Aviation sheet metal rivet hammer

Abstract

The utility model discloses an aviation sheet metal rivet hammer, and belongs to the field of aviation sheet metal tools. The aviation sheet metal rivet hammer comprises a hammer body and a hammer handle, wherein the hammer body is vertically arranged at one end of the hammer handle. A motor, a gear assembly and a battery pack are installed in a cavity of the hammer handle. The hammer body comprises a hammer head, an air cylinder body and a piston. A gas containing cavity and a piston cavity which are communicated are formed in the air cylinder body, nitrogen is contained in the gas containing cavity, a piston is slidably installed in the piston cavity, and a hammer is slidably installed at the lower end of the piston cavity. The motor drives disc teeth in the gear assembly to rotate and drives semicircular teeth to rotate, so that the piston is driven to move axially, and nitrogen in the gas containing cavity is compressed. When the semicircular teeth are separated from the spur rack of the piston, the compressed nitrogen generates impact force on the piston, the piston reversely impacts the hammer head, and the knocking effect is achieved. The problems that an existing automatic punching device for the rivet head of the aviation metal plate needs to be externally connected with a pipeline, so that operation in a narrow space is inconvenient, hand hammering operation is strenuous, and efficiency is low are solved.

Description

Technical Field

[0001] The invention belongs to the field of aviation sheet metal tools, and in particular relates to an aviation sheet metal rivet hammer. Background Art

[0002] At present, the equipment used for stamping rivet heads of aviation sheet metal is mainly pneumatic rivet guns or hydraulic butt-crushing pliers. When using them, it is necessary to pull the air supply pipe or hydraulic pipe to provide power for them. It is not convenient to operate in the narrow space inside the wing or fuselage, and the work efficiency is low.

[0003] A hand hammer is relatively flexible and is used to punch rivet heads in a narrow space. During operation, the human hand holds the hammer and swings it. Long-term operation will overdraw the strength of the arm and reduce work efficiency. Summary of the invention

[0004] Technical problem to be solved: In order to avoid the deficiencies of the prior art, the present invention provides an aviation sheet metal rivet hammer, which is an electric rivet hammer, which solves the problems that the existing aviation sheet metal rivet head automatic stamping equipment requires external pipelines, resulting in inconvenience in operation in a small space, and the hand hammer is laborious and inefficient to operate.

[0005] The technical solution of the present invention is: an aviation sheet metal rivet hammer, comprising a hammer body and a hammer handle, wherein the hammer body is vertically mounted at one end of the hammer handle;

[0006] The hammer handle has a cavity structure, in which a motor, a gear assembly, and a battery pack are installed; the motor is coaxial with the hammer handle, and the end of the motor output shaft is meshed with the gear assembly; the gear assembly is used to drive the piston in the hammer body to reciprocate; the battery pack supplies power to the motor;

[0007] The hammer body comprises a hammer head, a cylinder body and a piston; a stepped cavity is provided inside the cylinder body along its axis, one end of the cavity of the cylinder body is an air-containing cavity, and the other end is a piston cavity; nitrogen is filled in the air-containing cavity, and a piston is slidably installed in the piston cavity; an opening is provided in the side wall of the cylinder body through the piston cavity, the edge of the opening is fixedly connected to the end of the hammer handle and connected to the cavity of the hammer handle; a spur rack is axially provided on the outer wall of the piston facing the opening for meshing with the gear assembly; a guide hole penetrating the piston cavity is provided along the axis at one end of the cylinder body away from the air-containing cavity, the hammer head is coaxially installed at the end of the cylinder body, the mounting part of the hammer head is axially limited and slidably installed in the guide hole, and the end of the mounting part extends into the piston cavity.

[0008] A further technical solution of the present invention is: the gear assembly includes disc teeth and semicircular teeth, the disc teeth are rotatably installed in the hammer handle through bearings, and their installation axis is perpendicular to the motor output shaft; the end of the motor output shaft is a gear structure, which is engaged with the disc teeth and is used to drive the disc teeth to rotate; the semicircular teeth are coaxially fixedly connected with the disc teeth, the overall axial cross-section of the semicircular teeth is semicircular, and a tooth profile is provided on the outer diameter of the semicircle, and the semicircular teeth are engaged with the spur rack of the piston.

