A position recovery apparatus for inner focus lens

Abstract: The device has a feed screw (3) coupled to a stepping motor (2) and a moving member (4) is provided along the feed screw (3). The moving member (4) includes a rack (7) that is meshed with the feed screw (3). The moving member (4) has a lens supporting member (9) secured to its lower end, and a light emitting element (13) and a slit (4), are fixed to the lens supporting member (9). A semiconductor position detecting element (15) is secured within a lens housing in association with the slit (14). If the position of a lens (L) is fluctuated by a shock or the like when or after an image is properly focused, the distance in which a light passed through the slit (14) from the light emitting element (13) is moved on the semiconductor position detecting element (15) is electrically converted to drive the motor (2), and the lens (L) is thereby recovered to the properly-focused position. The number of teeth of the feed screw in which the teeth are skipped when the rack is disengaged is determined precisely. Then, the lens is moved by the distance corresponding to the fluctuated amount and is returned to the properly-focused position.

Description: BACKGROUND OF THE INVENTION Field of the invention: The present invention generally relates to apparatus for adjusting a focal length of a lens in a video tape recorder (VTR) having a built-in camera or the like and, more particularly, to a focus adjustment apparatus that can detect a lens position with accuracy. Description of the Related Art: Most of focus adjustment apparatus is small in size and generally comprises a feed screw disposed in an optical axis direction of a lens and a lens supporting member that can be moved forwardly and backwardly in accordance with the rotation of the feed screw or the like. According to the conventional focus adjustment apparatus of this type, after the lens is set to the initial position by energizing a reset switch, the feed screw is rotated by a motor to move the lens supporting member having the lens secured thereto forwardly or backwardly, thereby effecting the focus adjustment. In this conventional focus adjustment apparatus, 30% to 50% of a load applied to the motor when the lens is being focused in the zoom lens mode is used as a pressure to enable the rack and the feed screw to be operated in a satisfactory meshed condition. Although the above conventional focus adjustment apparatus is relatively small in size, it can endure a shock of about 1009 if the above pressure for enabling the rack to be satisfactorily meshed with the feed screw is selected to be sufficiently large. However, if the focus adjustment apparatus is increased twice in size, then the weight thereof is considerably increased, e.g., 8 times the original weight when proportioned simply. As a consequence, in proportion to the increased weight of the focus adjustment apparatus, a load applied to the motor also is increased, requiring a drive force of the motor to be increased. If the above pressure at which the rack can be satisfactorily meshed with the feed screw upon operation is increased, then the torque of the motor that rotates the feed screw must be increased. On the other hand, if such pressure is decreased, then the rack is easily disengaged from the screw thread of the feed screw even by a very small shock. There is then the disadvantage that the rack and the feed screw is not meshed with each other (hereinafter referred to as a so-called idle running phenomenon between the rack and the feed screw). If such idle running occurs between the rack and the feed screw, then a power switch of the focus adjustment apparatus must be turned off and then the focus adjustment apparatus must be again powered by actuating the reset switch because the focus adjustment apparatus is not provided with a position sensor that senses the lens position. There is known from EP-A-0 459 408 an optical lens controlling system in which a number of lens elements are separately driven and controlled through respective actuators and position sensors. A general control circuit is disclosed for controlling each of the lenses in a steady state, the control circuit being capable of performing initialisation for the respective lenses by parallel processing during an initial state before the steady state is reached so as to achieve quick initialisation or reset of a relatively complex camera lens assembly. OBJECTS AND SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide an improved focus adjustment apparatus in which the aforesaid shortcomings and disadvantages encountered with the prior art can be eliminated. More specifically, it is an object of the present invention to provide a focus adjustment apparatus in which a pressure sufficient so that a rack can be meshed satisfactorily with a feed screw is constantly applied to the rack under a certain condition so that, even when a lens is moved over a screw thread of a feed screw due to a shock or the like, such moved amount of the lens can be detected to thereby readily recover the lens to a properly-focused position. It is another object of the present invention to provide a focus adjustment apparatus in which a torque of a motor can be made small. It is still another object of the present invention to provide a focus adjustment apparatus which can be miniaturized. It is a further object of the present invention to provide a focus adjustment apparatus in which an overall electric power consumption can be reduced. According to a first aspect of the present invention, there is provided a focus adjustment apparatus having a lens provided so that said lens can be moved along a feed screw coupled to a rotary shaft of a motor wherein a focus is adjusted by the movement of said lens, comprising position detecting means for detecting a position of said lens ; and recovery means for displacing said lens to a previous position of said lens, characterised in that said recovery means are responsive to a spurious movement of