Lens barrel and image pickup apparatus with a mechanism for absorbing an external impact

A lens barrel includes an extendable barrel unit, a drive unit configured to drive the barrel unit so as to extend the barrel unit, and a transmission unit configured to transmit a drive force of the drive unit to the barrel unit, the transmission unit includes a first gear and a second gear coaxially disposed and a biasing member configured to bias at least one of the first gear and the second gear such that the drive force is transmitted between the first gear and the second gear, and the transmission unit is configured to block transmission of the drive force between the first gear and the second gear depending on a rotational force applied to at least one of the first gear and the second gear.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lens barrel and an image pickup apparatus including a clutch mechanism that absorbs an impact from an outside of the lens barrel or the image pickup apparatus.

2. Description of the Related Art

Conventionally, a lens barrel and an image pickup apparatus capable of changing a focal length of an image pickup lens by extending each lens unit that constitute the image pickup lens toward an object side have been known. For example, when an external impact is applied to the lens barrel in an extended state of the image pickup lens, an excess load is applied to a gear that constitutes a transmission mechanism of a drive force. In this time, cogs of the gear may be chipped off and thus a stable operation of the lens barrel may be difficult.

Accordingly, a lens barrel which mounts a mechanism (an impact absorption mechanism) to prevent damages of the gear has been known. Commonly, the transmission mechanism of the drive force is configured to couple a motor with a barrel unit via a two-stage gear, and thus the drive force of the motor is transmitted to the barrel unit while the two-stage gear reduces the speed of the drive force.

Japanese Patent Laid-open No. 2002-195313 discloses an overload clutch device using a coil spring as an impact absorption mechanism. Specifically, the coil spring is disposed in a space provided inside one gear of two gears that constitute a two-stage gear. In this configuration, when a great force is applied to the gear, the gear spins out and thus the damages of the gear can be prevented. On the other hand, Japanese Patent Laid-open Nos. 2002-276693 and 2003-315655 disclose configurations of using a plate spring and a C-shaped spring instead of the coil spring.

However, in the configuration disclosed in Japanese Patent Laid-open No. 2002-195313, it is necessary to dispose the coil spring inside the gear, and thus the size of a clutch mechanism is enlarged. In addition, it is necessary to provide a member to prevent the coil spring from being released from the gear. In the configurations disclosed in Japanese Patent Laid-open Nos. 2002-276693 and 2003-315655, the plate spring and the C-shaped spring are disposed inside the gear, and thus the degree of freedom of designing the spring is small and it is difficult to achieve a stable clutch operation.

SUMMARY OF THE INVENTION

The present invention provides a lens barrel and an image pickup apparatus capable of performing a stable operation without increasing in size of a clutch mechanism.

A lens barrel as one aspect of the present invention includes an extendable barrel unit, a drive unit configured to drive the barrel unit so as to extend the barrel unit, and a transmission unit configured to transmit a drive force of the drive unit to the barrel unit, the transmission unit includes a first gear and a second gear coaxially disposed and a biasing member configured to bias at least one of the first gear and the second gear such that the drive force is transmitted between the first gear and the second gear, and the transmission unit is configured to block transmission of the drive force between the first gear and the second gear depending on a rotational force applied to at least one of the first gear and the second gear.

An image pickup apparatus as another aspect of the present invention provides an image pickup element configured to photoelectrically convert an optical image to output an image signal and the lens barrel.

DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments of the present invention will be described below with reference to the accompanied drawings.

First of all, referring toFIGS. 1 to 4, an image pickup apparatus including a lens barrel in the embodiment will be described.FIG. 1is an external perspective view of an image pickup apparatus (digital camera18) including a lens barrel when viewed from a front side.FIG. 2is an external perspective view of the digital camera18ofFIG. 1in a state where the power of the digital camera18is turned on.FIG. 3is a back view of the digital camera18, andFIG. 4is a bottom view of the digital camera18. In the digital camera18of the embodiment, a lens barrel19(barrel unit) is capable of extending when the power is turned on (at the time of capturing an image).