[0009] A further technical solution of the present invention is that the disc teeth and the semicircular teeth are matched with threaded holes next to the mounting shaft holes at their centers, the two are coaxially superimposed, and are fixedly connected by screws passing through the threaded holes.

[0010] A further technical solution of the present invention is: the hammer head includes a guide rod and a hammering part; the guide rod serves as the mounting part of the hammer head, and the guide rod is a cylindrical rod as a whole, which is coaxially fixed to one side of the hammering part; the side of the hammering part facing away from the guide rod is the striking surface of the hammer head.

[0011] A further technical solution of the present invention is: the hammer head is axially limited by a limiting assembly, and the limiting assembly includes a ball, a spring, and a screw; the hammer head mounting end of the cylinder body is provided with a limiting hole that vertically passes through the guide hole, and the limiting hole is a threaded hole; the screw is inserted into the limiting hole, and the two are threadedly connected; the spring is sleeved on the smooth rod part at the end of the screw, one end of the spring is against the threaded part of the screw, and the other end is fixed with a ball; a sliding groove is axially provided on the outer diameter of the guide rod, and the ball is elastically pressed into the sliding groove.

[0012] A further technical solution of the present invention is: the hammer body also includes a hammer angle, and the hammer angle includes a connecting part and a nail pulling part; the connecting part is cover-shaped and threadedly connected to an end of the cylinder body away from the hammer head; the nail pulling part is a scissors-shaped structure, fixedly arranged on the outer end surface of the connecting part, and used for pulling nails.

[0013] A further technical solution of the present invention is: a piston ring is sleeved on the outer wall of the piston near one end of the air chamber. The piston ring is made of rubber and plays a sealing role to increase the compression ratio of nitrogen in the air chamber when the piston moves.

[0014] A further technical solution of the present invention is that: the side wall of the cylinder body is provided with a through hole connected to the air containing cavity, which is used to fill the air containing cavity with nitrogen.

[0015] A further technical solution of the present invention is: a control switch is provided in the middle of the hammer handle for controlling the action of the motor.

[0016] Beneficial Effects

[0017] The beneficial effect of the present invention is that: the aviation sheet metal rivet hammer described in the present invention uses a battery pack to power the motor, and the motor drives the disc teeth in the gear assembly to rotate, thereby driving the semicircular teeth to rotate, and the rotation of the semicircular teeth drives the piston to move axially, compressing the nitrogen in the air chamber. When the semicircular teeth and the spur rack on the piston are disengaged, the compressed nitrogen at this time obtains high-pressure compression potential energy, generating an impact force on the piston, and the piston reversely impacts the hammer head, causing the hammer head to do work and achieve a knocking effect.

[0018] The structure of the present invention has no external circuits and pipelines, is flexible to use, and can operate in a narrow space inside a wing or fuselage. The hammer angle is detachable to adapt to a smaller space. At the same time, the motor drives the piston to do work on the compressed nitrogen. Nitrogen is a stable inert gas with the characteristics of large compressed elastic potential energy and low energy loss. When the spur rack on the piston is disengaged, it can impact the hammer head under the action of sufficiently large potential energy of the compressed nitrogen, achieving a good knocking effect. The structural design of the semicircular teeth and their linkage design with the disc teeth and spur racks realize the reciprocating motion of the piston, and the reliability of power transmission is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a perspective schematic diagram of the overall structure of the present invention;

[0020] Figure 2 It is an exploded schematic diagram of the overall structure of the present invention;

[0021] Figure 3 It is a schematic cross-sectional view of the hammer body in the present invention;

[0022] Figure 4 It is a schematic diagram of the cylinder structure of the present invention;

[0023] Figure 5 It is a schematic diagram of the disc tooth structure in the present invention;

[0024] Figure 6 It is a schematic diagram of the semicircular gear structure in the present invention;

[0025] Figure 7 This is a schematic diagram of the structure of the end portion of the motor output shaft in the present invention;

[0026] Figure 8 This is a schematic diagram of the piston structure in the present invention;

[0027] Fig. 9 It is a schematic diagram of the hammer structure in the present invention;

[0028] Fig.10 It is a schematic diagram of the installation structure of the limit assembly in the present invention;

[0029] Fig.11 It is a schematic diagram of the initial meshing position of the semicircular teeth and the spur rack of the piston in the present invention;

[0030] Fig.12 It is a schematic diagram of the position where the semicircular teeth and the spur rack of the piston are disengaged in the present invention.

