only a portion of the optical system holding member 51 may be magnetized. Alternatively, an iron piece may be adhesively secured to the outer peripheral surface of the optical system holding member 51 and the surface thereof may be Teflon-worked to make it readily slidable. The lens 31 is held by the optical system holding member 51. The fixed portion 42 and the movable portion 43 need not always be provided over the entire circumference. The principle of operation of the lens driving unit of the present explanatory example is similar to the principle of operation of an iron core type motor. The magnet 51 always produces constant magnetic fluxes B M1 and B M2 , and constitutes a magnetic circuit so as to surround the coils 46 and 47. When a DC voltage is applied to the terminals 49 and 50, an electric current flows to the coils 46 and 47, and a magnetic flux B C is produced by the coils 46 and 47. By changing the direction of the electric current, the direction of the magnetic flux B C can be changed. The magnetic fluxes B M1 and B M2 and the magnetic flux B C weaken or strengthen each other to thereby produce a thrust in one direction, and by this thrust, the movable portion 43, i.e., the lens 31, is slidden along the optical axis. One position detector is a magnetic encoder, and as shown in Figure 10, a projected pole portion 51b is provided at one end of the optical system holding member 51, and a magnetic recording portion 51b multipole-magnetized in the direction of the optical axis is on the sliding surface of the projected pole portion 51b, and a magnetic sensor 54 is provided in the stator yoke 48 in opposed relationship with the magnetic recording portion 51b through a distance at which can be detected the leakage magnetic field from the magnetic recording portion 51b resulting from the sliding movement of the movable portion 43 in the direction of the optical axis. From the necessity of detecting a weak leakage magnetic field from the magnetic recording portion 51b, the magnetic sensor 54 is provided in the stator yoke 48 in such a manner as to be surrounded through a non-magnetic member 53 to prevent the influence of the leakage magnetic fields of the magnet 51a and coils 46, 47 of the lens driving unit. As previously described, the optical system holding member 51 serves as the optical system holding frame, the magnet of the lens driving apparatus and the magnetic recording portion of the posiiton detector, whereby the lens barrel 41 can be made compact and light in weight as well as low in cost. Also, the movable portion 43 can be made long in the direction of the optical axis to thereby suppress the eccentricity thereof in the direction of the optical axis and, thus, there can be provided a stable structure in which the fluctuation of the distance between the magnetic recording portion 51b and the magnetic sensor 54 is small. Thereby, there can be obtained a stable position detection signal of high accuracy. A further explanatory example will now be described with reference to Figures 11A and 11B. This explanatory example differs from the previous explanatory example in that coils 67 and 68 are provided on a movable portion 63 and that a fixed portion 62 is formed of a magnetic material. That is, the lens driving unit comprises a fixed portion 62 of hollow cylindrical shape fixed to a lens barrel 61 and a movable portion 63 slidable relative to the fixed portion 62. The fixed portion 62 is formed of an iron piece, and the inner peripheral surface thereof is, for example, Teflon-worked to thereby make the movable portion 63 readily slidable. The movable portion 63 has bobbins 65, 66, coils 67, 68 and a yoke 64. The bobbins 65 and 66 are provided on the opposite sides of the central pole of the yoke 64, and the coils 67 and 68 are wound along the peripheral surfaces of the bobbins 65 and 66, respectively. The coils 67 and 68 are series-connected, and a voltage may be applied thereto from terminals 69 and 70. The yoke 64 is, for example, a plastic magnet, and serves also as an optical system holding member. The yoke 64 is entirely or partly magnetized, and constitutes a magnetic circuit so as to surround the coils 67 and 68. For example, the yoke 64 may be magnetized so that the central pole may be a north pole, the opposite end poles may be south poles, the diametrically outer peripheral side with respect to the central pole may be a north pole and the inner peripheral side may be a south pole. The principle of operation of the present explanatory example is similar to that of the previous explanatory example, that is, similar