Camera lens barrel

Abstract: A camera lens barrel having a first grouped lens (1), a movable second grouped lens (2) for variable magnification, a third grouped lens (3) and a fourth grouped lens (4), which are respectively arranged along an optical axis, and accommodating a drive system for the first to fourth lenses. The camera lens barrel is provided with a stepping motor (10), a control device capable of carrying out at least micro step drive control of the stepping motor (10) and a moving mechanism (14) for converting rotation of the stepping motor (10) into movement of the second grouped lens (2) along the optical axis. The control device carries out position control of the second grouped lens (2) according to a control quantity of the stepping motor (10). As the stepping motor (10) is driven under the micro step drive control, the generation of noise and vibration can be greatly suppressed as compared with a conventional lens barrel employing a DC motor as a drive source.

Description: CAMERA LENS BARREL BACKGROUND OF THE INVENTION The present invention relates to a camera lens barrel in a video camera or the like. More particularly, this invention relates to a driving device for a zoom lens in a camera lens barrel of an inner focus type having a four-group zoom lens system with an autofocus function and a motor-driven zoom function. In a video camera having an autofocus function and a zoom function, it is increasingly demanded to have a more compact and handier construction as well as an improvement in performance. To this end, various attempts have been made to improve upon a camera lens barrel in a video camera (e.g., as shown in Japanese Patent Laid-open Publication No. 1-196011 and Japanese Patent Application No. 2-130580 entitled "Camera Lens Barrel" filed by the Applicant of the present application). A zoom lens system consisting of four groups of lenses is known as a lens system to be accomodated in a camera lens barrel. Such a four-group zoom lens system may be of two types. One type is afrontfocus type such that a first grouped lens, a second grouped lens and a third grouped lens of the four groups of lenses are adapted to be moved. The other type is an inner focus type such that a fourth grouped lens of the four groups of lenses has a focusing function, a correcting function and an imaging function, and that the second grouped lens and the fourth grouped lens are adapted to be moved. The present invention relates particularly to the latter inner focus type of a zoom lens system. In a conventional camera lens barrel of the inner focus type, the second grouped lens for zooming to provide a variable magnification is moved in a direction of an optical axis along two guide shafts fixed to the lens barrel by using a DC motor, a reduction gear for reducing a rotating speed of the DC motor, and a cam, since a moving quantity of the second grouped lens is large. On the other hand, the fourth grouped lens for imaging is driven by a voice coil motor which is linearly operated. However, when driving the second grouped lens by using the DC motor, the reduction gear, and the cam as mentioned above, there are many problems such as the generation of noise to an electronic circuit in the video camera, generation of vibration in driving, low reliability of a brush of the DC motor, a difficulty in high-speed zooming, and a difficulty in providing a compact construction. SUMMARY OF THE INVENTION It is accordingly an object of the present invention to provide a camera lens barrel which can suppress noise and vibration. It is another object of the present invention to provide a camera lens barrel which can ensure a high reliability. It is a further object of the present invention to provide a camera lens barrel which can realize a high-speed zoom operation. It is a still further object of the present invention to provide a camera lens barrel which can be made compact. The present invention applies specifically to a camera zoom lens barrel having, in the order of proximity with respect to the object side, a first group lens a second group lens arranged movably to vary magnification, a fixed third lens group, and a fourth grouped lens arranged movably to focus, which are respectively arranged along an optical axis, and accommodating a drive system for said second and fourth lenses, comprising : a first drive motor; control means capable of controlling said first drive motor; a moving mechanism arranged to convert rotation of said first drive motor into movement of said second grouped lens along said optical axis; and a second drive motor arranged to drive said fourth grouped lens, wherein said control means provides position control of said second grouped lens by calculating a position of said second grouped lens on the basis of the amount of rotation said first drive motor has made, taken from an end position of said second grouped lens. Such an arrangement is known