[0031] Description of reference numerals:

[0032] 1. hammer body, 11. hammer head, 111. guide rod, 112. hammering part, 113. slide groove, 12. cylinder body, 121. air chamber, 122. piston chamber, 123. opening, 124. guide hole, 125. limit hole, 126. through hole, 127. first external thread, 128. second external thread, 13. piston, 131. straight rack, 132. piston ring, 14. limit assembly, 141. ball, 142. spring, 143. screw, 15. hammer angle, 151. connecting part, 152. nail lifting part,

[0033] 2. Hammer handle, 21. Motor, 211. Motor output shaft, 22. Gear assembly, 221. Disc teeth, 2211. Disc teeth gear teeth, 2212. Disc teeth mounting shaft hole, 2213. Disc teeth threaded hole, 222. Semicircular teeth, 2221. Semicircular teeth gear teeth, 2222. Semicircular teeth mounting shaft hole, 2223. Disc teeth threaded hole, 223. Mounting shaft, 23. Battery pack, 24. Control switch. DETAILED DESCRIPTION

[0034] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0035] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0036] See also Figure 1-2 The present embodiment provides an aviation sheet metal rivet hammer, including a hammer body 1 and a hammer handle 2. The hammer body 1 is vertically mounted at one end of the hammer handle 2. The hammer handle 2 serves as a hand-held portion of the rivet hammer, and the hammer body 1 serves as a striking portion of the rivet hammer.

[0037] The hammer handle 2 is a cylindrical hollow shell structure, with the middle part thinner than the two ends, which is convenient for holding. A motor 21, a gear assembly 22, and a battery pack 23 are installed in the cavity of the hammer handle 2. Figure 1As shown, the motor 21 is coaxial with the hammer handle 2 and is installed in the cavity at the front end of the hammer handle 2. The output shaft end of the motor 21 is meshed with the gear assembly 22. The gear assembly 22 is rotatably installed in the cavity of the hammer handle 2 through the mounting shaft 223 and the bearing, and is used to drive the piston 13 in the hammer body 1 to reciprocate. The battery pack 23 is installed in the cavity at the rear end of the hammer handle 2, and is electrically connected to the motor 21 to supply power to the motor 21. A control switch 24 is provided in the middle of the hammer handle 2 for controlling the action of the motor 21. The control switch is connected in series in the connection circuit between the battery pack 23 and the motor 21.

[0038] See also Figure 5-7 The gear assembly 22 includes a disc tooth 221 and a semicircular tooth 222. The disc tooth 221 is rotatably mounted in the hammer handle 2 through a mounting shaft 223 and a bearing, and its mounting axis is perpendicular to the motor output shaft 211. The end of the motor output shaft 211 is a gear structure, which is meshed with the disc tooth 2211 of the disc tooth 221 facing the motor output shaft 211 and arranged around the disc tooth, and the disc tooth 221 is driven to rotate through the motor output shaft 211. The disc tooth 221 has the functions of reducing speed, increasing torque, and steering the motor output shaft 211. The semicircular tooth 222 is coaxially fixedly connected with the disc tooth 221, and is jointly mounted on the mounting shaft 223. The semicircular tooth 222 is located on the side of the disc tooth 221 facing away from the motor output shaft 211. The axial section of the semicircular tooth 222 is semicircular as a whole, and the semicircular outer diameter is provided with a semicircular tooth tooth 2221 for driving the piston 13. The disc tooth 221 is provided with two threaded holes 2213 beside the mounting shaft hole 2212 at the center thereof. Correspondingly, the semicircular tooth 222 is provided with two threaded holes 2223 matching the threaded hole 2213 of the disc tooth beside the mounting shaft hole 2222 at the center thereof. The disc tooth 221 and the semicircular tooth 222 are coaxially stacked so that the threaded holes of the two are aligned. The disc tooth 221 and the semicircular tooth 222 are fixedly connected by screws passing through the threaded holes and cooperating with nuts. When the disc tooth 221 rotates, the semicircular tooth 222 is driven to rotate at the same frequency. Due to the structural characteristics of the semicircular tooth 222, it works intermittently during the rotation process.

