ELECTRIC TOOL

Abstract

The present disclosure provides a technique for improving the user-friendliness of an electric tool. The electric tool comprises a motor, a spindle, and a planetary gear mechanism. The spindle rotates due to a torque transmitted by the motor. The planetary gear mechanism transmits the torque from the motor to the spindle. An axis of rotation of the motor and an axis of rotation of the spindle are arranged on the same straight line. The planetary gear mechanism comprises a sun gear, a plurality of planet gears, a carrier, and an internal gear. The torque from the motor is applied to the sun gear. The multiple planet gears are arranged on a radial outer side around an axis of rotation of the sun gear. The carrier is fixed so as not to rotate relative to the housing and supports the multiple planet gears such that they are rotatable on their own axes.The internal gear is rotatably mounted on the outer side of the multiple planetary gears and transmits the rotational force of the spindle.

Description

TECHNICAL AREA The present disclosure relates to an electric tool. BACKGROUND Among electric tools that incorporate a planetary gear mechanism as a speed reduction device, there are electric tools in which the rotational axis of a motor and the rotational axis of a spindle are arranged on the same straight line, and such an electric tool employs a configuration that uses the planetary gear mechanism in a planetary operating mode. In the case where the planetary gear mechanism is used in the planetary operating mode, a rotational force is input from the motor into a sun gear (a central gear). An internal gear (a ring gear) is fixed. A planet gear rotates about its own axis and rotates. A driving force is output by a carrier (a planetary carrier) that supports the planet gear (e.g., disclosed in JP 4 457 170 B1). BRIEF SUMMARY In a power tool that uses a planetary gear mechanism, the motor and the tool body rotate in the same direction. In other words, the spindle, to which the rotational force is transferred from the tool body, also rotates in the same direction as the motor. Specifically, in impact tools with a hammer that delivers a blow in one direction, components such as the motor, tool body, spindle, hammer, and anvil rotate in the same direction. In such a power tool, the moments of inertia of the components rotating in the same direction increase at the start of operation and at the moment of stopping. This causes the main body of the power tool to vibrate in a direction opposite to the motor's rotation.Consequently, one of the user's hands is shaken, and a heavy load is applied at the start of operation of the electric tool and at the time of stopping the electric tool. A non-limiting objective of the present disclosure is to provide an improvement that contributes to a reduction in the load imposed on a user at the time of work using an electric tool. The above-mentioned problem is solved by an electric tool according to claim 1 or claim 9. A non-limiting aspect of the present disclosure provides for an electric tool comprising a motor, a spindle, a planetary gear mechanism, and a housing. The spindle rotates due to a torque transmitted by the motor. The planetary gear mechanism transmits the torque from the motor to the spindle. The housing accommodates at least part of the planetary gear mechanism. An axis of rotation of the motor and an axis of rotation of the spindle are arranged on the same straight line. The planetary gear mechanism comprises a sun gear, a plurality of planet gears, a carrier, and an internal gear. The torque from the motor is applied to the sun gear. A plurality of planet gears are arranged on a radially outer side about an axis of rotation of the internal gear. The carrier is fixed non-rotatably relative to the housing and supports the plurality of planet gears rotatably about their own axes.The internal gear is rotatably arranged on the radially outer side of most planetary gears and transmits the rotational force to the spindle. According to the present design, the planetary gear mechanism is configured to operate in a star configuration, where the carrier is fixed and non-rotatable. In this configuration, the motor, internal gear, and spindle rotate in opposite directions to each other. Consequently, the moment of inertia due to the motor's rotation cancels out the moment of inertia due to the rotation of the internal gear and spindle, effectively suppressing the undesirable vibration of the power tool's main body caused by inertial forces at the start and stop of operation.Therefore, the present aspect can reduce a load placed on a user at the time of work using the electric tool, thereby improving the usability of the electric tool. The term "axis of rotation of the motor" and "axis of rotation of the spindle" being arranged on the same straight line is not limited to the requirement that the axes of rotation of the motor and the axes of rotation of the spindle are arranged completely on the same straight line. It also includes the requirement that the axes of rotation of the motor and the axes of rotation of the spindle are arranged substantially on the same straight line. Furthermore, it includes the requirement that the axes of rotation of the motor and the axes of rotation of the spindle are slightly misaligned from the straight line due to a manufacturing defect, a gap between axes of rotation, looseness, or play. Another, non-limiting aspect of the present disclosure provides for an electric tool comprising a motor and a spindle. The spindle rotates due to a torque transmitted by the motor. An axis of rotation of the motor and an axis of rotation of the spindle are arranged parallel to each other or on the same straight line. The motor and the spindle rotate in opposite directions. According to this design, the motor and spindle rotate in opposite directions. Therefore, the moment of inertia due to the motor's rotation and the moment of inertia due to the spindle's rotation cancel each other out, effectively suppressing the unwanted vibration of the power tool's main body caused by these inertial moments at startup and when the tool stops. Consequently, this design reduces the load placed on the user during operation, thus improving the tool's usability. The term "parallel axis of rotation of the motor" and "parallel axis of rotation of the spindle" is not limited to the condition that the motor and spindle axes are perfectly parallel. It also encompasses situations where the motor and spindle axes are substantially parallel. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a striking tool according to a first embodiment. Fig. 2 is a vertical cross-sectional view of the striking tool. Fig. 3 is a vertical cross-sectional view showing an upper region of the striking tool. Fig. 4 is a perspective view of a power transmission mechanism of the striking tool. Fig. 5 illustrates the relationship between a planetary gear mechanism and a spindle. Fig. 6 shows the configurations of the planetary gear mechanism and the spindle. Fig. 7 is a perspective exploded view of the planetary gear mechanism and the spindle. Fig. 8 illustrates the relationship between the spindle and an internal hammer. Fig. 9 is a schematic configuration drawing of a striking tool according to a second embodiment. DETAILED DESCRIPTION OF THE EXECUTION FORMS The following description details representative and non-limiting specific examples of the present invention with reference to the drawings. This detailed description is intended solely to provide a person skilled in the art with details of the implementation of preferred examples of the present invention and is not intended to limit the scope of the present invention. Furthermore, the additional features and inventions disclosed below can be used separately or together with other features and inventions to provide further improved devices and methods for their manufacture and use. Furthermore, combinations of features and steps disclosed in the following detailed description are not necessary to carry out the present invention in its broadest sense, but merely serve to describe representative specific examples of the present invention. Moreover, various features of the representative examples described above and those listed below, as well as various features listed in the independent and dependent claims below, need not necessarily be combined in the specific ways or sequences illustrated herein to provide additional and useful embodiments of the present invention. In one or more non-restrictive embodiments according to the present disclosure, the electric tool may further comprise a carrier fixing component configured to fix the carrier non-rotatably to the housing. According to this embodiment, the carrier cannot be rotatably fixed to the housing via the carrier fixing component. Therefore, the carrier can be securely fixed, preventing rotation of the planetary gears, which are subject to a strong rotational force from the motor (the sun gear). Consequently, the rotational force of the sun gear can be transmitted to the inner gear without being attenuated by the planetary gears or the carrier. In addition to or instead of the embodiments described above, the internal gear and the spindle can be configured as separate individual components. According to this embodiment, the internal gear and the spindle can be manufactured more easily compared to a configuration where the internal gear and the spindle are formed as a single integrated component. Furthermore, this embodiment facilitates the use of different materials for these components compared to a configuration where the internal gear and the spindle are formed as a single integrated component. In addition to or instead of the embodiments described above, the internal gear and the spindle are connected in a manner that allows relative movement in an axial direction along an axis of rotation of the internal gear and the spindle. According to this embodiment, the transmission of vibration generated in the axial direction of the axis of rotation from the spindle to the internal gear can be suppressed when the electric tool is driven. Consequently, the durability of the planetary gear mechanism can be improved. In addition to or instead of the embodiments described above, the internal gear and the spindle are connected via a splined connection that extends in the axial direction of the axis of rotation of the internal gear