said lens detected by said position detecting means and resulting from a disengagement of said feed screw and said rotary shaft due to an external mechanical shock, for moving said lens by an amount compensating for the spurious movement detected by said position detecting means so that said lens can be returned to the original position thereof just prior to said spurious movement. In accordance with a second aspect of the present invention, there is provided a video camera having a lens as defined above. According to the focus adjustment apparatus of the present invention, if the position of the lens supporting member is disengaged from the feed screw by an external shock or the like and the lens is fluctuated from the properly-focused position during or after the lens was located at the properly-focused position, then the fluctuated amount of the lens is detected by the lens position detecting member and the motor is thereby driven to recover the lens to the original properly-focused position. When the lens position detecting member is formed of the light emitting element, the slit and the semiconductor position detecting element, the amount by which the light passed through the slit from the light emitting element is moved on the semiconductor position detecting element is electrically detected to drive the motor, thereby correcting the lens position. BRIEF DESCRIPTION OF THE DRAWINGS A better understanding of other objects, features, and advantages of the present invention can be gained from a consideration of the following detailed description of an illustrative embodiment thereof, in conjunction with the figures of the accompanying drawings, in which: Figure 1 is a schematic perspective view showing a focus adjustment apparatus according to an embodiment of the present invention; Figure 2 is a perspective view showing a moving member used in the focus adjustment apparatus shown in Figure 1 in an enlarged scale; and Figure 3 is a block diagram showing the focus adjustment apparatus according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A focus adjustment apparatus according to an embodiment of the present invention will hereinafter be described with reference to Figures 1 to 3. As shown in Figure 1 of the accompanying drawings, a focus adjustment apparatus that is generally designated by reference numeral 1 comprises a feed screw 3 coupled to a rotary shaft of a stepping motor 2, a moving member 4 provided so as to move along the feed screw 3, a rack 7 attached to the moving member 4 so as to become meshed with the feed screw 3, a lens supporting member 9 secured to the lower end of the moving member 4, and a lens position detecting member 12 disposed between the fixing side into which the lens supporting member 9 is accommodated and the lens supporting member 9. The feed screw 3 is disposed above the lens L in the same direction as the optical axis direction of the lens L similarly to the example of the prior art. As shown in Figure 2, the moving member 4 has a pair of arms 5, 6 of substantially C-letter configuration (as seen from the front) coupled on its upper portion. Racks 7, 7 are respectively formed on the insides of the arms 5, 6 and a pressing member 8 is erected between the arms 5, 6. A spring S is engaged with the pressing member 8, whereby the feed screw 3 is pressed by the pressing member 8 from the lateral side under a force of the spring S. The moving member 4 is fitted into the upper portion of the lens supporting member 9 which will be described later on. The lens supporting member 9 has an insertion aperture 9a formed on its uppermost end and an insertion slit 9b formed on its lowermost end. An upper rail 10 is inserted into the insertion aperture 9a and a lower rail 11 is inserted into the insertion slit 9b so that each of the upper and lower rails 10, 11 can be freely slid in the front and rear direction. The above-mentioned fixed side is made immovable regardless of the movement of the lens L. In this embodiment, the inner surface portion (not shown) of the lens housing is utilized as the fixed side. As shown in Figure 3, the position detecting element 12 of the lens L comprises a light emitting element 13 such as a light emitting diode (LED) or the like, a slit 14 disposed on the optical path of the light emitting element 13, a semiconductor position detecting element 15 for detecting a light passed through the slit 14 from the light emitting element 13 or the like. The slit 14 is fixed to the side portion of the above lens supporting member 9 and the light emitting element 13 is fixed to the upper portion of the slit 14. The semiconductor position detecting element 15 has photo-detecting elements arrayed in the same direction as that of the slit 14. The full length of the semiconductor position detecting element 15 is a little longer than the length in which the lens supporting member 9 is moved, as shown in Figure 1. The semiconductor position detecting element 15 is fixed to the lens housing (not shown) in parallel to the lower rail 11. The focus adjustment apparatus 1 according to this embodiment further includes a driver 16 for driving the stepping motor 2, an analog-to-digital (A/D) converter 17 for converting an analog signal supplied thereto from the semiconductor position detecting element 15 into a digital signal, a microcomputer 18 for calculating a signal fluctuation amount to control the driver 16, a reset switch 19 for resetting the lens supporting member 9 to a predetermined initial position or the like. A focus adjustment operation by the focus adjustment apparatus 1 according to this embodiment will be described below. When the stepping motor 2 is actuated by the driver 16 to rotate the feed screw 3, the lens supporting member 9 is translated and then stopped at the properly-focused position of the lens L. If the above-mentioned idle running phenomenon occurs between the rack 7 of the moving member 4 and the feed screw 3 due to the external shock or the like during or after the lens L was located