[0039] See also Figure 1-4 The hammer body 1 includes a hammer head 11, a cylinder body 12, a piston 13, and a hammer angle 15. The cylinder body 12 is the main part of the hammer body 1 and is used to install other components of the hammer body 1. Figure 3 , 4As shown, a stepped through cavity is provided inside the cylinder body 12 along its axis, the upper end of the cavity of the cylinder body 12 is an air chamber 121, and the lower end is a piston chamber 122. The air chamber 121 is filled with nitrogen, and a through hole 126 connected to the air chamber 121 is provided on the side wall of the cylinder body 12, which is used to fill the air chamber 121 with nitrogen. When not inflated, the through hole 126 needs to be closed. The piston 13 is slidably installed in the piston chamber 122, and an opening 123 is provided on the side wall of the cylinder body 12 through the piston chamber 122. The edge of the opening 123 is fixedly connected to the end of the hammer handle 2 and connected to the cavity of the hammer handle 2. Specifically, the opening 123 is cylindrical, and the outer diameter of its edge is provided with a second external thread 128, which cooperates with the internal thread matched with the front end of the hammer handle 2 to achieve a threaded fixed connection between the opening 123 and the hammer handle 2.

[0040] See also Figure 8 The main body of the piston 13 is a cylindrical structure. A spur rack 131 is axially arranged on the outer wall of the piston 13 facing the opening 123, which is used to mesh with the semicircular teeth 222 of the gear assembly 22. When the semicircular teeth 222 rotate clockwise, the gear teeth 2221 of the semicircular teeth mesh with the spur rack 131, thereby driving the piston 13 to move upward and compress the nitrogen in the air chamber 121. A piston ring 132 is sleeved on the outer wall of the piston 13 near one end of the air chamber 121. The piston ring 132 is made of rubber and plays a sealing role. It is used to increase the compression ratio of the nitrogen in the air chamber 121 when the piston 13 moves.

[0041] 3 and 4, the end of the cylinder body 12 away from the air chamber 121 is provided with a guide hole 124 penetrating the piston chamber 122 along the axis, and the hammer head 11 is coaxially mounted on the end of the cylinder body 12. Fig. 9 As shown, the hammer head 11 includes a guide rod 111 and a hammering part 112. The guide rod 111 is a cylindrical rod as a whole, and is coaxially fixed to one side of the hammering part 112. The side of the hammering part 112 facing away from the guide rod 111 is the striking surface of the hammer head 11. The guide rod 111 of the hammer head 11 is axially limited and slidably installed in the guide hole 124 through the limit assembly 14, and the upper end of the guide rod 111 extends into the piston cavity 122. The hammer head has a variety of structures, including a riveting hammer, an impact hammer, and a flat-headed hammer, which can be replaced according to usage requirements. The difference between a riveting hammer, an impact hammer, and a flat-headed hammer is that the structure of the hammering part 112 is different. Fig. 9 The structure of a riveting hammer is shown. The riveting hammer is used to rivet rivets of aviation sheet metal, and a concave hole is set in the middle of its striking surface. The impact hammer is used to withdraw the rivet head, and its hammering part 112 is a pointed shaft structure. The flat-headed hammer is used for striking, and the striking surface of its hammering part 112 is a flat structure, which is used to increase the striking area and ensure that the contact surface is evenly stressed.