and the spindle. According to this embodiment, the electric tool can have a structure characterized by excellent power transmission capability exerted in the direction of rotation from the internal gear to the spindle and excellent self-alignment capability, while simultaneously suppressing the transmission of vibration generated by the spindle in the axial direction of the axis of rotation when the electric tool is driven. In addition to or instead of the embodiments described above, the support fixing component can have a gear-shaped first engagement area on which a plurality of teeth are formed circumferentially around the axis of rotation of the sun gear. The housing can have a second engagement area that is compatible with the first engagement area. According to this embodiment, the carrier fixing component is fixed to the housing due to the circumferential gear shape, and this can facilitate the housing absorbing the force of the carrier in the direction of rotation. Consequently, the carrier can be securely fixed to the housing indirectly. In addition to or instead of the embodiments described above, the support can be a metal component. The support fixing component can be a synthetic resin component. According to this embodiment, while the strength of the support to which the force from the planetary gears is transmitted can be improved by designing it as a metal component, the strength of the support fixing component can be reduced by designing it as a synthetic resin component. In addition to or instead of the embodiments described above, the electric tool may have a hammer arranged around the spindle and rotatable in the same direction as the spindle due to the spindle's rotational force. The electric tool may also have an anvil arranged at least partially at the front of the spindle and configured to be struck by the hammer in a rotational direction. According to this embodiment, the moment of inertia due to the rotation of the motor and the moment of inertia due to the rotation of the hammer can cancel each other out, and this can help to suppress such a phenomenon that the main body of the electric tool is undesirably shaken in the direction of rotation at the beginning of operation and at the time of stopping, thereby improving the usability of the electric tool. In addition to or instead of the embodiments described above, an electric tool comprising a motor and a spindle can be used. The spindle can rotate due to the torque transmitted by the motor. The motor's axis of rotation and the spindle's axis of rotation can be parallel to each other or aligned on the same straight line. The motor and the spindle can rotate in opposite directions to each other. According to this embodiment, the motor and the spindle rotate in opposite directions. Therefore, this embodiment allows the moment of inertia due to the rotation of the motor and the moment of inertia due to the rotation of the spindle to cancel each other out, thus successfully suppressing the phenomenon of undesirable vibration of the main body of the power tool due to the moments of inertia at the start of operation and when the power tool stops, thereby improving the usability of the power tool. In addition to or instead of the embodiments described above, the electric tool may have a planetary gear mechanism configured to transmit the motor's torque to the spindle. The planetary gear mechanism may include a sun gear, a planet gear, a carrier rotatably mounted on the planet gear's own axis, and an internal gear. The motor's torque can be input into the sun gear. The carrier can be fixed in a non-rotatable position. The internal gear can be rotatable. Torque from the internal gear can be output to the spindle. According to this embodiment, the planetary gear mechanism is configured to operate in a star configuration, with the carrier fixed in a non-rotatable manner. In this star configuration, the motor's direction of rotation is opposite to that of the internal gear and the spindle. Consequently, this embodiment allows the moment of inertia due to the motor's rotation and the moments of inertia due to the rotation of the internal gear and the spindle to cancel each other out. This effectively suppresses the phenomenon of undesirable vibrations of the power tool's main body due to inertial vibrations at the start and stop of operation, thus improving the power tool's usability. A. First embodiment As an example of an electric tool according to a representative and non-limiting embodiment of the present disclosure, a striking tool 1 is described in detail with reference to the drawings. First, the configuration of the striking tool 1 is described. Then, the operation of the striking tool 1 is described. Configuration of impact tool The configuration of the impact tool 1 is described with reference to Fig. 1, Fig. 2 to Fig. 3. In the present embodiment, the impact tool 1 is an impact wrench. The impact tool 1 is an electric tool that performs screw tightening by rotating an anvil 81 while simultaneously striking a tool accessory (e.g., a screwdriver bit) inserted into this anvil 81 in a rotational direction. Specifically, when the user operates and presses a trigger lever 26, which is an actuating unit located on a handle area 22 of the impact tool 1, electrical power from a battery pack 10 is supplied to a motor 40 via a controller 29, causing a rotor 44 provided by the motor 40 to rotate. The torque output from the motor 40 is transmitted to a spindle 60 via a planetary gear mechanism 50, which serves as a speed reduction device. The torque transmitted to the spindle 60 is then transferred to the anvil 81 via an internal hammer 78, which is part of an impact mechanism 70.The rotation of the anvil 81 causes the tool accessory inserted into the anvil 81 to rotate, thereby performing the screw tightening operation. If resistance is encountered in the direction of rotation between a screw and a workpiece, and a predetermined or greater load is applied to the anvil 81 during the tightening operation, an impact force is applied to the anvil 81 by the inner hammer 78 and an outer hammer 73, which are parts of the striking mechanism 70. The anvil 81 rotates the screw while the rotational force and the impact force are applied to the screw in the direction of rotation. In this way, the striking tool 1 performs the screw tightening operation. In the present embodiment, a front-back direction is defined as a direction parallel to an axis of rotation AX of the motor 40. A front side and a rear side are defined as the side in the front-back direction on which the spindle 60 is arranged with respect to the motor 40, and the opposite side from the front side, respectively. A vertical direction is defined as the direction in which the grip area 22 extends in directions perpendicular to the axial direction of the axis of rotation AX. A bottom side and an upper side are defined as the side in the vertical direction on which the grip area 22 is arranged with respect to the motor 40, and the opposite side from the bottom side. A left-right direction of the impact tool 1 is defined as a direction perpendicular to the vertical direction and the front-back direction. The striking tool 1 comprises a main body housing 2, a rear cover 3, and a hammer housing 4. The main body housing 2 is made of a synthetic resin. The main body housing 2 is formed by a pair of semi-split housings, consisting of a right-hand housing and a left-hand housing. The right-hand housing and the left-hand housing are fixed together by means of a plurality of screws 2S. The main body housing 2 has a motor mounting area 21, a handle area 22 and a battery holding area 23. The motor mounting area 21 is tubular in shape and accommodates the motor 40. Furthermore, the motor mounting area 21 accommodates part of the hammer housing 4. The internal configuration of the motor mounting area 21 will be described later. The grip area 22 is gripped by the user when the impact tool 1 is in use. The grip area 22 extends downwards from the motor mounting area 21. The trigger lever 26 and a forward / reverse rotation selector lever 27 are located on the upper part of the grip area 22. The trigger lever 26 is an actuating unit that is operated by the user to activate the motor 40. When the trigger lever 26 is actuated by the user pressing it, the motor 40 is driven. When the user releases the actuating action on the trigger lever 26, the motor 40 is stopped. The forward / reverse rotation selector lever 27 is an actuating unit that is operated by the user to switch the direction of rotation of the motor 40 from one forward direction to the other.When the direction of rotation of the motor 40 is switched, the directions of rotation of the spindle 60 and the anvil 81 are switched. The battery holding area 23 is connected to the lower end of the grip area 22. The battery holding area 23 holds the battery pack 10 via a battery mounting area 28. The outer dimensions of the battery holding area 23 are larger than the outer dimensions of the grip area 22 in the front-back and left-right directions. The rear cover 3 is arranged such that it covers an opening at the rear end of the motor mounting area 21. The rear cover 3 is made of a synthetic resin. The rear cover 3 accommodates at least part of a fan wheel 31. Furthermore, the rear cover 3 accommodates a rear rotor bearing 32. The rear rotor bearing 32 rotatably supports the rear end of the rotor shaft 45, which is provided with the motor 40. The motor mounting area 21 has an intake opening 24. The rear cover 3 has an exhaust opening 25. Rotation of the fan wheel 31 causes air to flow from outside the main body housing 2 into the interior of the main body housing 2 via the intake opening 24. The air in the interior of the main body housing 2 flows out to a space outside the main body housing 2 via the exhaust opening 25. The fan wheel 31 is located between a stator 41 (the motor 40) and the rear rotor bearing 32. The fan wheel 31 is fixed to the rear portion of the rotor shaft 45 of the motor 40. When the motor 40 is activated, the fan wheel 31 rotates along with the rotor shaft 45, generating an airflow to cool the motor 40. The rotation of the fan wheel 31 causes air in the outer chamber of the main housing 2 to flow into the interior of the main housing 2 through the intake opening 24. The air introduced into the interior of the main housing 2 cools the motor 40 as it flows through the interior of the main