e.g. from EP-A-0 394 901. According to the invention, the first drive motor is a stepper motor, and said camera zoom lens barrel further comprises a mode switch for selecting a high-speed drive mode or a low-speed drive mode, wherein when the high-speed drive mode is selected, said control means carries out pulse drive control of said stepping motor, while when the low speed drive mode is selected, said control means carries out a micro step drive control of said stepping motor. When the low-speed drive mode is selected, the stepping motor is driven at low speeds by the control means under the micro step drive control, thus suppressing the vibration and noise during the movement of the second grouped lens. Accordingly, when the second grouped lens is moved, the vibration and noise are suppressed by enabling the stepping motor to be driven under the micro step drive control. No complex position sensor for detecting a position of the second grouped lens is required, and the lens barrel is therefore reduced in size by utilizing a control quantity of the stepping motor for the detection of the position of the second grouped lens. Based on the concept of the present invention, the stepping motor can be driven under the micro step drive control, and the second grouped lens is moved by the stepping motor and the moving mechanism to be operated in response to the rotation of the stepping motor. Further, a position of the second grouped lens is calculated from a control quantity of the stepping motor. That is, the inner focus type camera lens barrel according to the present invention comprises a stepping motor which can be driven at least under the micro step drive control, control means, and a moving mechanism for moving the second grouped lens along the optical axis in response to the rotation of the stepping motor. As described above, according to the present invention, the second lens in the inner focus type camera lens barrel is moved by using a stepping motor. Accordingly, the movement of the second grouped lens can be smoothly effected to thereby suppress noise and vibration. In particular, by driving the stepping motor under the micro step drive control, the generation of noise and vibration can be almost eliminated. Further, since no complex sensor for detecting a position of the second grouped lens is required, the camera lens barrel can be made inexpensive, and it can be reduced in size. Further, as the drive system for the second grouped lens is simple, and in particular, a diametrical size of the camera lens barrel is small, the camera lens barrel can be made even more compact. Additionally, as the moving mechanism in the camera lens barrel does not employ any low-reliable members such as a brush, the reliability can be improved. Other objects and features of the invention will be more fully understood from the following detailed description and appended claims when taken with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an exploded perspective view of a camera lens barrel according to a preferred embodiment of the present invention; and Fig. 2 is a block diagram illustrating a control system according to the preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described with reference to the drawings, in which Fig. 1 is an exploded perspective view of an inner focus type camera lens barrel according to the preferred embodiment of the present invention, and Fig. 2 is a block diagram illustrating a control system for controlling a stepping motor for driving a second grouped lens and a focus linear motor for driving a fourth grouped lens. The camera lens barrel shown in Fig. 1 is provided with a first grouped lens 1, a second grouped lens 2, a third grouped lens 3, and a fourth grouped lens 4, which are arranged in series along an optical axis. There is provided a charge coupled device (CCD) 5 as an imaging device at a focus position of the fourth grouped lens 4. The first grouped lens 1 is a focusing lens group constituted of a plurality of lenses, e.g. two lenses, which are fixed in the camera lens barrel. The second grouped lens 2 is a zoom lens group for variable magnification constituted of a plurality of lenses, e.g., three lenses, which are movable along the optical axis. The movement of the second grouped lens 2 will be hereinafter described in detail. The third grouped lens 3 is a correcting lens group constituted of a plurality of lenses, e.g., two lenses, which are fixed in the camera lens barrel. Further, the fourth grouped lens 4 is an imaging lens group constituted of a plurality of lenses, e.g. two lenses, which are movable along the optical axis by a focusing linear motor 18. A fixed plate 15 is provided between the first grouped lens 1 and the third grouped lens 3, both of which are fixed. A stepping motor 10 for moving the second grouped lens 2 is provided between the fixed plate 15 and the third grouped lens 3. The fixed plate 15 is