CN210762841U

CN210762841U - Detection mechanism

Info

Publication number: CN210762841U
Application number: CN201921226941.1U
Authority: CN
Inventors: 陈浩
Original assignee: Suzhou Sachi Huachen Machinery Co Ltd
Current assignee: Safe Run Intelligent Equipment Co Ltd
Priority date: 2019-07-31
Filing date: 2019-07-31
Publication date: 2020-06-16
Anticipated expiration: 2029-07-31

Abstract

The utility model relates to a test equipment technical field discloses a detection mechanism. The detection mechanism comprises a fixed frame which is used for connecting the feeding frame; the rotating shaft is arranged on the fixed frame; the detection unit is arranged on the rotating shaft and is configured to displace and transmit a material signal when a material passes through the detection unit; and the connecting assembly is configured to be capable of adjusting the angle of the detection unit relative to the fixed frame and fixing the rotating shaft and the fixed frame. Through setting up coupling assembling, coupling assembling is configured to the angle and fixed pivot and the mount that can adjust the relative mount of detecting element, and the detection commonality that can adapt to the material of different thickness has or not is stronger, and can avoid the relative mount of pivot to take place to rotate to drive detecting element and take place to rotate, can improve this detection mechanism's stability, and further improve the accuracy of testing result.

Description

Detection mechanism

Technical Field

The utility model relates to a test equipment technical field especially relates to a detection mechanism.

Background

The detection mechanism that whether carries out the detection to the material is the essential information detection and the information feedback device of realization automated control.

As shown in fig. 1, in the prior art, the detecting mechanism for detecting whether a material exists includes a fixing frame 3 ' connected to the feeding frame, a rotating shaft 1 ' disposed on the fixing frame 3 ' and a detecting unit 2 ' rotatably disposed on the rotating shaft 1 ', and when the material passes through the bottom of the detecting unit 2 ', one end of the detecting unit 2 ' contacting the material is lifted upwards, so as to trigger a material signal. However, in the process of long-term use of the device, the detection mechanism may loosen between the rotating shaft 1 'and the fixing frame 3' due to vibration, which causes false triggering of signals and results in inaccurate detection results.

SUMMERY OF THE UTILITY MODEL

Based on above, an object of the utility model is to provide a detection mechanism can prevent that the pivot is not hard up, makes the testing result more accurate, and can improve this detection mechanism's stability.

In order to achieve the purpose, the utility model adopts the following technical proposal:

a detection mechanism, comprising:

the fixing frame is used for connecting the feeding frame;

the rotating shaft is arranged on the fixed frame;

the detection unit is arranged on the rotating shaft and is configured to be capable of displacing and transmitting a material signal when a material passes through the detection unit;

a connecting assembly configured to be able to adjust an angle of the detecting unit with respect to the fixing frame and fix the rotating shaft and the fixing frame.

As a preferred scheme of detection mechanism, coupling assembling includes middle mounting, first connecting piece and second connecting piece, first connecting piece is used for fixing middle mounting with the pivot, the second connecting piece is used for fixing the mount with middle mounting.

As a preferred scheme of the detection mechanism, a first connection hole is formed in the middle fixing piece, a first through hole is formed in the fixing frame, the rotating shaft penetrates through the first through hole, and the first connection piece penetrates through the first connection hole and is connected with the rotating shaft.

As a preferred scheme of the detection mechanism, an arc-shaped adjusting hole is further formed in the middle fixing piece, a second connecting hole is formed in the fixing frame, and the second connecting piece penetrates through the arc-shaped adjusting hole and the second connecting hole.

As a preferable mode of the detection mechanism, the detection unit includes a first connection arm rotatably connected to the rotating shaft, and one end of the first connection arm can abut against the feeding plane of the feeding frame, and a proximity switch assembly including a proximity switch configured to be triggered and transmit the material signal when the one end of the first connection arm is displaced.

As a preferred scheme of the detection mechanism, the proximity switch assembly further comprises a second connecting arm, the second connecting arm is fixed on the rotating shaft, and one end of the second connecting arm is provided with the proximity switch.