housing 2. After flowing through the interior of the main housing 2, the air flows out into the outer chamber of the main housing 2 through the exhaust opening 25 due to the rotation of the fan wheel 31. Motor 40 is described with reference to Fig. 3. Motor 40 is a power source for the impact tool 1. Motor 40 is an internal rotor brushless motor. Motor 40 comprises stator 41 and rotor 44. The stator 41 is mounted in the motor mounting area 21. The stator 41 has a stator core 42 and a coil 43. At least part of the rotor 44 is located inside the stator 41. The rotor 44 rotates relative to the stator 41. The rotor 44 rotates about the axis of rotation AX, which extends in the front-back direction. The rotor 44 has the rotor shaft 45, a rotor core 46, a rotor magnet 47, and a sensor magnet 48. The rotor shaft 45 and the rotor core 46 are each made of steel. In this embodiment, the rotor shaft 45 and the rotor core 46 are integrated. The front portion of the rotor shaft 45 projects forward from the front end surface of the rotor core 46. The rear portion of the rotor shaft 45 projects rearward from the rear end surface of the rotor core 46. The rotor magnet 47 is fixed to the rotor core 46. In the present embodiment, the rotor magnet 47 is arranged around the rotor core 46. The sensor magnet 48 is fixed to the rotor core 46. In this embodiment, the sensor magnet 48 is arranged on the front end surface of the rotor core 46. A sensor board 49 is arranged at the front end of the stator 41. The sensor board 49 has an annular switching board and a rotation detection element mounted on the switching board. At least part of the sensor board 49 faces the front end surface of the sensor magnet 48. The rotation detection element detects the position of the rotor 44 in the direction of rotation by detecting the position of the sensor magnet 48. The rear end of the rotor shaft 45 is rotatably mounted by the rear rotor bearing 32. The rear rotor bearing 32 is held by the rear cover 3. A drive gear 58 is fixed to the front end of the rotor shaft 45. The rotor shaft 45 is connected to the planetary gear mechanism 50, which is the speed reduction device, via the drive gear 58. The drive gear 58 acts as a sun gear of the planetary gear mechanism 50. In other words, power (rotational force) from the motor 40 is input to the planetary gear mechanism 50 via the drive gear 58. The power from the motor 40 is output by the tool accessory via the power transmission mechanism, which comprises the planetary gear mechanism 50, the spindle 60, the impact mechanism 70, and the anvil 81. The power transmission mechanism, which transmits the power of the motor 40, is described with reference to Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7 to Fig. 8. The planetary gear mechanism 50 is described. The planetary gear mechanism 50 according to the present embodiment is configured to operate as a star type. Generally, a sun gear is rotatable in the case where the planetary gear mechanism operates as a star type. A planet gear can rotate on its own axis. A carrier that supports the planet gear is fixed so as not to rotate. Since the carrier that supports the planet gear is fixed so as not to rotate, the planet gear cannot rotate around the sun gear, even though it is rotatable on its own axis. An internal gear is rotatable. Now the configuration of the planetary gear mechanism 50 is described in detail. As shown in Fig. 4, the planetary gear mechanism 50 comprises a carrier fixing component 51, an O-ring 53, a carrier 55, gear shaft pins 56, planet gears 57, the drive gear 58 and an internal gear 59. An opening area 55A is formed on the central region of the support 55. A circular groove-shaped bearing fixing area 55B is formed on the central region of the rear side of the support 55 (Fig. 7). The opening area 55A and the bearing fixing area 55B are interconnected. The drive gear 58 extends through the opening area 55A. A front rotor bearing 33 is held by the bearing fixing area 55B from the rear side of the support 55. The front rotor bearing 33 acts as a bearing for the drive gear 58. As described above, the drive gear 58 is connected to the rotor shaft 45 of the motor 40. The power from the motor 40 is transmitted to the planetary gear mechanism 50 via the drive gear 58. The drive gear 58 functions as the sun gear of the planetary gear mechanism 50. Three planet gears 57 are arranged radially outside the axis of rotation of the drive gear 58. Each of the planet gears 57 is mounted on the carrier 55 such that it can rotate about its own axis due to the gear pin 56. The drive gear 58 and the three planet gears 57 mesh with each other. A rotation of the drive gear 58 causes each of the planet gears 57 to rotate, with the gear pin 56 serving as an axis of rotation for this rotation. A retaining area 51A, which is a through-hole, is formed by the carrier fixing component 51. The carrier 55 is held by being fitted into the retaining area 51A. In the present embodiment, the carrier 55 is a metal component, and the carrier fixing component 51 is a resin component. The strength of the carrier 55, to which a force is transmitted from the planetary gears 57, can be improved by designing it as a metal component. Furthermore, the weight of the carrier fixing component 51 can be reduced by designing it as a resin component. In the present embodiment, the carrier 55 and the carrier fixing component 51 are integrally formed by injection molding. A gear-shaped first engagement area 51B is formed on the circumferential edge region of the support fixing component 51. A second engagement area 4B, which fits onto the first engagement area 51B of the support fixing component 51, is formed on the hammer housing 4. A toothed area and a groove area in the front-back direction are formed on the second engagement area 4B. The support fixing component 51 is securely fixed by the interlocking engagement between the first engagement area 51B of the support fixing component 51 and the second engagement area 4B of the hammer housing 4 in such a way that rotation about the axis of rotation AX is prevented. Since the support fixing component 51 is fixed to the hammer housing 4, and the support 55 is fixed to the support fixing component 51, the support 55 is fixed so as not to rotate about the axis of rotation AX. In other words, the support 55 is fixed so as not to rotate relative to the hammer housing 4, which corresponds to the sun gear. Therefore, when the motor 40 is driven to rotate the drive gear 58, the three planet gears 57, which are supported by the support 55, rotate on their own axes but do not rotate around the sun gear (the drive gear 58). The O-ring 53 is positioned between the support fixing component 51 and the hammer housing 4. The interior of the hammer housing 4 is filled with a lubricant. The placement of the O-ring 53 between the support fixing component 51 and the hammer housing 4 prevents the lubricant from flowing out to the outside of the hammer housing 4 via a connection between the support fixing component 51 and the hammer housing 4. The internal gear 59 is arranged on the outside of the planet gears 57. The internal gear 59 is tubular. A flat surface is formed on the front side of the tubular section of the internal gear 59, and a circular opening 59B is formed on this flat surface. The internal gear 59 accommodates the three planet gears 57 inside its tubular section. The internal gear 59 has a gear formed on an inner wall 59A of the tubular section, which meshes with each of the three planet gears 57. When the motor 40 is driven to rotate the rotor shaft 45, the drive gear 58, which serves as the internal gear, rotates in the same direction as the rotor shaft 45. Due to the rotation of the drive gear 58, the three planet gears 57 rotate on their own axes, with the gear pins 56 serving as their axes of rotation. Simultaneously, the three planet gears 57 do not rotate. Furthermore, the internal gear 59 rotates on its own axes due to the rotation of the three planet gears 57. When viewed in the direction of the axis of rotation AX, the drive gear 58 and the internal gear 59 rotate in opposite directions. The internal gear 59 is rotatably connected to the spindle 60, which will be described later. In other words, the rotor 44 of the motor 40, the internal gear 59, and the spindle 60 rotate in opposite directions. Applying such a configuration allows the moment of inertia originating from the rotor 44 due to the rotation of the motor 40 and the moments of inertia due to the rotation of the internal gear 59 and the spindle 60 to cancel each other out when the impact tool 1 is driven, thus succeeding in suppressing the phenomenon of the main body of the electric tool 1 being undesirably shaken due to the moments of inertia at the start of operation of the electric tool 1 and at the time of stopping the electric tool 1. Furthermore, according to the present embodiment, the striking tool 1 comprises the outer hammer 73 and the inner hammer 78, which are described below. When the motor 40 rotates, the inner gear 59, the spindle 60, the outer hammer 73, and the inner hammer 78 rotate in the same direction. Therefore, when the striking tool 1 is driven, the moment of inertia originating from the rotor 44 due to the rotation of the motor 40 and the moments of inertia due to the inner gear 59, the spindle 60, the outer hammer 73, and the inner hammer 78 cancel each other out. This can help suppress the phenomenon of the main body of the striking tool 1 being undesirably shaken due to the moments of inertia at the start of operation and when the striking tool 1 stops.The impact tool 1 applies weights, shapes and design positions of components designed in such a way that the magnitude of the moment of inertia originating from the rotor 44 due to the rotation of the motor 40 and the magnitude of the moments of inertia due to the internal gear 59, the spindle 60, the outer hammer 73 and the inner hammer 78 are approximately equal. Furthermore, according to the present embodiment, the impact tool 1 does not have a component, such as a bearing, for aligning the axis of the internal gear 59. One reason for this is described below. The rotor shaft 45 is rotatably mounted by the rear rotor bearing 32. The drive gear 58, which is fixed to the rotor shaft 45, is rotatably mounted by the front rotor bearing 33. Therefore, the axis of rotation of the drive gear 58, which is connected to the rotor shaft 45, and the