provided with a through hole having a center coincident with the optical axis. There is provided adjacent to the fixed plate 15 an iris 8 for opening and closing the through hole of the fixed plate 15. An iris driving motor 9 for vertically driving the iris 8 is provided between the fixed plate 15 and the third grouped lens 3. A frame 6 for the second grouped lens 2 is provided with a tapped hole 16 for engaging a lead screw 14. The lead screw 14 is mounted on an outer surface of a rotary shaft 13 of the stepping motor 10 for moving the second grouped lens 2, and is threadedly inserted through the tapped hole 16 of the frame 6. The rotary shaft 13 is adapted to be rotated by driving the stepping motor 10, and the frame 6 of the second grouped lens 2 is adapted to be moved back and forth on a first reference shaft 11 along the optical axis by the rotation of the lead screw 14 and the engagement thereof with the tapped hole 16. In order to ensure precise movement of the frame 6 of the second grouped lens 2 along the optical axis, a second reference shaft 12 as a guide is fixed to the fixed plate 15. Accordingly, the second grouped lens 2 is adapted to be moved back and forth along the optical axis as being guided by the second reference shaft 12. Further, in order to prevent the second grouped lens 2 from colliding with the first grouped lens 1, the first reference shaft 11 is fixed to the second grouped lens 2. The first reference shaft 11 is inserted through the fixed plate 15 so as to be movable relative thereto. An end point sensor 7 is fixed to a front end of the first reference shaft 11. The end point sensor 7 is formed from a Hall device for detecting that the front end of the first reference shaft 11 has contacted a rear end of the first grouped lens 1, so as to detect an initial position of the second grouped lens 2. When the front end of the first reference shaft 11 comes into contact with the rear end of the first grouped lens 1, the end point sensor 7 generates a signal of logic "1", while when the front end of the first reference shaft 11 is free from contact with the rear end of the first grouped lens 1, the end point sensor 7 generates a signal of logic "0". As mentioned above, the stepping motor 10 is provided between the fixed plate 15 and the third grouped lens 3. When setting a moving distance D1 of the second grouped lens 2 to about 20 mm, the stepping motor 10 is sized to have a diameter of about 10 mm and a length of about 12 mm, thus permitting sufficient accommodation thereof in the lens barrel. Further, since the rotary shaft 13 and the lead screw 14 mounted thereon are provided in connection with the stepping motor 10 so as to extend along the optical axis, the lens barrel can be reduced in diameter. In addition, since the end point sensor 7 is provided at the front end of the first reference shaft 11 to detect only the initial position of the second grouped lens 2, a sufficient space can be ensured in the lens barrel. It is further advantageous that the end point sensor 7 for detecting the initial position of the second grouped lens 2 need not be an expensive sensor because the structure thereof is so simple as to only detect the contact of the first reference shaft 11 with the first grouped lens 1. The iris 8 is adapted to be moved vertically by the iris driving motor 9 to open or close the through hole of the fixed plate 15. The fourth grouped lens 4 is adapted to be moved by the focusing linear motor 18, and a position of the fourth grouped lens 4 is detected by a position sensor 17. The position sensor 17 is constituted of a detecting portion 17a formed from a Hall device and a driving portion 17b. The position sensor 17 is a sensor for continuously detecting the position of the fourth grouped lens 4. Drive control of the stepping motor 10 and the focus linear motor 18 is provided by the control system shown in Fig. 2. The control system includes a control circuit 22 having a microcomputer, a control data memory 23 such as a RAM, and driver circuits 24 and 25, which are connected together as illustrated. In this preferred embodiment, the stepping motor 10 is driven by a two-phase bipolar driving method. This driving method includes a pulse drive (e.g. a one-phase-on pulse drive, a two-phase-on pulse drive, or a half-step drive) and a two-phase sin/cos drive (e.g., a micro step pulse drive). In the pulse drive, a large torque can be obtained, and a high-speed operation of the stepping motor 10 can be effected. However, noise and vibration are somewhat large. In the micro step drive, a large torque cannot be obtained, and a high-speed operation of the stepping motor 10 cannot be effected. However, less noise and vibration are generated. Accordingly, this preferred embodiment effectively utilizes the above advantages of the pulse drive and the micro step drive. That is, when operating the second grouped lens 2 at high speeds, the stepping