As a preferred scheme of the detection mechanism, a first plane is arranged on the rotating shaft, a second through hole is arranged on the second connecting arm, the rotating shaft penetrates through the second through hole, a first clamping piece is arranged in the second through hole, and the surface of the first clamping piece can abut against the first plane.

As a preferable mode of the detection mechanism, the detection unit further includes a detection wheel rotatably connected to the one end of the first connection arm, and the detection wheel is capable of abutting against a feeding plane of the feeding frame.

As a preferable aspect of the detection mechanism, the detection mechanism further includes a limiting component configured to limit the rotation of the first connection arm.

As a preferred scheme of detection mechanism, spacing subassembly include the third linking arm with set up in stopper on the third linking arm, the third linking arm is fixed in the pivot, the stopper is located the top of first linking arm.

The utility model has the advantages that:

the utility model provides a detection mechanism for whether have the material to pass on the feed holder and detect. By arranging the detection unit, when the material passes through the detection unit, the detection unit can displace and transmit a material signal; after the material passes through the detection unit completely, the material signal can disappear, the detection process is simple, the operation is convenient, and the detection result is more accurate. Through setting up coupling assembling, coupling assembling is configured to the angle and fixed pivot and the mount that can adjust the relative mount of detecting element, and the detection commonality that can adapt to the material of different thickness has or not is stronger, and can avoid the relative mount of pivot to take place to rotate to drive detecting element and take place to rotate, can improve this detection mechanism's stability, and further improve the accuracy of testing result.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required to be used in the description of the embodiments of the present invention will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the contents of the embodiments of the present invention and the drawings without creative efforts.

FIG. 1 is a schematic diagram of a prior art detection mechanism;

fig. 2 is a schematic structural diagram of a detection mechanism provided by the present invention;

fig. 3 is a schematic structural view of an intermediate fixing member in the detection mechanism provided by the present invention;

fig. 4 is a schematic structural view of a fixing frame in the detection mechanism provided by the present invention;

fig. 5 is a schematic structural view of the proximity switch assembly of the detection mechanism according to the present invention;

fig. 6 is a schematic structural diagram of a second connecting arm in the detection mechanism provided by the present invention.

In the figure:

1' -a rotating shaft; 2' -a detection unit; a 3' -proximity switch assembly;

1-a rotating shaft; 11-a first plane;

2-a detection unit; 21-a first connecting arm; 22-detection wheel; 23-a proximity switch assembly; 231-a second connecting arm; 2311-a second via; 2312-a first engaging member; 232-proximity switch;

3-a fixing frame; 31-a first via; 32-second connection hole;

4-a limiting component; 41-a third connecting arm; 42-a limiting block;

5-a connecting assembly; 51-an intermediate fixture; 511-a first connection hole; 512-third connection hole; 513-arc-shaped adjusting holes.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.

In the description of the present invention, unless expressly stated or limited otherwise, the terms "connected," "connected," and "fixed" are to be construed broadly, e.g., as meaning permanently connected, detachably connected, or integral to one another; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meaning of the above terms in the present invention can be understood in specific cases to those skilled in the art.

In the present disclosure, unless expressly stated or limited otherwise, the first feature "on" or "under" the second feature may comprise direct contact between the first and second features, or may comprise contact between the first and second features not directly. Also, the first feature being "on," "above" and "over" the second feature includes the first feature being directly on and obliquely above the second feature, or merely indicating that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature includes the first feature being directly under and obliquely below the second feature, or simply meaning that the first feature is at a lesser elevation than the second feature.

In the description of the present embodiment, the terms "upper", "lower", "right", etc. are used in an orientation or positional relationship based on that shown in the drawings only for convenience of description and simplicity of operation, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first" and "second" are used only for descriptive purposes and are not intended to have a special meaning.