axis of rotation AX of the motor 40 coincide. In other words, the drive gear 58 is in an axially aligned state and is in such a state that the axis of rotation of the drive gear 58 is located in a suitable position. The planet gears 57 are also in an axial alignment state. Specifically, the axes of rotation of the planet gears 57 are arranged at suitable positions with the support of the carrier fixing component 51, the carrier 55 and the gear shaft pins 56. If the axes for two types of gears among the three types of gears (the sun gear, the planet gears, and the internal gear) in the planetary gear mechanism 50 are aligned, the axis of the remaining type of gear will also align itself without a bearing or the like, due to its self-aligning capability. In the present embodiment, two types of gears, namely the drive gear 58 (the sun gear) and the planet gears 57, are in a state of axial alignment. Therefore, the axis of rotation of the internal gear 59 coincides with the axis of rotation AX of the motor 40, even without the provision of a component, such as a bearing, intended for the axial alignment of the gear 59. In other words, according to the present embodiment, the impact tool 1 does not need to be provided with a bearing for the axial alignment of the internal gear 59.Therefore, according to the present embodiment, the impact tool 1 can achieve a simplification of the structures, a reduction in weight and a reduction in costs. The internal gear 59 has a connecting area 59C, used for connection with the spindle 60, at the circumferential edge of the opening area 59B. Conversely, the spindle 60 has a connecting area 60C for connection with the internal gear 59. The connecting area 59C of the internal gear 59 and the connecting area 60C of the spindle 60 are connected by a splined connection extending in the axial direction of the axis of rotation AX. In other words, the internal gear 59 and the spindle 60 are connected in such a way that they are relatively movable in the axial direction of the axis of rotation AX. This can suppress the transmission of vibration generated in the axial direction of the axis of rotation AX from the spindle 60 to the internal gear 59 when the impact tool 1 is driven. Consequently, the durability of the planetary gear mechanism 50 can be improved.Furthermore, the connection between the internal gear 59 and the spindle 60 via the splined connection can achieve a structure that is excellent in its ability to transmit the torque from the internal gear 59 to the spindle 60 and in its self-aligning capability. This is the configuration of the planetary gear mechanism 50. A further configuration of the power transmission mechanism for transmitting power from the motor 40 is described below. The spindle 60 is located at the front of the planetary gear mechanism 50. The spindle 60 rotates about the axis of rotation AX driven by the motor 40. The spindle 60 rotates due to the torque of the rotor 44, which is transmitted via the planetary gear mechanism 50. Specifically, the spindle 60 rotates due to the torque transmitted by the connecting section 59C, located at the internal gear 59 of the planetary gear mechanism 50, and the connecting section 60C, located on the spindle 60. The spindle 60 transmits the torque of the motor 40, transmitted by the planetary gear mechanism 50, to the impact mechanism 70, which will be described later. The spindle 60 has a spindle shank region 60A, a flange region 60B, a connection region 60C, a distal end opening region 60D, and spindle grooves 61. The spindle shank region 60A has a rod-like shape that is elongated in the front-back direction. The central axis of the spindle shank region 60A and the axis of rotation AX coincide. The flange region 60B extends radially outward from the rear end region of the outer circumferential surface of the spindle shank region 60A. A splined connection in the axial direction of the axis of rotation AX is formed on the circumferential edge of the side surface of the flange region 60B, which is the connection region 60C. As described above, the splined connection in the axial direction of the axis of rotation AX is also formed on the connection region 59C of the internal gear 59.The connecting area 59C of the internal gear 59 and the connecting area 60C of the spindle 60 are connected via the splined connection, which extends in the axial direction of the axis of rotation AX. The distal end opening region 60D is provided at the distal end of the spindle shaft region 60A. An anvil projection region 81D of the anvil 81, which is described below, is inserted into the distal end opening region 60D. The spindle 60 has spindle grooves 61 on the outer circumferential surface of the spindle shaft region 60A. Three spindle grooves 61 are provided on the outer circumferential surface of the spindle shaft region 60A. Each spindle groove 61 has a central spindle groove region 61A, a first spindle groove region 61B, and a second spindle groove region 61C. The central spindle groove region 61A is located at the front end of the spindle groove 61. The first spindle groove region 61B extends obliquely rearward from the central spindle groove region 61A toward one circumferential side. The second spindle groove region 61C extends obliquely rearward from the central spindle groove region 61A toward the other circumferential side. A ball 62 is arranged in each of the spindle grooves 61. Specifically, a ball 62 is arranged between each of the hammer grooves 79 provided on the inner hammer 78, which will be described later, and each of the spindle grooves 61.A rotational force from the spindle 60 is transmitted to the inner hammer 78 via the balls 62. The behavior of the balls 62 and the inner hammer 78 when the spindle 60 rotates will be described later. The striking mechanism 70 will now be described. The striking mechanism 70 is driven by the motor 40. The rotational force of the motor 40 is transmitted to the striking mechanism 70 via the planetary gear mechanism 50 and the spindle 60. The striking mechanism 70 strikes the anvil 81 in the direction of rotation based on the rotational force of the spindle 60, which is driven by the motor 40. The striking mechanism 70 comprises a spiral retaining ring 71, a bracket 72, the outer hammer 73, balls 73F, balls 73G, a first coil spring 74, a second coil spring 75, a washer 76, a bearing coil spring 77, and the inner hammer 78. The inner hammer 78 strikes the anvil 81 in the direction of rotation about the axis of rotation AX. The inner hammer 78 is mounted on the spindle 60. The inner hammer 78 is arranged around the spindle shaft area 60A. The inner hammer 78 comprises a hammer body section 78A, hammer projection sections 78B, and hammer grooves 79. The hammer body section 78A is tubular. The hammer body section 78A is arranged around the spindle shaft section 60A. The hammer projection sections 78B are located on the front section of the hammer body section 78A. The hammer projection sections 78B project forward from the front section of the hammer body section 78A. Two hammer projection sections 78B are arranged around the axis of rotation AX. The hammer body region 78A has a plurality of hemispherical recess regions 78C along the circumference of the outer wall. The inner hammer 78 has a plurality of spheres 78D. The spheres 78D are made of metal. One sphere 78D is arranged in each of the recess regions 78C. Specifically, the plurality of spheres 78D are arranged between the inner hammer 78 and the outer hammer 73 and transmit a rotational force from the inner hammer 78 to the outer hammer 73. Three hammer grooves 79 are formed on the inner wall of the hammer body region 78A. Each of the hammer grooves 79 has a shape that narrows at the rear and widens towards the front. A hammer groove 79 has a central hammer groove region 79A located at the rear end of the hammer groove 79, a first hammer groove region 79B extending from the central hammer groove region 79A to one circumferential side, and a second hammer groove region 79C extending from the central hammer groove region 79A to the other circumferential side. As described above, a ball 62 is arranged between each of the three spindle grooves 61 and each of the three hammer grooves 79. The rotational force of the spindle 60 is transmitted to the inner hammer 78 via the balls 62. The behavior of the balls 62 and the inner hammer 78 when the spindle 60 rotates will be described later. The outer hammer 73 is arranged around the inner hammer 78. The outer hammer 73 is tubular. The outer hammer 73 is arranged such that it surrounds the axis of rotation AX. The outer hammer 73 rotates together with the inner hammer 78 in the direction of rotation around the axis of rotation AX. The outer hammer 73 increases the moment of inertia of the striking mechanism 70 by rotating together with the inner hammer 78. The outer hammer 73 has a tubular section 73A, a stepped section 73B, and a rear end surface section 73C. The tubular section 73A extends from the front to the rear. The stepped section 73B is connected to the rear end of the tubular section 73A and is smaller in diameter than the tubular section 73A. The rear end surface 73C is an annular surface connected to the rear end of the stepped section 73B and intersecting the axis of rotation AX perpendicularly. A circular opening section 73D, open about the axis of rotation AX, is formed on the rear end surface section 73C. The spindle shaft section 60A of the spindle 60 extends through the opening section 73D from the rear to the front (Fig. 3). Retaining grooves 73E, which axially guide the balls 78D, are formed on the inner surface of the tubular section 73A of the outer hammer 73. Each retaining groove 73E has a groove shape that extends in the axial direction of the axis of rotation AX. A plurality of retaining grooves 73E are provided at intervals in the circumferential direction of the inner surface of the tubular section 73A. The plurality of balls 78D are arranged between the recessed areas 78C of the inner hammer 78 and the retaining grooves 73E of the outer hammer 73, respectively, and transmit the rotational force of the inner hammer 78 to the outer hammer 73. The inner hammer 78 and the outer hammer 73 are movable relative to each other in the axial direction along the axis of rotation AX. The inner hammer 78 moves axially relative to the outer hammer 73 while being guided by the retaining grooves 73E of the outer hammer 73 over the