motor 10 is controlled to be driven in a pulse drive mode, while when operating the second grouped lens 2 at low speeds, the stepping motor 10 is controlled to be driven in a micro step drive mode. The control system includes a mode switch 21 for selecting either the pulse drive mode or the micro step drive mode. When the mode switch 21 is operated to select a high-speed drive terminal HIGH, a "high" level signal of a supply voltage Vcc is input into the control circuit 22, while when the mode switch 21 is operated to select a low-speed drive terminal LOW, a "low" level signal or an earth voltage is input into the control circuit 22. The control circuit 22 accommodates a program for executing the pulse drive for the stepping motor 10 and a program for executing the micro step drive for the stepping motor 10. The control data memory 23 includes a trapezoidal control data memory section 231 and a micro step control data memory section 232 for respectively storing data to be used in executing the pulse drive and the micro step drive. That is, a control signal data having a trapezoidal waveform to be applied to the stepping motor 10 for the pulse drive is stored in the trapezoidal control data memory section 231. On the other hand, a sin/cos control data for the micro step drive of the stepping motor 10 is stored in the micro step control data memory section 232. The control circuit 22 controls a zoom position of the second grouped lens 2 through the stepping motor 10, the rotary shaft 13, the lead screw 14, the tapped hole 16 as a moving mechanism, and the second reference shaft 12. A position data of the zoom position of the second grouped lens 2 in an initial stage thereof is based on a signal of logic "1" to be output from the end point sensor 7 upon detecting that the front end of the first reference shaft 11 fixed to the second grouped lens 2 has contacted the first grouped lens 1. After receiving the logic "1" signal from the end point sensor 7, the control circuit 22 updates the position data of the zoom position of the second grouped lens 2 on the basis of a control quantity of the stepping motor 10. That is, since the stepping motor 10 carries out a precise stepping operation in response to a pulse control command from the control circuit 22, the control circuit 22 sequentially tracks and accumulates the control quantity output to the stepping motor 10, thereby calculating a present position of the second grouped lens 2. Accordingly, no complex and precise position sensor for detecting the position of the second grouped lens 2 is required as previously mentioned. In this way, the control circuit 22 receives from the end point sensor 7 the logic "1" signal indicating a reference position of the second grouped lens 2, and updates and grasps the present position of the second grouped lens 2 on the basis of a control quantity output to the stepping motor 10. Thereafter, when a contact 27 is closed to demand a zoom operation, the control circuit 22 provides a moving control of the second grouped lens 2 to be described below. When the low-speed drive terminal LOW of the mode switch 21 is selected, the control circuit 22 carries out the micro step drive control of the stepping motor 10 through the driver circuit 24 by using the data stored in the micro step control data memory section 232 of the control data memory 23 according to the micro step control program. Under the micro step drive control, the stepping motor 10 is driven in the micro step mode, and it is rotated slowly. Accordingly, the rotary shaft 13 is slowly rotated to thereby move the frame 6 of the second grouped lens 2 forward or reverse at low speeds through the lead screw 14. Thus, the second grouped lens 2 is moved forward or reverse at low speeds along the optical axis as being guided by the second reference shaft 12. This operation is continued while the zoom operation is demanded. When the high-speed drive terminal HIGH of the mode switch 21 is selected, the control circuit 22 carries out the pulse drive control of the stepping motor 10 by using the data stored in the trapezoidal control data memory section 231 of the control data memory 23 according to the pulse drive control program. As a result, the stepping motor 10 is rotated at high speeds to thereby move the second grouped lens 2 at high speeds. As mentioned above, when selecting the low-speed drive terminal LOW, the stepping motor 10 is operated at low speeds to move the second grouped lens 2 at low speeds. In this case, the generation of noise and vibration is suppressed. In contrast, when selecting the high-speed drive terminal HIGH, the second grouped lens 2 is moved at high speeds, and the noise and vibration become larger than those in the micro step mode. However, since this preferred embodiment does not employ a brush of a DC motor, a reduction gear, and a cam as used in the conventional DC motor drive, the noise and vibration in