As illustrated inFIGS. 1 and 2, the digital camera18of the embodiment includes a zoom mechanism that moves a lens unit between an image capturing position (extended position) and a retracted position in an optical axis direction to change a photographing magnification. At a front surface of the digital camera18, a finder16that determines a composition of an object, an auxiliary light source15that is used to perform photometry and focus detection, a strobe17, and the lens barrel19(barrel unit) are provided. At an upper surface of the digital camera18, a release button12, a power switching button14, and a zoom switch13are provided. As illustrated inFIG. 3, at the back surface of the digital camera18, operating buttons22to27, a display21such as an LCD, and a finder eyepiece20are provided. As illustrated inFIG. 4, at the bottom surface of the digital camera18, a tripod mounting unit28, a memory card drive42(seeFIG. 5), and a cover of a battery insertion unit (not illustrated) are provided.

Subsequently, referring toFIG. 5, a control configuration of the image pickup apparatus (digital camera18) will be described.FIG. 5is a control block diagram of the digital camera18. A bus44is connected to a CPU46, a ROM45, a RAM47, the release button12, the operating buttons22to27, the display21, the power switching button14, the zoom switch13, a memory40, a compression and expansion unit41, the memory card drive42, and a drive circuit43.

The drive circuit43is connected to a zoom mechanism30that drives the lens barrel19via a zoom motor5, a focus drive mechanism31that drives a focus lens57, a shutter drive mechanism32that drives a shutter35, and an aperture stop drive mechanism34that drives an aperture stop36. The drive circuit43is also connected to an image pickup element58such as a CCD sensor or a CMOS sensor, and the strobe17. The image pickup element58photoelectrically converts an optical image (object image) to output an image signal. The drive control of each unit that is connected to the drive circuit43is performed based on a signal from the CPU46via the drive circuit43.

The ROM45stores various control programs. The RAM47stores data required for the various control programs. An analog signal processing unit37performs analog processing for image data outputted from the image pickup element58, and outputs the processed data to an A/D converter38. The A/D converter38converts analog data obtained from the image pickup element58to digital data, and outputs the digital data to a digital signal processing unit39. The digital signal processing unit39performs predetermined processing for the digital data converted by the A/D converter38, and outputs the data as image data to the memory40.

The compression and expansion unit41performs compression processing such as JPEG or TIFF for the image data stored in the memory40based on the operation of the operating button23. After the compression and expansion unit41performs the compression processing for the image data, the processed data are outputted and stored in a memory card that is attached to the memory card drive42. The compression and expansion unit41performs expansion processing for the image data stored in the memory40or the image data stored in the memory card. After the expansion processing is performed for the image data, the display21(display unit) is capable of displaying the image data via the bus44. A user see the image displayed on the display21, and can delete the image by the operation of the operating button24when the user determines that the image is not necessary.

Next, referring toFIG. 6toFIGS. 12A to 12C, the lens barrel19of the embodiment will be described.FIG. 6is a perspective view of the lens barrel19in an image capturing state (an extended state).FIG. 7is a perspective view of the lens barrel19in a state where a fixed cylinder1and a gear cover3(housing unit) are removed.

InFIG. 7, when the zoom motor5is driven by the drive circuit43and the zoom mechanism30(seeFIG. 5), a first gear6attached to the zoom motor5rotates. In the embodiment, the drive circuit43, the zoom mechanism30, and the zoom motor5constitute a drive unit that drives the lens barrel19(barrel unit) to be extended.