balls 78D. The inner hammer 78 and the outer hammer 73 are fixed relative to each other in the direction of rotation about the axis of rotation AX by the plurality of balls 78D. When the rotational force from the spindle 60 is transmitted to the inner hammer 78, the plurality of balls 78D transmits the rotational force of the inner hammer 78 to the outer hammer. The inner hammer 78 and the outer hammer 73 rotate together, with the axis of rotation AX serving as one axis of rotation for this purpose. In other words, the inner hammer 78 and the outer hammer 73 are movable relative to each other in the axial direction of the axis of rotation AX, but are fixed relative to each other in the direction of rotation about the axis of rotation AX. As described below, the inner hammer 78 moves in the axial direction of the axis of rotation AX when the striking tool 1 is driven. Therefore, the inner hammer 78 generates an oscillation in the axial direction of the axis of rotation AX when the striking tool 1 is driven.However, the outer hammer 73 is fixed relative to the hammer housing 4 and is movable relative to the inner hammer 78 in the axial direction of the axis of rotation AX. Therefore, even if the inner hammer 78 oscillates in the axial direction of the axis of rotation AX, the outer hammer 73 does not oscillate in the axial direction of the axis of rotation AX. Consequently, the outer hammer 73 can increase its moment of inertia in the direction of rotation about the axis of rotation AX to increase the impact force of the striking mechanism 70 without increasing the oscillation in the axial direction about the axis of rotation AX. The spiral retaining ring 71 and the bracket 72 are arranged between the internal gear 59 and the outer hammer 73. The spiral retaining ring 71 is located on the front face of the internal gear 59. It is fixed immovably in the forward-backward direction by being clamped to the inner wall of the hammer housing 4 under an outward preload. The inner diameter of the spiral retaining ring 71 is smaller than the outer diameter of the internal gear 59. Therefore, the spiral retaining ring 71 restricts the forward movement of the internal gear 59. The holder 72 is located on the front side of the spiral retaining ring 71. The inner diameter of the spiral retaining ring 71 is smaller than the outer diameter of the holder 72. Therefore, the spiral retaining ring 71 restricts backward movement of the holder 72. A plurality of balls 73F are arranged between the flange region 60B of the spindle 60 and the rear end surface region 73C of the outer hammer 73. A circular groove region, which movably holds the balls 73F, is formed on the rear end surface region 73C. The balls 73F support rotation of the outer hammer 73 relative to the spindle 60. A plurality of spheres 73G are arranged between the stepped section 73B of the outer hammer 73 and the bracket 72. The stepped section 73B and the bracket 72 movably hold the plurality of spheres 73G. The spheres 73G support rotation of the outer hammer 73 relative to the bracket 72. The first coil spring 74, the second coil spring 75, the washer 76, and the bearing coil spring 77 are arranged between the front surface of the rear end surface region 73C of the outer hammer 73 and the inner hammer 78. The bearing coil spring 77 biases the second coil spring 75 rearward via the washer 76. The first coil spring 74 and the second coil spring 75 generate spring forces for moving the inner hammer 78 forward. The bearing coil spring 77 also has a spring force for moving the inner hammer 78 forward, but its primary purpose is to hold the second coil spring 75 under a predetermined spring force, thus preventing the second coil spring 75 from moving in the forward-backward direction. The spring constant of the first coil spring 74 is smaller than the spring constant of the second coil spring 75.The spring constant of the bearing helical spring 77 is smaller than the spring constant of the first helical spring 74. The spring constants in ascending order are those of the bearing helical spring 77, the first helical spring 74, and the second helical spring 75. The behavior of the first helical spring 74 and the second helical spring 75 will be described later. This is the configuration of the impact mechanism 70. The anvil 81 is located at the front of the striking mechanism 70. The anvil 81 is connected to the front end of the spindle 60. The anvil 81 rotates through the inner hammer 78, with the axis of rotation AX serving as its axis of rotation. Furthermore, the anvil 81 is struck by the inner hammer 78 in the direction of rotation. The anvil 81 is an output shaft of the striking tool 1, which transmits the rotational force of the motor 40 and the impact force of the striking mechanism 70 to the tool accessory. The anvil 81 has an anvil shaft section 81A and arm sections 81B. The anvil shaft section 81A has a rod-like shape that is elongated in the front-back direction. The central axis of the anvil shaft section 81A and the axis of rotation AX coincide. The arm sections 81B are a pair of projecting components that extend radially outward from the rear end of the anvil shaft section 81A. An accessory hole 81C is provided on the front end surface of the anvil 81. The accessory hole 81C is designed to extend rearward from the front end surface of the anvil shaft region 81A. The tool accessory is inserted into the accessory hole 81C. The cylindrical anvil projection region 81D, which extends from the front to the rear, is provided on the rear end surface of the anvil 81. The anvil projection region 81D is inserted into the distal end opening region 60D, which is provided on the spindle 60. An anvil bearing 84 and an anvil bearing 86, arranged in a front-to-back direction, are provided around the anvil shaft section 81A at the front of the anvil 81. The anvil 81 is rotatably mounted by the anvil bearing 84 and the anvil bearing 86. The axis of rotation of the anvil 81, the axis of rotation of the inner hammer 78, the axis of rotation of the spindle 60, and the axis of rotation AX of the motor 40 coincide. An O-ring 85 is arranged between the anvil bearing 84 and the spindle shaft section 60A. An O-ring 87 is arranged between the anvil bearing 86 and the spindle shaft section 60A. The anvil bearing 84 and the anvil bearing 86 are held inside the small tubular section 4C of the hammer housing 4. The hammer housing 4 supports the anvil 81 via the anvil bearing 84 and the anvil bearing 86. A spiral retaining ring 82 and a washer 83 are arranged on the front of the arm sections 81B. The spiral retaining ring 82 secures the washer 83 to the hammer housing 4 by being fixed to the inner wall of the hammer housing 4 under an outward preload. The spiral retaining ring 82 is arranged out of contact with the anvil 81. The washer 83 and the anvil 81 are in contact with each other. When the motor 40 is activated to rotate the anvil 81, the washer 83 rotates in response to the rotation of the anvil 81. An accessory holding mechanism 88 is arranged around the front region of the anvil 81. The accessory holding mechanism 88 holds the tool accessory that is inserted into the accessory hole 81C of the anvil 81. The tool accessory can be removably attached to the accessory holding mechanism 88. The accessory holding mechanism 88 is a known technology, and therefore its description is omitted here. Operation of impact tool The following describes the operation when the impact tool 1 is activated. This operation is described with reference to an example when the user performs screw tightening work. The tool accessory (a screwdriver bit) used for screw tightening is inserted by the user into the accessory hole 81C of the anvil 81. The tool accessory, inserted into the accessory hole 81C, is held by the accessory holding mechanism 88. The user then operates the forward / reverse rotation switch lever 27 such that the motor 40 rotates in the forward direction. The user operates the trigger lever 26 by pressing it with the grip area 22 in their hand. When the trigger lever 26 is pressed, electrical power is supplied from the battery pack 10 to the motor 40 to activate it. As a result of the motor 40's activation, the rotor shaft 45 of the rotor 44 rotates. When the rotor shaft 45 rotates, its torque is transmitted to the planetary gear mechanism 50. Specifically, the torque of the rotor shaft 45 rotates the drive gear 58 of the planetary gear mechanism 50. The drive gear 58 rotates in the same direction as the rotor shaft 45. The axis of the drive gear 58 is aligned with the support of the rear rotor bearing 32, which supports the rotor shaft 45, and the front rotor bearing 33, which supports the drive gear 58 itself. When the drive gear 58 rotates, the three planet gears 57 arranged around the drive gear 58 rotate on their own axes. As described above, the three planet gears 57 are supported by the carrier 55. The carrier 55 is fixed by the carrier fixing component 51 in such a way that it is prevented from rotating. Therefore, the planet gears 57 do not rotate, even though they are rotatable on their own axes. The axis of each planet gear 57 is aligned with the support of the gear shank pin 56, which is fixed to the carrier 55. The internal gear 59 rotates on its own axes due to the rotations of the three planetary gears 57. When viewed in the direction of the axis of rotation AX, the drive gear 58 and the internal gear 59 rotate in opposite directions. In other words, the rotor 44 of the motor 40 and the internal gear 59 rotate in opposite directions. The torque of the internal gear 59 is transmitted to the spindle 60, which is connected to the internal gear 59 via the splined connection. The rotational speed of the spindle 60 is lower than the rotational speed of the rotor 44. The internal gear 59 and the spindle 60 rotate in the same direction relative to each other. In other words, the rotor 44 of the motor 40 and the spindle 60 rotate in opposite directions. The rotational force of the spindle 60 is transmitted to the inner hammer 78 via the three balls 62, which are arranged between the three spindle grooves 61 and the three hammer grooves 79. The spindle 60 and the inner hammer 78 are biased away from each other by the first coil spring 74, the second coil spring 75, and the bearing coil spring 77. Therefore, the three balls 62 are initially located between the central spindle groove regions 61A of the spindle 60 and the central hammer