to the principle of operation of an iron core type motor. One position detector is a magnetic encoder, and a projected pole portion 64b is provided at one end of the yoke 64, and a magnetic recording portion multipole-magnetized in the direction of the optical axis is on the sliding surface of the projected pole portion 64b, and a magnetic sensor 72 is provided on the fixed portion 62 in opposed relationship with the magnetic recording portion through a distance at which can be detected the leakage magnetic field from the magnetic recording portion resulting from the sliding movement of the movable portion 63 in the direction of the optical axis. From the necessity of detecting a weak leakage magnetic field from the magnetic recording portion, the magnetic sensor 72 is provided on the fixed portion 62 in such a manner as to be surrounded through a non-magnetic member 73 to prevent the influences of the leakage magnetic fields of the magnet 64a and coils 67, 68 of the lens driving unit. As previously described, the yoke 64 serves as the optical system holding frame, the magnet of the lens driving apparatus and the magnetic recording portion of the position detector and thus, the compactness, light weight and low cost of the lens barrel 61 can be achieved. Also, the movable portion 63 can be made long in the direction of the optical axis to thereby suppress the eccentricity in the direction of the optical axis and thus, there can be provided a stable structure in which the fluctuation of the distance between the magnetic recording portion 64b and the magnetic sensor 72 is small. Thereby, there can be obtained a stable position detection signal of high accuracy. While the above-described explanatory examples are of a construction in which the movable lens unit is guided in the direction of the optical axis by a guide member having a sliding surface, the following first embodiment of the present invention is such that the movable lens unit 1 is supported by a resilient plate. The construction in which the movable lens unit 1 is supported by a resilient plate is effective to decrease friction, but is not Very suitable for great movement and therefore, is effective when it is used for the compensation and focusing of a zoom lens. Referring to Figures 12 and 13, it is readily understood that a lens holding frame 83 is disposed in the outer cylinder 87 of a lens barrel and lenses 84a and 84b are fixed to the holding frame 83. The lens holding frame 83 is supported in the outer cylinder 87 of the lens barrel by two resilient flat plates, for example, gimbal springs 81 and 82. The resilient flat plates 81 and 82, as shown in Figure 13, have concentric cut-out portions 90 indicated by hatching. Accordingly, where a single resilient flat plate is used as shown in Figure 14, the holding frame 83 moves freely in directions z,  and ψ shown. However, it is held in directions x and y with a relatively strong force. So, if two resilient flat plates 81,82 are disposed parallel to each other as shown in Figure 15A and the lens holding frame 83 is fixed thereto, the holding frame 83 will become unmovable or unrotatable in the directions x, y,  and ψ and movable only in the direction z. Figure 15A shows a case where the resilient flat plates 81 and 82 are balanced, and Figure 15B shows a state in which the holding frame 83 has been moved in the direction z. A permanent magnet 89 far driving the lens holding frame 83 in the direction of the optical axis is fixed to or embedded in the outer peripheral portion of the holding frame 83, or it is magnetized. Also, an electromagnet comprising an iron core 85 and a coil 86 wound thereon is disposed correspondingly to the permanent magnet 89. The resilient flat plates 81 and 82 are formed, for example, from phosphor bronze or stainless steel plate by etching, or are inexpensively made of plastic molded articles, and a strain gauge 88 which is movement distance detecting means is attached to a portion thereof. The present embodiment is constructed as described above and therefore, when the coil 86 is electrically energized, a magnetic field is produced around the iron core 85, and by varying that electrically energized state, i.e., the polarity of the electromagnet 85,86, there are produced attraction and a repulsive force between the electromagnet 85,86 and the permanent magnet 89. Therefore, the holding frame 83 to which the permanent magnet 89 is fixed obtains a driving force relative to the outer cylinder 87 and moves in the direction of the optical axis. Accordingly, the lenses 84a and 84b are moved in the direction