A rotational force (torque) of the first gear6is transmitted to a second gear7, a first clutch gear (first gear), a second clutch gear9(second gear), a fourth gear10, and a fifth gear11in this order. Based on a rotational force transmitted to the fifth gear11, a cam cylinder4of the lens barrel19rotates. Accordingly, a follower4aof the cam cylinder4moves in a direction of an optical axis OA (in the optical axis direction) along a cam groove (not illustrated) provided on an inner surface of the fixed cylinder1, and thus the lens barrel19is in the photographing state. In the embodiment, the first gear6, the second gear7, a third gear (the first clutch gear8, the second clutch gear9, and a spring100described below), the fourth gear10, and the fifth gear11constitute a transmission mechanism (transmission unit) of a barrel drive force. In this configuration, the transmission unit transmits the drive force of the drive unit (the drive circuit43, the zoom mechanism30, and the zoom motor5) to the barrel unit (cam cylinder4).

In the image capturing state illustrated inFIG. 6, when a load (impact force, or external force) in a compression direction (optical axis direction) is applied to the lens barrel19by falling the digital camera18carelessly or the like, the cam cylinder4tries to move in a retracting direction while rotating along the cam groove. In this time, the rotational force is transmitted from the fifth gear11to the zoom motor5. In many case, however, the strength of the barrel drive unit (power transmission unit) is set to the minimum strength required to withstand the drive force of the zoom motor5in order to reduce the size of the lens barrel19. Therefore, when the rotational force not less than the drive force of the zoom motor5is applied to the barrel drive unit, there is a possibility that elements such as gears which constitute the barrel drive unit are damaged.

FIG. 8is an exploded perspective view of the lens barrel19(barrel drive unit). The first gear6as a worm gear is attached to the zoom motor5. A blade portion6afor detecting the number of rotations is provided at an end of the first gear6. The blade portion6a, a first photo sensor attached to the gear cover3, and a second photo sensor attached to a barrel plate2enable detecting the number of rotations of the zoom motor5. An image pickup element58(seeFIG. 5) is attached to the barrel plate2. The second gear7is disposed next to the first gear6, and a worm portion6bof the first gear6and a large gear portion of the second gear7are provided so as to engage with each other. A clutch mechanism (third gear) is disposed next to the second gear7, and a small gear portion of the second gear7and the first clutch gear8are provided so as to engage with each other. In the embodiment, the clutch mechanism (third gear) is configured by the first clutch gear8, the second clutch gear9, and the plate spring100.

The fourth gear10is disposed next to the clutch mechanism, and the second clutch gear9and a large gear portion of the fourth gear10are provided so as to engage with each other. The fifth gear11is disposed next to the fourth gear10, and a small gear portion of the fourth gear10and the fifth gear11are provided so as to engage with each other. The fifth gear11is disposed so as to engage with a gear portion4bprovided on the cam cylinder4. The gear cover3is provided so as to cover each gear. The plate spring100(biasing member) is provided on an upper surface of the gear cover3. The gear cover3and the plate spring100are integrally connected to the barrel plate2by using a screw. Alternatively, the plate spring100may be formed integrally with the gear cover3.

FIG. 9is a perspective view of the first clutch gear8.FIG. 10is a perspective view of the second clutch gear9.FIGS. 11A and 11Bare cross-sectional views of the clutch mechanism. In the embodiment, the clutch mechanism is configured by the first clutch gear8, the second clutch gear9, and the plate spring100. As illustrated inFIG. 9, a convex portion8a(first clutch gear convex portion) and a concave portion8b(first clutch gear concave portion) are formed on the first clutch gear8. A drive shaft8d(first clutch gear drive shaft) is integrally formed at the center of the first clutch gear8. A slope portion8c(first clutch gear slope portion) which is set at an arbitrary angle is formed between the convex portion8aand the concave portion8bof the first clutch gear8. The convex portions8aand the concave portions8bare alternately provided circumferentially centered around the drive shaft8d.

As illustrated inFIG. 10, a convex portion9a(second clutch gear convex portion) and a concave portion9b(second clutch gear concave portion) are formed on the second clutch gear9. A hole portion9d(second clutch gear hole portion) is formed at the center of the second clutch gear9. The convex portions9aand the concave portions9bare alternately provided circumferentially centered around the hole portion9d. A slope portion9c(second clutch gear slope portion) which is set at an arbitrary angle is formed between the convex portion9aand the concave portion9b.