groove regions 79A of the inner hammer 78 when the striking tool 1 is started. When the rotational force of the spindle 60 is transmitted to the inner hammer 78 via the three balls 62, the inner hammer 78 rotates. The rotational force of the inner hammer 78 is transmitted to the outer hammer 73 via the balls 78D. The outer hammer 73 rotates at a speed equal to that of the inner hammer 78. The inner hammer 78 transmits the rotational force to the arm sections 81B of the anvil 81 via the hammer projection sections 78B. In other words, the anvil 81 rotates with the hammer projection sections 78B and the arm sections 81B in contact with each other. When the spindle 60 rotates (in the forward direction), with the hammer projection sections 78B and the arm sections 81B in contact with each other, the anvil 81 rotates together with the inner hammer 78, the outer hammer 73, and the spindle 60. In this case, the anvil 81 rotates without the impact force applied to it by the inner hammer 78 from the outer hammer 73, and the screw tightening operation progresses. A process in which the progress of the screw tightening work leads to an increase in the load acting on the anvil 81 and generates the impact force applied to the anvil 81 will now be described. First, the functions of the first helical spring 74, the second helical spring 75, and the bearing helical spring 77 are described. The preload forces of these helical springs influence the impact force applied by the inner hammer 78 to the anvil 81. Since the spring constant of the bearing helical spring 77 is extremely small compared to the first helical spring 74 and the second helical spring 75, the impact force applied by the inner hammer 78 to the anvil 81 is essentially influenced by the first helical spring 74 and the second helical spring 75. The spring constant of the first helical spring 74 is smaller than the spring constant of the second helical spring 75. If a small load is applied to the anvil 81 during screw tightening, the preload force (the spring force) exerted by the first helical spring 74 is applied to the inner hammer 78. If a heavy load is applied to the anvil 81 during screw tightening, the preload forces (the spring forces) exerted by the first helical spring 74 and the second helical spring 75 are applied to the inner hammer 78. The following description details the operation of an anvil 81 when a striking force is applied, focusing on two consecutive examples. The first case describes operation when a load less than a predetermined value is applied to anvil 81. The second case describes operation when a load equal to or greater than the predetermined value is applied to anvil 81. The first case will now be described. In the case where a load smaller than the predetermined value is applied to the anvil 81 as the screw tightening work progresses, the anvil 81, the inner hammer 78, and the outer hammer 73 stop rotating. When the spindle 60 rotates, and the inner hammer 78 and the outer hammer 73 stop rotating, the balls 62 move backward between the second spindle grooves 61C and the second hammer grooves 79C against the spring force of the first coil spring 74. The inner hammer 78 moves backward under a force exerted by the balls 62. This backward movement of the inner hammer 78 disengages the contact between the hammer projection areas 78B and the arm areas 81B. After moving backward, the inner hammer 78 moves forward while rotating under the spring force of the first coil spring 74. The outer hammer 73 rotates along with the inner hammer 78, although it does not move in the forward-backward direction. The anvil 81 is struck in the direction of rotation by the inner hammer 78. The anvil 81 is subjected to the rotational force about the axis of rotation AX and the impact force in the direction of rotation. The inner hammer 78, which strikes the anvil 81, moves backward while rotating in the reverse direction due to the impact. The backward movement of the inner hammer 78 causes the contact between the hammer projection areas 78B and the arm areas 81B to disengage. Then, while rotating, the inner hammer 78 moves forward again under the preload of the first coil spring 74 and strikes the anvil 81. Due to the sequence of events, the striking tool 1 can successively apply the impact force and the rotational force to the screw. The second case will now be described. In the case where a load equal to or greater than the predetermined value is applied to the anvil 81 as the screw tightening progresses, the inner hammer 78 initially behaves similarly to the first case. As the load applied to the anvil 81 increases, the impact force delivered to the inner hammer 78 after the anvil 81 has been struck also increases. The anvil 81 rotates backward and moves rearward with a greater range of motion than in the first case. Thus, the inner hammer 78 is subjected to the spring force of the second coil spring 75 in addition to the spring force of the first coil spring 74. As it rotates, the inner hammer 78 moves forward under the spring forces of the first coil spring 74 and the second coil spring 75, striking the anvil 81.Due to the sequence of events, the impact tool 1 can apply a stronger impact force and rotational force to the screws than in the first case. The impact tool 1 can initiate the impact action while employing a soft spring (the first coil spring 74) at the point of low load immediately after the screw tightening process begins. As the load increases, a stiffer spring (the second coil spring 75) is added to the impact action, allowing the screw to be tightened further. This is the operation of the impact tool 1. In the manner described above, the planetary gear mechanism 50 of the impact tool 1, according to the present embodiment, is configured to operate in star-type mode, with the carrier 55 fixed in a non-rotatable manner. When the planetary gear mechanism 50 operates in star-type mode, the motor 40, the internal gear 59, and the spindle 60 rotate in opposite directions. Consequently, the present embodiment allows the moment of inertia due to the rotation of the motor 40 and the moments of inertia due to the rotations of the internal gear 59 and the spindle 60 to cancel each other out, thus successfully suppressing the phenomenon of undesirable vibration of the main body of the impact tool 1 due to the moments of inertia at the start of operation and when the impact tool 1 stops.Therefore, the present embodiment can reduce the strain on the user when working with the impact tool 1, thereby improving the user-friendliness of the impact tool 1. In the impact tool 1 according to the present embodiment, the carrier 55 is fixed to the hammer housing 4 via the carrier fixing component 51 in a non-rotatable manner. Therefore, the carrier 55 can be securely fixed, thus preventing rotation of the planetary gears 57, which are subject to a strong rotational force from the motor 40 (the drive gear 58). Consequently, the rotational force of the drive gear 58 can be transmitted to the internal gear 59 without being attenuated by the planetary gears 57 and the carrier 55. If the carrier 55 were loosely fixed, the rotational force from the drive gear 58 would be unintentionally dampened by the planetary gears 57, and the rotational force transmitted to the internal gear 59 would likewise be undesirably attenuated.On the other hand, the present embodiment fixes the carrier 55 to the hammer housing 4 via the carrier fixing component 51, thereby enabling it to efficiently transmit the rotational force of the drive gear 58 to the internal gear 59. The striking tool 1 according to the present embodiment has an inner hammer 78, which is arranged around the spindle 60 and is rotatable in the same direction as the spindle 60 due to the rotational force of the spindle 60. Furthermore, the striking tool 1 has an anvil 81, which is arranged at least partially at the front with respect to the spindle 60 and is configured to be struck in the direction of rotation by the inner hammer 78. Therefore, the present embodiment allows the moment of inertia due to the rotation of the motor 40 and the moment of inertia due to the rotation of the inner hammer 78 to cancel each other out, thereby successfully suppressing the phenomenon of the main body of the striking tool 1 being undesirably shaken due to the moments of inertia at the start of operation of the electric tool 1 and at the time of stopping the striking tool 1.Therefore, the present embodiment can reduce the strain on the user when working with the impact tool 1, thereby improving the user-friendliness of the impact tool 1. In the present embodiment, the internal gear 59 and the spindle 60 are configured as separate, individual components. Therefore, this embodiment simplifies manufacturing compared to a configuration where the internal gear 59 and the spindle 60 are manufactured as a single, integrated component. Furthermore, this embodiment facilitates the use of different materials for these components compared to a configuration where the internal gear 59 and the spindle 60 are designed as a single, integrated component. In the present embodiment, the internal gear 59 and the spindle 60 are connected so as to be relatively movable in the axial direction of the axis of rotation of the internal gear 59 and the spindle 60. Therefore, the present embodiment can suppress the transmission of the vibration generated in the axial direction of the axis of rotation from the spindle 60 to the internal gear 59 when the impact tool 1 is driven. Consequently, the durability of the planetary gear mechanism 50 can be improved. In the present embodiment, the internal gear 59 and the spindle 60 are connected via the splined connection, which extends in the axial direction of the axis of rotation of the internal gear 59 and the spindle 60. Therefore, the present embodiment can achieve a structure that is excellent in its ability to transmit the power exerted in the direction of rotation from the internal gear 59 to the spindle 60 and in its self-aligning capability, while suppressing the transmission of the vibration generated in the axial direction of the axis of rotation from the spindle 60 to the internal gear 59 when the impact tool 1 is driven. In the present embodiment, the carrier fixing component 51 has a gear-shaped first engagement area 51B with a plurality of teeth that are formed circumferentially around the drive gear 58. Furthermore, the hammer housing 4 has a second