As shown in fig. 2, this embodiment provides a detection mechanism, and this detection mechanism can be used for passing to whether there is the material to detect on the feed frame (not shown in the figure), and pivot 1 among this detection mechanism is connected the fastening with mount 3, and pivot 1 is difficult to produce not hard up, and is more accurate to the testing result that the material has or not.

Specifically, the detection mechanism that this embodiment provided includes pivot 1, detecting element 2 and mount 3, wherein, mount 3 is used for connecting the feed frame, pivot 1 sets up on mount 3, detecting element 2 includes first link arm 21, the one end of first link arm 21 is passed through the bearing spare and is rotated and connect in pivot 1, when there is not the material to pass through, the other end of first link arm 21 can be all the time with the feed plane looks butt of feed frame, when there is the material to pass through on the feed plane of feed frame, the other end of first link arm 21 can be supported in the surface of material, detecting element 2 is configured as when the material that the one end of first link arm 21 and the feed plane butt of feed frame was transferred lifts, the transmission has the material signal.

Through setting up detecting element 2, whether there is the material to transmit on the detection feed frame. When a material passes through one end of the first connecting arm 21, which is far away from the rotating shaft 1, the first connecting arm 21 can rotate relative to the rotating shaft 1, and one end of the first connecting arm, which is far away from the rotating shaft 1, is upwards lifted due to the pushing of the material, so that a material signal is transmitted; when the material completely passes through the first connecting arm 21, the end of the first connecting arm 21 far away from the rotating shaft 1 falls down, so that the material signal disappears.

Further, because the feeding frame of the forming machine has a micro-vibration phenomenon in the using process, the rotating shaft 1 can be loosened due to vibration after being used for a long time, so that the rotating shaft 1 rotates relative to the fixed frame 3, and the material signal is triggered by mistake. In the present embodiment, the detecting mechanism further includes a connecting assembly 5, and the connecting assembly 5 is configured to be able to adjust an angle of the detecting unit 2 relative to the fixing frame 3 and fix the rotating shaft 1 and the fixing frame 3. Specifically, the connecting assembly 5 includes a middle fixing member 51, a first connecting member for fixing the middle fixing member 51 and the rotating shaft 1, and a second connecting member for fixing the fixing frame 3 and the middle fixing member 51. Through setting up middle mounting 51, and middle mounting 51 is respectively through first connecting piece and second connecting piece and pivot 1 and mount 3 fixed connection, make pivot 1 and mount 3 relatively fixed, can avoid pivot 1 relatively fixed frame 3 to take place to rotate, and drive first connecting arm 21 and take place to rotate, cause the unsafe phenomenon of testing result, this detection mechanism testing process is simple, high durability and convenient use, the testing result is more accurate, and can improve this detection mechanism's stability.

Further, as shown in fig. 3-4, a first connection hole 511 is formed in the middle fixing member 51, a first through hole 31 is formed in the fixing frame 3, the rotating shaft 1 is inserted into the first through hole 31, the rotating shaft 1 is fixedly connected to the middle fixing member 51 through at least one first connection member, and the first connection member is inserted into the first connection hole 511; in addition, the middle fixing member 51 is further provided with an arc-shaped adjusting hole 513, the fixing frame 3 is provided with a second connecting hole 32, and the second connecting member is arranged in the arc-shaped adjusting hole 513 and the second connecting hole 32 in a penetrating manner.

Preferably, in the present embodiment, the first connection hole 511 and the second connection hole 32 are both threaded holes, and the first connection member and the second connection member are both screws or bolts. In the present embodiment, the first connecting member and the second connecting member are exemplified by screws. The screw connection has the advantages of simple processing and convenient disassembly and assembly. After multiple uses, if the middle fixing member 51 is damaged, the first connecting member and the second connecting member can be removed, and then the middle fixing member 51 can be replaced with a new one, so that the maintenance cost is reduced.

Through setting up arc regulation hole 513, pass first connecting hole 511 and be fixed in the pivot 1 back on middle mounting 51 when first connecting piece, can rotate middle mounting 51 and pivot 1 according to the different thickness of material to the angle between adjustment pivot 1 and the mount 3, with the material of adaptation different thickness.