at the properly-focused position, then the lens supporting member 9 is moved during a period in which the idle running phenomenon occurred between the rack 7 and the feed screw 3. This moved amount of the lens supporting member 9 is detected by the position detecting member 12 of the lens L and then thereby corrected. More specifically, a light passed through the slit 14 of the lens supporting member 9 from the light emitting element 13 is moved on the semiconductor position detecting element 15 by a duration of period in which the above idle running phenomenon occurs. Then, the moved amount of the light is supplied through the A/D converter 17 to the microcomputer 18 as the change of a voltage, whereby the stepping motor 2 is driven during a time period of the idle running phenomenon between the rack 7 and the feed screw 3 to correct the fluctuated amount of the lens L. As described above, according to this embodiment, even when the focus of the lens L is fluctuated by a shock or the like, the fluctuated amount can be readily corrected without actuating the reset switch 19. Therefore, the focus adjustment apparatus of this embodiment can be best suited for, in particular, the focus adjustment of the inner focus type lens in which the feed screw 3 and the rack 7 are meshed with each other by a relatively small amount. The above optical and electrical lens position detecting member 12 composed of the light emitting element 13, the slit 14, the semiconductor position detecting element 15 or the like may be replaced with an arrangement that electrically converts the change of a magnitude of a magnetic force to thereby detect the fluctuated amount of the lens position. As set out above, according to the focus adjustment apparatus of the present invention, when the motor is utilized, the moving amount of the moving member and the lens supporting member can be set to be considerably large, for example, about 0.2 to 0.4 mm per revolution of the motor. Also, even when the idle running phenomenon occurs between the rack and the feed screw, the idle running amount between the rack and feed screw can be clearly determined. Thus, by moving the moving member and the lens supporting member by the fluctuated amount, the lens can be recovered to the properly-focused position. Consequently, according to the embodiment of the present invention, the torque of the motor can be made small, the overall dimension of the apparatus can be reduced and the electric power consumption of the whole of the apparatus can be reduced.

Claims: A focus adjustment apparatus having a lens (L) provided so that said lens can be moved along a feed screw (3) coupled to a rotary shaft of a motor (2) wherein a focus is adjusted by the movement of said lens, comprising : position detecting means (13, 14, 15) for detecting a position of said lens ; and recovery means (16, 17, 18) for displacing said lens to a previous position of said lens, characterised in that said recovery means (16, 17, 18) are responsive to a spurious movement of said lens (L) detected by said position detecting means (13, 14, 15) and resulting from a disengagement of said feed screw and said rotary shaft due to an external mechanical shock, for moving said lens by an amount compensating for the spurious movement detected by said position detecting means so that said lens can be returned to the original position thereof just prior to said spurious movement. The focus adjustment apparatus according to claim 1, further comprising a lens supporting member (9) for supporting said lens (L), and a moving member provided on said supporting member and having a rack (7) meshed with said feed screw. The focus adjustment apparatus according to claim 2, further comprising a rail (10,11) extended in the same direction as the direction of said feed screw and an insertion portion into which said rail is inserted so that said lens supporting member can be moved on said rail. The focus adjustment apparatus according to claim 3, wherein said lens position detecting means comprises a light emitting element (13) provided on said lens supporting member, a slit (14) disposed in an optical path of said light emitting element, and a photo-detecting elements (15) or detecting a light passed through said slit from said light emitting element. The focus adjustment apparatus according to claim 4, further comprising a driver (16) for driving said motor (2), an analog-to-digital (A/D) converter (17) for converting an output of said photo-detecting element (15) into a digital signal, and a microcomputer (18) for calculating said amount of movement of said lens on the basis of an output from said A/D converter to thereby control said driver. The focus adjustment apparatus according to claim 5, further comprising a reset switch (19) for setting said lens supporting member (9) to a predetermined initial position. The focus adjustment apparatus according to claim 6, wherein said focus adjustment apparatus is a focus adjustment apparatus of inner focus type. A video camera equipped with a lens as claimed in any one of claims 1 to 7. A method of controlling a lens (L) that is displaced to a focus position by means of a feed screw (3) coupled to the rotary shaft of a motor (2), comprising the steps of : detecting the position of said lens ; and recovering a previous position of said lens ; characterised in that said recovering step involves : determining the occurrence of a spurious movement of said lens resulting from a disengagement of said feed screw and said rotary shaft due to an external mechanical shock, and moving said lens by an amount compensating for the detected spurious movement so as to thereby return said lens to the original position thereof just prior to said spurious movement.

Inventors: HOSHINO MITSUO, TAKANO ATSUSHI, HOSHINO, MITSUO, TAKANO, ATSUSHI, HOSHINO, MITSUO C/O SONY CORPORATION, TAKANO, ATSUSHI C/O SONY CORPORATION
Applicants: SONY CORP, SONY CORPORATION
Application year: 1993
Main classification: G02B7
IPC codes: G02B7, H04N5