of the optical axis and focusing or the adjustment of the focal lengths of these lenses can be accomplished. Also, the strain gauge 88 is attached to each resilient flat plate 81,82 and therefore, when the holding frame 83 moves in the direction of the optical axis, the amount of deformation of the resilient flat plate 81 can be directly detected, and it is possible to convert this detected value to thereby detect the amount of movement of the lens unit in the direction of the optical axis. Figure 16 shows another embodiment of the resilient flat plate. According to this embodiment, cut-out portions 100 indicated by hatching are formed in an eddy-like shape, that is, are cut out in such a manner that the diameter thereof becomes progressively larger. The resilient flat plate 91 of the present embodiment is also used in the same manner as the flat plate shown in Fig. 12 and has a similar effect, but according to the present embodiment, an arm portion 91a subjected to deformation is longer than that of Figure 13 and therefore, the lens unit can be moved with a light driving force and thus, less electric power is required of the actuator. Figure 17 shows an embodiment in which a single resilient flat plate 91 is used. That is, a lens holding frame 93 is supported at one end thereof by the resiiient flat plate 91 and the outer periphery 93a of the other end portion thereof is axially movably supported by a plurality of guide rollers 101 and 102. According to the present embodiment, the movements of the lens holding frame 93 in the aforementioned directions  and ψ are restricted by the guide rollers 101 and 102 and, therefore, as in the embodiment using two resilient flat plates, the holding frame 93 is movable only in the direction of the optical axis. The other constituents are given the same reference characters and need not be described. Although not shown, it is apparent that the guide rollers 101, 102 can be replaced by guide pins, bar sleeves or the like. In the embodiments shown in Figures 12 and 13, a strain gauge 88 is used to detect the position or the amount of movement. The strain gauge 88 is known as what measures strain by utilizing the nature that the resistance value of a semiconductor varies when strain is exerted on the semiconductor. In a compact rear focus type zoom lens, the lens positioning accuracy required is high and for example, with the 8-time zoom for 113' CCD image pickup element, it is sometimes the case that even a detection resolving power of the order of several microns is required. Also, in the auto focusing of the type in which in-focus state is judged from an image signal, a mechanism for vibrating a portion of the lens unit at a high speed in the direction of the optical axis (wobbling) is required and therefore, high detection responsiveness is desired. The following embodiment provides a construction in which highly accurate detection is possible. Figure 18 shows a construction in which the lens holding cylinder of the explanatory example of Figure 1 is supported by the gimbal springs shown in Figures 14 and 15, instead of slidable bearings. The reference numeral 100 designates a lens unit, and the reference characters 100a, 100b and 100c denote component lenses. The reference numeral 102 designates a holding cylinder, and the reference numeral 105 denotes an outer lens barrel. The reference numerals 131 and 132 designate gimbal springs which, as shown in the front view of Figure 19, are formed by punching a spring plate except for hatched portions, and the characteristic of the gimbal mechanism is such that the freedom of movement in forward and backward directions is given. The holding cylinder 102 has its force and rear portions supported on the lens barrel 105 by the gimbal springs 131 and 132. The reference characters 133a and 133b denote permanent magnets, each of which is formed by cutting out an annular shape by about a quarter of a circle and gluing a north pole and a south pole thereto, and the reference characters 134a, 134b and 135a, 135b designate inner and outer yokes, respectively. The reference numeral 137 denotes an annular bobbin, and the reference numeral 136 designates an electromagnetic coil. On the other hand, the reference numerals 141 to 144 and 145 to 148 denote strain gauges. The present embodiment is of such structure that the lens unit 100 is directly moved by electromagnetic induction, and the voice coil type linear actuator of a closed magnetic system is constituted by the yokes 134a, 134b, 135a, 135b, the permanent magnets 133a, 133b and the coil 136. The electromagnetic