Preferably, the middle fixing member 51 is further provided with a third connecting hole 512, in this embodiment, the third connecting hole 512 may be a pin hole, and a pin is inserted into the third connecting hole 512 and connected to the fixing frame 3, so as to further fix the fixing frame 3 and the middle fixing member 51.

In this embodiment, the middle fixing member 51 has a disk shape, and the number of the arc adjusting holes 513 provided thereon is two, two arc adjusting holes 513 are oppositely provided, the number of the third connecting holes 512 is two, and two third connecting holes 512 are oppositely provided. The first connecting member, the second connecting member and the pins are distributed along the circumferential direction of the intermediate fixing member 51, so that the intermediate fixing member 51 is firmly fixed to the fixing frame 3. Of course, the number of first connecting piece, second connecting piece and pin does not do the restriction, and a plurality of first connecting pieces, a plurality of second connecting pieces and a plurality of pin all can be along the even and interval setting of middle mounting 51's circumference to it is even to guarantee that the atress is even on the middle mounting 51, improves fixed effect.

Of course, in other embodiments, if the middle fixing member 51 does not need to be replaced frequently, the rotating shaft 1 may also be welded to the middle fixing member 51 through the first through hole 31, and the middle fixing member 51 is welded to the fixing frame 3, or other manners capable of fixedly connecting the middle fixing member 51 to the rotating shaft 1 and the fixing frame 3, respectively, are adopted.

Preferably, the detecting unit 2 further comprises a detecting wheel 22, the detecting wheel 22 is rotatably connected to one end of the first connecting arm 21 away from the rotating shaft 1, and when no material passes through the feeding plane of the feeding frame, the detecting wheel 22 can abut against the feeding plane of the feeding frame; the detection wheel 22 is able to abut against the surface of the material when it passes through the feeding plane of the feeding frame. Through setting up detection wheel 22, when the material through detecting wheel 22, detection wheel 22 can rotate along with the motion of material to reduce the friction between first connecting arm 21 and the material, avoid the surperficial wearing and tearing that take place of material, and can reduce on the first connecting arm 21 and take place wearing and tearing with the one end of material contact, prolong the life of first connecting arm 21.

Further, as shown in fig. 2, the detection mechanism 2 further includes a proximity switch assembly 23, wherein the proximity switch assembly 23 includes a second connecting arm 231 and a proximity switch 232, the second connecting arm 231 is fixed on the fixing frame 3, the proximity switch 232 is disposed on the second connecting arm 231 at a side close to the detection wheel 22, and the proximity switch 232 is configured to be triggered and transmit a material signal when one end of the first connecting arm 21 is lifted. Preferably, a trigger is provided on the first connecting arm 21, and the trigger is configured to trigger the proximity switch 232. Through setting up proximity switch subassembly 23, when the trigger piece on first connecting arm 21 was close to proximity switch 232's response region, proximity switch 232 can sense the trigger piece rapidly thereby to trigger there is material signal, and the testing process is more convenient. In this embodiment, the trigger is made of a metal material, in particular ferrous metal. The proximity switch 232 is a sensor, and when the proximity switch 232 is a displacement sensor, it can not only sense whether the trigger exists, but also accurately reflect the position and the stroke of the trigger.

Preferably, the detection mechanism further comprises a controller (not shown), the proximity switch 232 is electrically connected to the controller, and when the trigger moves into the sensing area of the proximity switch 232, the proximity switch 232 is triggered and transmits a material signal to the controller. The specific connection manner in which the proximity switch 232 is electrically connected to the controller is conventional in the art and will not be described in detail herein, and the specific type and configuration of the proximity switch 232 and the controller are conventional and will not be described in detail herein.

Specifically, when the material passes through the detection wheel 22, the detection wheel 22 is lifted upwards, so that the trigger part is close to the sensing area of the proximity switch 232, and the proximity switch 232 is triggered, so that the proximity switch 232 transmits a material signal to the controller.