[0042] See also Fig.10The hammer head 11 is axially limited by the limit assembly 14, and the limit assembly 14 includes a ball 141, a spring 142, and a screw 143. The hammer head mounting end of the cylinder body 12 is provided with a limit hole 125 that vertically penetrates the guide hole 124, and the limit hole 125 is a threaded hole. The screw 143 is inserted into the limit hole 125, and its threaded portion is threadedly connected with the limit hole 125. The spring 142 is sleeved on the smooth rod portion of the inner end of the screw 143, one end of the spring 142 is against the threaded portion of the screw 143, and the other end is fixed with a ball 141. Correspondingly, as Fig. 9 As shown, a slide groove 113 is axially arranged on the outer diameter of the guide rod 111, and the ball 141 matches the slide groove 113. The ball 141 is elastically pressed into the slide groove 113 under the push of the spring 142. The limit assembly 14 can limit the axial position of the hammer head 11 to prevent it from being separated from the cylinder body 12 during the striking process.

[0043] See also Figure 2 , Fig.11 The hammer angle 15 includes a connecting portion 151 and a nail removing portion 152. The connecting portion 151 is in the shape of a cover, and is threadedly connected to one end of the cylinder body 12 away from the hammer head 11. Specifically, a first external thread 127 is provided at the end of the cylinder body 12 away from the hammer head 11, and is fixedly connected to the internal thread correspondingly provided on the connecting portion 151. The nail removing portion 152 is a scissor-like structure, which is fixedly arranged on the outer end surface of the connecting portion 151 and is used for removing nails. When the rivet head needs to be removed, the nail removing portion 152 of the hammer angle 15 can clamp the rivet head, so that the overall rivet hammer is a lever structure, and the hammer handle 2 is pressed to remove the rivet. The structure of the hammer angle 15 can be set to a pointed head or a flat head, and the design can be matched according to different workpiece structures. At the same time, the hammer angle 15 can be removed to meet the needs of operations in too narrow a space.

[0044] Specific working principle: Fig.11 , 12 As shown, the motor 21 is connected in series with the control switch 24 and the battery pack 23 to form a control circuit for controlling the motor 21. The gear structure at the end of the output shaft 211 of the motor 21 is driven by the right-angle gear of the disc tooth 221, driving the disc tooth 221 to rotate clockwise, and then the power is synchronized to the semicircular tooth 222. The semicircular tooth 222 is meshed with the straight rack 131 that drives the piston 13, and then drives the piston 13 to move upward, compressing the nitrogen in the air chamber 121 of the cylinder body 12. Nitrogen is a stable inert gas with the characteristics of large compression elastic potential energy and low energy loss. After half a rotation, the semicircular tooth 222 is separated from the straight rack 131. The piston 13 is subjected to the potential energy of the compressed nitrogen and performs a recovery movement, which produces an impact downward, so that the lower end face of the piston 13 hits the guide rod 111 of the hammer head 11, so that the hammering part 112 hits the surface of the workpiece to achieve the effect of knocking. The above piston 13 moves upward to compress the nitrogen and moves downward to impact the hammer head 11. Repeated movement realizes the function of continuous knocking.

[0045] At the same time, in order to achieve overload protection in this embodiment, an overload protection device is connected in series in the control circuit of the motor 21. By setting a vibration sensor module in the hammer handle 2, when the impact energy of the piston 13 is not applied to the workpiece, or the impact energy is too large, the hammer handle 2 produces vibration beyond the specified range. At this time, the vibration sensor module is powered off, thereby playing a role in protecting against overload.

[0046] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. An aviation sheet metal rivet hammer, characterized by: It comprises a hammer body (1) and a hammer handle (2), wherein the hammer body (1) is vertically mounted on one end of the hammer handle (2); The hammer handle (2) has a hollow structure, in which a motor (21), a gear assembly (22), and a battery pack (23) are installed; the motor (21) is coaxial with the hammer handle (2), and the output shaft end of the motor (21) is meshed with the gear assembly (22); the gear assembly (22) is used to drive the piston (13) in the hammer body (1) to reciprocate; the battery pack (23) supplies power to the motor; The hammer body (1) comprises a hammer head (11), a cylinder body (12), and a piston (13); a stepped cavity is provided inside the cylinder body (12) along its axis, one end of the cavity of the cylinder body (12) is an air chamber (121), and the other end is a piston chamber (122); nitrogen is contained in the air chamber (121), and the piston (13) is slidably mounted in the piston chamber (122); an opening (123) is provided on the side wall of the cylinder body (12) through the piston chamber (122), and the edge of the opening (123) is fixedly connected to the end of the hammer handle (2). The piston (13) is connected to the air chamber (121) and is connected to the cavity of the hammer handle (2); a spur rack (131) is axially provided on the outer wall of the piston (13) facing the opening (123) for meshing with the gear assembly (22); a guide hole (124) is axially provided at one end of the cylinder body (12) away from the air chamber (121) and passes through the piston chamber (122); the hammer head (11) is coaxially mounted on the end of the cylinder body (12); a mounting portion of the hammer head (11) is axially limited and slidably mounted in the guide hole (124), and an end of the mounting portion extends into the piston chamber (122).