coil 136 is wound on the bobbin 137, which is coupled to the lens holding cylinder 102. As mentioned above, the inner band of a part of each of the gimbal springs 131 and 132 is coupled to the lens holding cylinder 102, and the outer edge thereof is joined to the lens barrel 105. Accordingly, by a combination of the gimbal springs 131, 132 and the holding cylinder 102, the lens unit 100 can be rectilinearly guided only in the direction of the optical axis. Also, when an electric current is supplied to the coil 136, the lens unit 100 receives a driving force in the direction of the optical axis. The structure as shown eliminates any space for sliding and the adverse effect of friction can be avoided and thus, highly efficient and rapid driving becomes possible. On the other hand, in the present embodiment, the amounts of deformation of the gimbal springs are measured with the strain gauges 141 to 148 adhesively secured to four locations on orthogonal lines with the gimbal springs interposed between each pair of strain gauges on the front and back. The reason why the strain gauges 141 to 148 are disposed at four locations is that consideration is given to a case where the deformation of the gimbal springs 131, 132 is not rotation-symmetrical, and basically, they may be disposed at one location or at each one location on orthogonal lines. However, to accomplish precise position detection, it is desirable to take the average of four sets, but the circuit is shown with respect to one set as an example. In the signal processing system, the reference numerals 120 and 121 designate detection amplifiers connected to the strain gauges 145 and 146, respectively. The reference numerals 122 and 124 denote differential type amplifier circuits. The differential type amplifier circuit 122 is connected to the detection amplifiers 120 and 121. The reference numeral 123 designates a linearity correction circuit, the reference numeral 125 denotes a control circuit, and the reference numeral 126 designates a power amplifier circuit. Basically, the strain gauges may be provided only on one side. However, a method of using a pair of strain gauges to offset the influence imparted to resistance value by a temperature change is adopted as a method for eliminating such influence, but this method is not restrictive. Also, in some cases, the gimbal springs 131,132 are deformed by vibration to which the entire lens barrel 105 has been subjected, whereby the resistance values of the strain gauges are varied. Accordingly, depending on the required performance, such a countermeasure may become necessary. So, in the present embodiment, the strain gauges 141 to 148 are disposed with the springs 131, 132 interposed therebetween, and the fact that the influence of the strain gauges 141 to 148 and springs 131,132 is symmetrical is utilized to detect the difference between outputs by the differential amplifier circuit 122, thereby eliminating the influences of temperature changes and the vibration of the entire lens barrel 105. The output of the differential amplifier circuit 122 is converted into a signal indicative of the lens position by the linearity correction circuit 123 and the signal is output. By the above-described operation, the position of the lens unit 100 on the optical axis has been found as an electrical signal. Generally, the strain gauge is high in resolving power and also high in reproducibility because the element itself does not produce noise. Accordingly, the position detection resolving power obtained by the present apparatus is of the order of 10 -4 - 10 -5 mm, and this is a sufficient characteristic for the lens positioning of a camera. Further, the element itself has no factor which will cause sliding or back-lash and therefore, is quick in detection response and does not affect the driving condition. By using the circuits 124, 125 and 126 of Figure 18, a lens driving system is formed in a closed loop, and it is also possible to construct a system which can rapidly accomplish positioning in response to a desired command value. Therefore, rapid wobbling or the like for auto focusing which uses, for example, the output of a solid state image pickup element is also possible. Strain gauges of the semiconductor type have been taken as an example, but strain gauges utilizing piezo-electric elements may also be used. Also, as shown in Figure 19, two or more sets of strain gauges may be provided and set so as to cancel vibrations in multiple directions. The strain gauges themselves may also be manufactured integrally with resilient springs as by etching.