As illustrated inFIGS. 11A and 11B, the clutch mechanism is configured by the first clutch gear8, the second clutch gear9, and the plate spring100. In the embodiment, the plate spring100is disposed outside the first clutch gear8, the second clutch gear9, and the gear cover3. Therefore, the size of the clutch mechanism (the first clutch gear8and the second clutch gear9) can be reduced. In addition, since the space to provide the plate spring100can be sufficiently ensured, the degree of freedom of designing the spring is improved and a stable clutch operation is possible. Furthermore, since the plate spring100can remove a backlash of the gear, it contributes to reduction of the noise of the barrel drive unit.

FIG. 11Ais a cross-sectional view of the clutch mechanism in a driving state of the lens barrel19. In the driving state of the lens barrel19, the drive shaft8dof the first clutch gear8is inserted into the hole portion9dof the second clutch gear9. In this state, the convex portion8aof the first clutch gear8fits into the concave portion9bof the second clutch gear9, and the convex portion9aof the second clutch gear9fits into the concave portion8bof the first clutch gear9. In this case, the plate spring100biases (urges against) a bearing portion8f(first clutch gear bearing portion) of the first clutch gear8which is integrally coaxially formed on the drive shaft8dof the first clutch gear8. In this configuration, the first clutch gear8and the second clutch gear9are integrally rotated by the drive (rotational force) of the zoom motor5. In the embodiment, preferably, the bearing portion8fis formed hemispherically in order to reduce a sliding load on the plate spring100.

FIG. 11Bis a cross-sectional view of the clutch mechanism in a clutch working state. When an impact force (load, or external force) is applied to an end of the lens barrel19as illustrated inFIG. 6, the cam cylinder4rotates and the rotational force from the cam cylinder4is transmitted to the fifth gear11and the fourth gear10in this order. The rotational force transmitted to the fourth gear4is transmitted to the second clutch gear9. In this case, a relative position between the first clutch gear8and the second clutch gear9is shifted so as to increase the distance between the first clutch gear8and the second clutch gear9by a height of the convex portion8aof the first clutch gear or the convex portion9aof the second clutch gear9. In this case, as indicated by an arrow inFIG. 11B, the plate spring100is elastically deformed by the height of the convex portion9aof the second clutch gear9. As a result, the fitting of the first clutch gear8and the second clutch gear9is released, and the second clutch gear9spins out. In this configuration, the rotational force transmitted from the cam cylinder4is not transmitted to the first gear6. Therefore, the damage of the barrel drive unit can be effectively avoided.

Subsequently, referring toFIGS. 12A to 12C, the operation of the clutch mechanism will be described.FIGS. 12A to 12Care schematic diagrams of illustrating the operation of the clutch mechanism.FIG. 12Ais a schematic diagram of the clutch mechanism at the time of driving based on the rotational force by the zoom motor5(in the driving state of the lens barrel19). In this time, the first clutch gear8is biased (energized) in a direction of the second clutch gear9(a downward direction inFIG. 12A) by a biasing force of the plate spring100. Therefore, the slope portion8cof the first clutch gear8contacts the slope portion9cof the second clutch gear9, and the first clutch gear8and the second clutch gear9integrally rotate.

FIG. 12Bis a schematic diagram of the clutch mechanism at the time of starting the operation. When the impact force (load) is applied to the end of the lens barrel and the rotational force of the fourth gear10is transmitted to the second clutch gear9as indicated by an arrow inFIG. 12B, the slope portion8cof the first clutch gear8is moved up by the slope portion9cof the second clutch gear9. In the embodiment, when the rising force of the first clutch gear8indicated by the arrow inFIG. 12Bis larger than the biasing force of the plate spring100indicated by an arrow inFIG. 12A, the clutch mechanism operates. Therefore, the biasing force of the plate spring100is set to be larger than the rising force of the first clutch gear8which is generated by the rotational force of the zoom motor5. This is because the clutch mechanism operates in the driving state of the lens barrel19, i.e. at the time of rotation by the drive of the zoom motor5, when for example the biasing force of the plate spring100is smaller than the rising force of the first clutch gear8which is generated by the rotational force of the zoom motor5.