2. The aviation sheet metal rivet hammer according to claim 1, characterized in that: The gear assembly (22) comprises a disc tooth (221) and a semicircular tooth (222); the disc tooth (221) is rotatably mounted in the hammer handle (2) via a bearing, and its mounting axis is perpendicular to the motor output shaft (211); the end of the motor output shaft (211) is a gear structure, meshing with the disc tooth (221) and used to drive the disc tooth (221) to rotate; the semicircular tooth (222) is coaxially fixedly connected to the disc tooth (221); the axial cross section of the semicircular tooth (222) is semicircular in shape as a whole, and a tooth profile is provided on the outer diameter of the semicircle; the semicircular tooth (222) meshes with the spur rack (131) of the piston (13).

3. The aviation sheet metal rivet hammer according to claim 2, characterized in that: The disc teeth (221) and the semicircular teeth (222) are respectively provided with threaded holes next to the central mounting shaft holes, and the two are coaxially superimposed and fixedly connected by screws passing through the threaded holes.

4. The aviation sheet metal rivet hammer according to claim 1, characterized in that: The hammer head (11) comprises a guide rod (111) and a hammering portion (112); the guide rod (111) serves as a mounting portion of the hammer head (11), the guide rod (111) being a cylindrical rod as a whole and coaxially fixed to one side of the hammering portion (112); the side of the hammering portion (112) facing away from the guide rod (111) is a striking surface of the hammer head (11).

5. The aviation sheet metal rivet hammer according to claim 4, characterized in that: The hammer head (11) is axially limited by a limiting assembly (14), and the limiting assembly (14) includes a ball (141), a spring (142), and a screw (143); the hammer head installation end of the cylinder body (12) is provided with a limiting hole (125) vertically penetrating the guide hole (124), and the limiting hole (125) is a threaded hole; the screw (143) is inserted into the limiting hole (125), and the two are threadedly connected; the spring (142) is sleeved on the smooth rod part at the end of the screw (143), one end of the spring (142) is against the threaded part of the screw (143), and the other end is fixed with a ball (141); a slide groove (113) is axially provided on the outer diameter of the guide rod (111), and the ball (141) is elastically pressed into the slide groove (113).

6. The aviation sheet metal rivet hammer according to claim 1, characterized in that: The hammer body (1) further comprises a hammer angle (15), and the hammer angle (15) comprises a connecting portion (151) and a nail removing portion (152); the connecting portion (151) is in the shape of a cover and is threadedly connected to an end of the cylinder body (12) away from the hammer head (11); the nail removing portion (152) is in the shape of a scissors and is fixedly arranged on the outer end surface of the connecting portion (151) and is used for removing nails.

7. The aviation sheet metal rivet hammer according to claim 1, characterized in that: A piston ring (132) is sleeved on the outer wall of one end of the piston (13) close to the air chamber (121). The piston ring (132) is made of rubber and has a sealing function, and is used to increase the compression ratio of nitrogen in the air chamber (121) when the piston (13) moves.

8. The aviation sheet metal rivet hammer according to claim 1, characterized in that: The side wall of the cylinder body (12) is provided with a through hole (126) connected to the air containing chamber (121) and used for filling the air containing chamber (121) with nitrogen.

9. The aviation sheet metal rivet hammer according to claim 1, characterized in that: A control switch (24) is provided in the middle of the hammer handle (2) for controlling the action of the motor (21).

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