Claims: An apparatus comprising: a lens barrel (87; 97; 105); a lens unit (84a, 84b; 94a, 94b; 100, 100a - 100c) arranged within said lens barrel (87; 97; 105); a guiding mechanism (81 - 83; 91, 93, 101, 102; 131, 132, 134a, 134b, 135a, 135b) comprising a resilient member (81, 82; 91; 131, 132); for guiding said lens unit (1, 1a - 1c; 31; 84a, 84b; 94a, 94b; 100, 100a - 100c) such that said lens unit (84a, 84b; 94a, 94b; 100, 100a - 100c) can be moved in the direction of its optical axis (X) with respect to said lens barrel (87; 97; 105); and an electromagnetic induction coil (85, 86; 95, 96; 136, 137) and a magnetic member (89; 99; 133a, 133b) constituting a driving means for driving said lens unit (84a, 84b; 94a, 94b; 100, 100a to 100c) with respect to the lens barrel (87; 97; 105) by electromagnetic induction, said electromagnetic induction coil (85, 86; 95, 96; 136, 137) being coupled to one of the lens unit (84a, 84b; 94a, 94b; 100, 100a - 100c) and the lens barrel (87; 97; 105), and said magnetic member (89; 99; 133a, 133b) being coupled to the other of the lens unit (84a, 84b; 94a, 94b; 100, 100a - 100c) and the lens barrel (87; 97; 105); said apparatus being characterized in that detecting means (88; 98; 141, 142, 145, 146) are provided for detecting the relative position or the relative motion between said lens unit (84a, 84b; 94a, 94b; 100, 100a to 100c) and said lens barrel (87; 97; 105), said detecting means (88; 98; 141, 142, 145, 146) being arranged to carry out said detection by detecting strain of said resilient member (81, 82; 91; 131, 132). An apparatus according to claim 1, characterized in that said detecting means (88; 98; 141, 142, 145, 146) for detecting strain of said resilient member (81, 82; 91; 131, 132) include a strain gauge. An apparatus according to claim 1, characterized in that said resilient member (131,132) comprises two opposing surfaces, and said detecting means (141, 142, 145, 146) for detecting strain of said resilient member (131, 132) include two strain gauges for detecting strains of the opposing surfaces of said resilient member (131, 132). An optical apparatus according to any of the preceding claims 1 to 3, characterized by a further lens unit movable in the direction of its optical axis (x) and arranged within said lens barrel (87; 97; 105), the optical axis of said further lens unit being in common with the optical axis (x) of said lens unit (84a, 84b; 94a, 94b; 100, 100a - 100c); and a further driving means for driving said further lens unit relative to said lens barrel (87; 97; 105). An optical apparatus according to claim 4, characterized in that said lens unit (84a, 84b; 94a, 94b; 100, 100a - 100c) varies the focal length of an objective lens, and said further lens unit compensates for the movement of the image plane. An optical apparatus according to claim 4, characterized in that said further lens unit is used for focusing.

Inventors: MURAKAMI JUNICHI, OGINO SHIGERU, SEKINE MASAYOSHI, SUDA SHIGEYUKI, TAKAHARA HIROYUKI, TOKUMITSU JUN, TOYAMA MASAMICHI, TSUJI SADAHIKO, MURAKAMI, JUNICHI, OGINO, SHIGERU, SEKINE, MASAYOSHI, SUDA, SHIGEYUKI, TAKAHARA, HIROYUKI, TOKUMITSU, JUN, TOYAMA, MASAMICHI, TSUJI, SADAHIKO, MURAKAMI, JUNICHI, CANON KABUSHIKI KAISHA, OGINO, SHIGERU, CANON KABUSHIKI KAISHA, SEKINE, MASAYOSHI, CANON KABUSHIKI KAISHA, SUDA, SHIGEYUKI, C/O CANON KABUSHIKI KAISHA, TAKAHARA, HIROYUKI, C/O CANON KABUSHIKI KAISHA, TOKUMITSU, JUN, C/O CANON KABUSHIKI KAISHA, Toyama, Masamichi, c/o Canon Kabushiki Kaisha, Tsuji, Sadahiko, c/o Canon Kabushiki Kaisha
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1991
Main classification: G02B7
IPC codes: G02B7