engagement area 4B that is fitted to the first engagement area 51B. Therefore, the carrier fixing component 51 is fixed to the hammer housing 4 due to its circumferential gear shape, and this facilitates the housing's absorption of the force from the carrier 55 in the direction of rotation. Consequently, the carrier 55 can be securely fixed indirectly to the hammer housing 4. In the present embodiment, the support 55 is a metal component. The support fixing component 51 is a resin component. Therefore, while the strength of the support 55, to which the force from the planetary gears 57 is transmitted, can be improved by designing it as a metal component, the weight of the support fixing component 51 can be reduced by designing it as a resin component. Advantageous effects of the present embodiment are now described in comparison to an electric tool in which the planetary gear mechanism is used in a planetary-like operating mode. In the electric tool with the planetary gear mechanism used in the planetary-like operating mode, the carrier and the spindle can be designed as an integrated component. Designing the carrier and the spindle as an integrated component, for example, means that they must be manufactured by machining a metal material, which requires considerable labor. Furthermore, the electric tool structured in this way requires the design of a hollow-structured gear chamber to accommodate the planetary gears between the carrier and the spindle, thus complicating the structure. This leads to a further increase in the labor required for manufacturing. On the other hand, according to the present embodiment, the impact tool 1 allows the internal gear 59 and the spindle 60 to be designed separately as distinct individual components, thus simplifying manufacturing. Furthermore, unlike conventional electric tools, a hollow-structured gear chamber for accommodating the planetary gears is not required. The present embodiment allows the internal gear itself to be used as the gear chamber for accommodating the planetary gears, thereby simplifying the structure and reducing costs. According to the present embodiment, the internal gear 59 is largely open at its rear, making it easy to manufacture.When the impact tool 1 is assembled, the present embodiment allows the planetary gears to be mounted by simply placing them from the rear of the internal gear and supporting them through the gear shaft pins 56, thus simplifying the assembly of the impact tool 1. The present embodiment can achieve a reduction in manufacturing costs. Furthermore, according to the present embodiment, the impact tool 1 eliminates the need for a bearing to align the axis of the spindle 60. Therefore, the present embodiment can reduce the number of parts required to manufacture the impact tool 1, thereby simplifying the structure and reducing costs. B. Second embodiment A striking tool 1a according to a second embodiment is described. Fig. 9 is a drawing that schematically illustrates the configuration of the striking tool 1a. One difference between the striking tool 1a and the striking tool 1 is the positional relationship between the axis of rotation of the motor 40 and the axis of rotation of the spindle 60. Hereinafter, the axis of rotation of the motor 40 is referred to as the axis of rotation MAX. The axis of rotation of the spindle 60 is referred to as the axis of rotation SAX. In the striking tool 1 according to the first embodiment, the axis of rotation MAX of the motor 40 and the axis of rotation SAX of the spindle 60 lie on the same straight line. On the other hand, in the striking tool 1a according to the second embodiment, the axis of rotation MAX of the motor 40 and the axis of rotation SAX of the spindle 60 extend parallel to each other.In the present description, the same reference numerals as in the first embodiment are used to indicate mechanisms and components provided in the impact tool 1a according to the second embodiment, that they have the same configuration and function as the mechanisms and components provided in the impact tool 1 according to the first embodiment. As shown in Fig. 9, the impact tool 1a comprises the motor 40, the planetary gear mechanism 50, the spindle 60, the impact mechanism 70, a first gear shaft 91, and a second gear shaft 92. The planetary gear mechanism 50 according to the second embodiment is configured to operate as a star gear, similar to the first embodiment. In other words, the drive gear 58 is rotatable. The planet gears 57 can rotate on their own axes. The carrier 55, which supports the planet gears 57, is fixed against rotation by the carrier fixing element 51. Because the carrier 55, which supports the planet gears 57, is fixed against rotation, the planet gears 57 cannot rotate around the drive gear 58, although they are rotatable on their own axes. The internal gear 59 is rotatable.The planetary gear mechanism 50 is configured similarly to the first embodiment described above, and therefore a detailed description of it is omitted here. The first transmission shaft 91 is fitted onto the opening area 59B provided on the internal gear 59. The first transmission shaft 91 has a shaft section 91A, a gear section 91B, and a connecting section 91C. The connecting section 91C is located at the rear end of the shaft section 91A and has a splined connection formed on it. The connecting section 91C provided on the internal gear 59 and the connecting section 91C provided on the first transmission shaft 91 are connected by a splined connection extending in the axial direction of the axis of rotation MAX.Therefore, the present embodiment can achieve a structure that excels in its ability to transmit the power exerted in the direction of rotation from the internal gear 59 to the first gear shaft 91 and in its self-aligning capability, while suppressing the transmission of the vibration generated in the axial direction of the axis of rotation MAX from the first gear shaft 91 to the internal gear 59 when the impact tool 1a is driven. The first gear shaft 91 rotates in the same direction as the direction of rotation of the internal gear 59. In other words, the first gear shaft 91 rotates in the opposite direction to the direction of rotation of the rotor shaft 45. The first transmission shaft 91 transmits a rotational force to the second transmission shaft 92. The second transmission shaft 92 has a shaft section 92A, a front-end gear section 92B, and a rear-end gear section 92C. The gear section 91B of the first transmission shaft 91 is located at the front end of the shaft section 91A and has a gear formed thereon. The gear section 91B of the first transmission shaft 91 meshes with the rear-end gear section 92C of the second transmission shaft 92. The first transmission shaft 91 transmits the rotational force to the second transmission shaft 92 via the gear section 91B and the rear-end gear section 92C. The first transmission shaft 91 and the second transmission shaft 92 rotate in opposite directions. The second transmission shaft 92 is connected to the spindle 60. The front-end gear section 92B, provided on the second transmission shaft 92, meshes with a spindle gear section 60E, also provided on the spindle 60. A torque from the second transmission shaft 92 is transmitted to the spindle 60 via the front-end gear section 92B and the spindle gear section 60E. The spindle 60 rotates in the opposite direction to the direction of rotation of the second transmission shaft 92. In other words, the spindle 60 rotates in the opposite direction to the direction of rotation of the rotor shaft 45 (the motor 40). The spindle 60 rotates in the same direction as the internal gear 59 and the first transmission shaft 91. The rotational force of the spindle 60 is transmitted to the impact mechanism 70, the anvil 81 and the tool accessories in the same way as in the first embodiment, and therefore a description of the same is omitted here. In the manner described above, the impact tool 1, according to the present embodiment, has the planetary gear mechanism 50 configured to operate in star mode, with the carrier 55 fixed in a non-rotatable manner. When the planetary gear mechanism 50 operates in star mode, the motor 40 and the internal gear 59 rotate in opposite directions. Furthermore, in impact tool 1a, the rotational force of the internal gear 59 is transmitted to the spindle 60 via the first gear shaft 91 and the second gear shaft 92. Consequently, in impact tool 1a, the motor 40, the internal gear 59, and the spindle 60 also rotate in opposite directions, similar to the first embodiment.Accordingly, the present embodiment allows the moment of inertia due to the rotation of the motor 40 and the moments of inertia due to the rotations of the internal gear 59 and the spindle 60 to cancel each other out, thereby successfully suppressing the phenomenon of undesirable vibration of the main body of the impact tool 1a due to the moments of inertia at the start of operation and when the impact tool 1a stops. Consequently, the present embodiment can reduce the strain on the user when working with the impact tool 1a. The present embodiment can improve the user-friendliness of the impact tool 1a. The striking tool 1a according to the second embodiment has an inner hammer 78 arranged around the spindle 60 and rotatable in the same direction as the spindle 60 due to the spindle's rotational force, similar to the first embodiment described above. Furthermore, the striking tool 1a has an anvil 81, arranged at least partially at the front face with respect to the spindle 60 and configured to be struck by the inner hammer 78 in the direction of rotation. Therefore, the present embodiment allows the moment of inertia due to the rotation of the motor 40 and the moment of inertia due to the rotation of the inner hammer 78 to cancel each other out, thus successfully suppressing the phenomenon of the main body of the striking tool 1a being undesirably shaken due to the moments of inertia at the start of operation and at the time the striking tool 1a stops.Therefore, the present embodiment can reduce the strain on the user when working with the impact tool 1a. The present embodiment can improve the user-friendliness of the impact tool 1a. In the impact tool 1a according to the second embodiment, the internal gear 59 and the spindle 60 are configured as separate, individual components, similar to the first embodiment described above. Therefore, the present embodiment can simplify