the pulse drive mode according to the preferred embodiment can be made less than those in the prior art. Further, since the movement of the second grouped lens 2 is effected by the stepping motor 10 having no brush in this preferred embodiment, a high reliability can be ensured. Additionally, the control circuit 22 carries out an electronic cam control of both the second grouped lens 2 and the fourth grouped lens 4. In the electronic cam control, the second grouped lens 2 and the fourth grouped lens 4 are interlocked to effect a zoom and autofocus control as a whole. To realize the electronic cam control, the control circuit 22 accommodates an electronic cam control program. Further, position data to be used for the electronic cam control is stored and updated in an electronic cam data memory section 233 of the control data memory 23. The control circuit 22 calculates control quantities of the stepping motor 10 and the focusing linear motor 18 according to the electronic cam control program, and outputs the calculated control quantities through the driver circuits 24 and 25 to the stepping motor 10 and the focusing linear motor 18, respectively. In this way, the drive control of the focusing linear motor 18 is carried out in association with the drive control of the stepping motor 10. The above-mentioned electronic cam control is applicable to both the pulse drive and the micro step drive of the stepping motor 10. It is to be understood that the present invention is not limited to the above preferred embodiment which is merely illustrative, but various modifications may be made within the scope of the invention. For instance, the end point sensor 7 may be so arranged as to detect that the first reference shaft 11 has contacted the third grouped lens 3. Further, the rotary shaft 13, the lead screw 14 and the tapped hole 16 constituting the moving mechanism may be replaced by any other means enabling the rotation of the stepping motor 10 to be converted into the linear movement of the second grouped lens 2 along the optical axis. While the above-mentioned preferred embodiment has been specifically applied to a video camera, the camera lens barrel of the present invention may be applied to any other similar apparatus such as a camera having a zoom function.

Claims: A camera zoom lens barrel having, in the order of proximity with respect to the object side, a first lens group (1), a second lens group (2) arranged movably to vary magnification, a fixed third lens group (3), and a fourth lens group (4) arranged movably to focus, which are respectively arranged along an optical axis, and accommodating a drive system for said second and fourth lenses (2 and 4), comprising : a first drive motor (10); control means (22) capable of controlling said first drive motor (10); a moving mechanism (14) arranged to convert rotation of said first drive motor (10) into movement of said second grouped lens (2) along said optical axis; and a second drive motor (18) arranged to drive said fourth grouped lens (4), wherein said control means (22) provides position control of said second grouped lens (2) by calculating a position of said second grouped lens (2) on the basis of the amount of rotation said first drive motor (10) has made, taken from an end position of said second grouped lens (2), characterized in that said first drive motor is a stepper motor (10), and in that said camera zoom lens barrel further comprises a mode switch (21) for selecting a high-speed drive mode or a low-speed drive mode, wherein when the high-speed drive mode is selected, said control means (22) carries out pulse drive control of said stepping motor (10), while when the low speed drive mode is selected, said control means (22) carries out a micro step drive control of said stepping motor (10). The camera lens barrel according to claim 1, wherein the pulse drive control is a one-phase-on pulse drive, a two-phase-on pulse drive or a half-step drive control. The camera lens barrel according to claim 1, wherein the micro step drive control is a two-phase sin/cos drive control. The camera lens barrel according to claim 1, wherein said control means is a control system comprising : a control circuit (22) having a microcomputer; a control data memory (23) comprising a micro step control data memory section (232) for said micro step drive control and a trapezoidal control data memory section (231) for said pulse drive control; and a driver circuit (24) for connecting said control circuit to said stepping motor (10).

Inventors: INOUE NORIKATSU C O SONY CORPO, KAWAMURA HIROSHI C O SONY CORP, NAKAYAMA AKIHITO C O SONY CORP, NAKAZATO KUNIO C O SONY CORPOR, INOUE, NORIKATSU, C/O SONY CORPORATION, KAWAMURA, HIROSHI, C/O SONY CORPORATION, NAKAYAMA, AKIHITO, C/O SONY CORPORATION, NAKAZATO, KUNIO, C/O SONY CORPORATION
Applicants: SONY CORP, SONY CORPORATION
Application year: 1991
Main classification: G02B7
IPC codes: G02B7