FIG. 12Cis schematic diagram of the clutch mechanism during its operation. The slope portion8cof the first clutch gear8moves along the slope portion9cof the second clutch gear9, and the first clutch gear8moves away from the second clutch gear9. Then, the convex portion8aof the first clutch gear8runs on the convex portion9aof the second clutch gear9. Repeating the operations described above, the clutch mechanism operates.

Thus, in the embodiment, the transmission unit includes the first clutch gear8(a first gear) and the second clutch gear9(a second gear) both of which are coaxially disposed. Furthermore, the transmission unit includes the plate spring100(biasing member) which biases (urges against) the first clutch gear8so as to transmit the drive force between the first clutch gear8and the second clutch gear9. In this configuration, the transmission of the drive force between the first clutch gear8and the second clutch gear9is blocked depending on the rotational force which is applied to the second clutch gear9. For example, the rotational force occurs in the second clutch gear9by the external force applied to the lens barrel19(barrel unit).

In the embodiment, preferably, the rotational force generates a reaction force (rising force) which is larger than the biasing force of the biasing member (plate spring100) for the first clutch gear8and thus the transmission of the drive force between the first clutch gear8and the second clutch gear9is blocked. More preferably, the biasing member biases (urges against) the first clutch gear8such that the first clutch gear8and the second clutch gear9engage with each other. When the reaction force is applied, the first clutch gear8and the second clutch gear9are configured so as to release the engagement between the first clutch gear8and the second clutch gear9. Preferably, the first clutch gear8and the second clutch gear9constitute a two-stage gear. Preferably, the biasing member is elastically deformed by the reaction force, and thus the first clutch gear8and the second clutch gear9are configured so as to move away from each other in a rotational axis direction.

Preferably, the first clutch gear8includes the drive shaft8d, and the plurality of convex portions8aand concave portions8balternately provided around the drive shaft8d. The second clutch gear9includes the hole portion9d, and the plurality of convex portions9aand concave portions9balternately provided around the hole portion9d. The first clutch gear8and the second clutch gear9engage with each other by insertion of the drive shaft8dof the first clutch gear8into the hole portion9dof the second clutch gear9. More preferably, the slope portions8cand9care formed between the plurality of convex portions8aand9aand the plurality of concave portions8band9b, respectively. Preferably, the first clutch gear8includes an end portion (bearing portion8f) of the drive shaft8dwhich is provided at a side opposite to the second clutch gear9. The biasing member biases the end portion (bearing portion8f) of the drive shaft8d, and thus the first clutch gear8is biased. More preferably, the end portion (bearing portion8f) of the drive shaft8dis formed hemispherically.

Preferably, the lens barrel further includes the gear cover3(housing unit) which covers the first clutch gear8and the second clutch gear9. The biasing member, which is a plate elastic member, is attached to the gear cover3or is formed integrally with the gear cover3.

According to the embodiment, a lens barrel and an image pickup apparatus capable of performing a stable operation without increasing in size of a clutch mechanism can be provided.

For example, the lens barrel of the embodiment is configured to be integrally with the image pickup apparatus (digital camera18) including the image pickup element58, but is not limited to this configuration. The embodiment is applicable also to a lens barrel which is configured separately from an image pickup apparatus. In the embodiment, the plate spring100is configured to bias the first clutch gear8, but is not limited to this configuration. Alternatively, the plate spring may be configured to bias the second clutch gear9instead of the first clutch gear8. In this case, the second clutch gear9moves away from the first clutch gear8depending on the rotational force generated by the external force.

This application claims the benefit of Japanese Patent Application No. 2013-248882, filed on Dec. 2, 2013, which is hereby incorporated by reference herein in its entirety.