manufacturing compared to a configuration in which the internal gear 59 and the spindle 60 are manufactured as an integrated component. Furthermore, the present embodiment facilitates the use of different materials for these components compared to a configuration in which the internal gear 59 and the spindle 60 are designed as an integrated component. Apart from this, the impact tool 1a according to the second embodiment exhibits similar advantages to the impact tool 1 according to the first embodiment described above. The corresponding relationship between each component (feature) in the embodiments described above and each component (feature) of the present disclosure or invention is described below. However, each component in the embodiments is merely an example and is not intended to limit any component of the present disclosure or invention. The striking tool 1 and the striking tool 1a are each an example of an "electric tool". The motor 40 is an example of a "motor". The spindle 60 is an example of a "spindle". The planetary gear mechanism 50 is an example of a "planetary gear mechanism". The drive gear 58 is an example of a "sun gear". The planet gear 57 is an example of a "planetary gear". The internal gear 59 is an example of an "internal gear". The support 55 is an example of a "support". The support fixing component 51 is an example of a "support fixing component". The hammer housing 4 is an example of a "housing". The splined connection formed at the joint 59C and the joint 60C is an example of a "splined connection". The first engagement area 51B is an example of a "first engagement area". The second intervention area 4B is an example of a “second intervention area”.The inner hammer 78 is an example of a "hammer". The anvil 81 is an example of an "anvil". The embodiments described above serve only as examples, and the electric tool according to the present disclosure is not limited to the striking tool 1 and striking tool 1a shown by way of example. For instance, non-restrictive modifications may be added, which are listed below by way of example. In addition, at least one of these modifications may be used in combination with one of the striking tool 1 and striking tool 1a shown by way of example in one of the embodiments and in the claims. For example, the term "electric tool" is not limited to impact tools, and various electric tools can be used as long as the electric tool is configured so that the motor's axis of rotation and the spindle's axis of rotation are parallel to each other or on the same straight line, such as a screwdriver or a drill. Furthermore, various electric tools can be used as impact tools as long as the electric tool delivers an impact in a rotational direction, such as an impact wrench or an impact driver. The support 55 does not need to be fixed by the support fixing component 51, as long as it is not rotatably fixed. For example, the support 55 itself can be designed in such a way that it can be fixed to an external housing. The internal gear 59 and the spindle 60 do not need to be configured as separate, individual components. A configuration that integrates the internal gear 59 and the spindle 60 as a single component can be used. For example, the internal gear 59 and the spindle 60 can be manufactured as a single component by machining a single metal material. The stiffness of the internal gear 59 and the spindle 60 can be improved. The connection between the internal gear 59 and the spindle 60 is not limited to splined connection. Other configurations can be used, provided that the internal gear 59 and the spindle 60 are connected in a way that allows them to move relatively freely in the axial direction of their axis of rotation. Examples of applicable connections include one using a keyway and another using a hexagonal projection and recessed areas. The support fixing component 51 is not limited to being made of a synthetic resin material. The support fixing component 51 can be made of a metal component. It is explicitly emphasized that all features disclosed in the description and / or the claims are to be considered separate and independent of one another for the purposes of the original disclosure as well as for the purpose of limiting the claimed invention, irrespective of the combinations of features in the embodiments and / or the claims. It is explicitly stated that all range specifications or specifications of groups of units disclose every possible intermediate value or subgroup of units for the purposes of the original disclosure as well as for the purpose of limiting the claimed invention, in particular also as a boundary of a range specification. REFERENCE MARK LIST 1, 1a: Impact tool, 2: Main body housing, 2S: Screw, 3: Rear cover, 4: Hammer housing, 4B: Second engagement area, 4C: Small tubular area, 10: Battery pack, 21: Motor mounting area, 22: Handle area, 23: Battery holding area, 24: Intake opening, 25: Exhaust opening, 26: Trigger lever, 27: Forward / reverse / rotary shift lever, 28: Battery mounting area, 29: Control, 31: Fan wheel, 32: Rear rotor bearing, 33: Front rotor bearing, 40: Motor, 41: Stator, 42: Stator core, 43: Coil, 44: Rotor, 45: Rotor shaft, 46: Rotor core, 47: Rotor magnet, 48: Sensor magnet, 49: Sensor board, 50: Planetary gear mechanism, 51: Carrier fixing component, 51A: Holding area, 51B: First engagement area, 53: O-ring, 55: Carrier, 55A: Opening area, 55B: Bearing fixing area, 56: Gear shaft pin, 57: Planet gear, 58: Drive gear, 59: Internal gear, 59A: Inner wall, 59B: Opening area, 59C: Connection area, 60: Spindle, 60A: Spindle shaft area,60B: Flange area, 60C: Connection area, 60D: Distal end opening area, 60E: Spindle gear area, 61: Spindle groove, 61A: Middle spindle groove area, 61B: First spindle groove area, 61C: Second spindle groove area, 62: Ball, 70: Striking mechanism, 71: Spiral retaining ring, 72: Bracket, 73: Outer hammer, 73A: Tubular area, 73B: Stepped area, 73C: Rear end surface area, 73D: Opening area, 73E: Retaining groove, 73F: Ball, 73G: Ball, 74: First coil spring, 75: Second coil spring, 76: Washer, 77: Bearing coil spring, 78: Inner hammer, 78A: Hammer main body area, 78B: Hammer projection area, 78C: Excluded area, 78D: Ball, 79: Hammer groove, 79A: Middle hammer groove area, 79B: First hammer groove area, 79C: Second hammer groove area, 81: Anvil, 81A: Anvil shaft area, 81B: Arm area, 81C: Accessory hole, 81D: Anvil projection area, 82: Spiral retaining ring, 83: Washer, 84: Anvil bearing, 85: O-ring, 86: Anvil bearing,87: O-ring, 88: Accessory retaining mechanism, 91: First transmission shaft, 91A: Shaft area, 91B: Gear area, 91C: Connecting area, 92C: Second transmission shaft, 92A: Shaft area, 92B: Front end gear area, 92C: Rear end gear area, AX: Axis of rotation, MAX: Axis of rotation, SAX: Axis of rotation QUOTES INCLUDED IN THE DESCRIPTION This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature JP 4 457 170 B1

[0002]

Claims

An electric tool comprising a motor, a spindle configured to rotate due to a torque transmitted by the motor, a planetary gear mechanism configured to transmit the torque of the motor to the spindle, and a housing accommodating at least part of the planetary gear mechanism, wherein an axis of rotation of the motor and an axis of rotation of the spindle are arranged on the same straight line, and wherein the planetary gear mechanism comprises a sun gear into which the torque of the motor is input, a plurality of planet gears arranged on a radial outer side about an axis of rotation of the sun gear, a support which is provided to be non-rotatable relative to the housing and is configured to support the multiple planet gears such that they are rotatable on their own axes, and an internal gear.which is rotatably arranged on the radial outer side of the majority of planetary gears and is configured to transmit the rotational force to the spindle. Electric tool according to claim 1, further comprising a carrier fixing component configured to fix the carrier non-rotatably to the housing. Electric tool according to claim 1 or 2, wherein the internal gear and the spindle are configured as separate individual components. Electric tool according to one of claims 1 to 3, wherein the internal gear and the spindle are connected in a relatively movable manner in an axial direction of a rotational axis of the internal gear and the spindle. Electric tool according to one of claims 1 to 4, wherein the internal gear and the spindle are connected via a splined connection extending in the axial direction of the axis of rotation of the internal gear and the spindle. Electric tool according to claim 2 or according to one of claims 3 to 5 according to claim 2, wherein the carrier fixing component has a gear-shaped first engagement area on which a plurality of teeth are formed circumferentially around the axis of rotation of the sun gear, and wherein the housing has a second engagement area which is compatible with the first engagement area. Electric tool according to claim 2 or one of claims 3 to 6 according to claim 2, wherein the support is a metal component, and wherein the support fixing component is a synthetic resin component. Electric tool according to any one of claims 1 to 7, further comprising a hammer arranged around the spindle and rotatable in the same direction as the spindle due to a rotational force of the spindle, and an anvil arranged at least partially on a front side in relation to the spindle and configured to be struck by the hammer in a rotational direction. An electric tool comprising a motor and a spindle configured to rotate by means of a rotational force transmitted by the motor, wherein an axis of rotation of the motor and an axis of rotation of the spindle are arranged parallel to each other or on the same straight line, and wherein the motor and the spindle rotate in opposite directions to each other. Electric tool according to claim 9, further comprising a planetary gear mechanism configured to transmit the torque from the motor to the spindle, wherein the planetary gear mechanism comprises a sun gear, a planet gear, a carrier which mounts the planet gear in such a way that it is rotatable on its own axis, and an internal gear, wherein the torque of the motor is input into the sun gear, wherein the carrier is fixed in a non-rotatable manner, wherein the internal gear is rotatable, and wherein a torque of the internal gear is output to the spindle.

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