In the prior art, the second connecting arm 231 is fixed at one end of the rotating shaft 1, and two semicircular rings are usually used to lock the rotating shaft 1, but the detection mechanism is vibrated in the long-term use process, the second connecting arm 231 can rotate relative to the rotating shaft 1, and when the second connecting arm 231 rotates downwards to enable the trigger to enter the sensing area of the proximity switch 232, the proximity switch 232 can continuously transmit a material signal, so that misjudgment is caused. In order to solve the problem, as shown in fig. 5 to fig. 6, a first plane 11 is disposed on the rotating shaft 1, a second through hole 2311 is disposed on the second connecting arm 231, the rotating shaft 1 is inserted into the second through hole 2311, a first engaging member 2312 is disposed in the second through hole 2311, and a surface of the first engaging member 2312 can abut against the first plane 11. By providing the first plane 11 on the rotating shaft 1 and providing the first engaging piece 2312 on the second connecting arm 231, which can abut against the first plane 11, the second connecting arm 231 can be prevented from rotating relative to the rotating shaft 1 and affecting the detection result.

Of course, in other embodiments, the second connecting arm 231 may also be welded to the rotating shaft 1, and since the rotating shaft 1 is fixed relative to the fixing frame 3, the second connecting arm 231 will not rotate.

Further, as shown in fig. 5, the detection mechanism further includes a limiting assembly 4, and the limiting assembly 4 is configured to limit the rotation of the detection unit 2. When the material passes through detection wheel 22 fast, detection wheel 22 lifts up suddenly, gets into proximity switch 232's induction area, but because inertia, detection wheel 22 still can continue to rise a section distance (jump the wheel phenomenon promptly), if detection wheel 22 upward movement is outside proximity switch 232's induction area, then there is the material signal to disappear, then detection wheel 22 receives the action of gravity to fall back to the material surface then regeneration again has the material signal, like this, the signal just forms one from having to not having to having again to some phenomenon, can cause the erroneous judgement of controller. This embodiment can carry on spacingly to detecting element 2's rotation through setting up spacing subassembly 4, avoids appearing aforementioned erroneous judgement phenomenon to it is more accurate to make the testing result.

Specifically, the limiting component 4 includes a third connecting arm 41 and a limiting block 42, the third connecting arm 41 is fixed on the rotating shaft 1, and the limiting block 42 is disposed on the third connecting arm 41. Preferably, the vertical distance between the proximity switch 232 and the limit block 42 is the same as the thickness of the material, so that the detection wheel 22 cannot exceed the sensing area of the proximity switch 232 even if moving upwards due to inertia.

In order to prevent the limiting component 4 from rotating relative to the rotating shaft 1, the detecting unit 2 is abutted against one end of the material and cannot be lifted, so that the transmission of the material is affected, in the embodiment, the rotating shaft 1 is provided with a second plane, the third connecting arm 41 is provided with a third through hole, the rotating shaft 1 penetrates through the third through hole, the third through hole is internally provided with a second clamping piece, and the surface of the second clamping piece can be abutted against the second plane. Through set up the second plane in pivot 1, set up the second fastener that can lean on with the second plane on spacing subassembly 4, can prevent that spacing subassembly 4 from taking place to rotate for pivot 1, influencing spacing effect.

In this embodiment, the first connecting arm 21 is disposed between the proximity switch assembly 23 and the position-limiting assembly 4. Of course, in other embodiments, other arrangements of the first connecting arm 21, the limit assembly 4 and the proximity switch assembly 23 may be adopted as long as the above-mentioned functions can be achieved.

For the sake of easy understanding, the adjustment process of the detection mechanism is briefly described in conjunction with fig. 1 to 6:

(1) the rotating shaft 1 is arranged in the first through hole 31 in a penetrating manner, and the first connecting piece is arranged in the first connecting hole 511 in a penetrating manner and is fixedly connected with the rotating shaft 1;

(2) according to the thickness of the material, the middle fixing piece 51 is rotated, the rotating shaft 1 is driven to rotate until the detecting unit 2 has a proper angle relative to the feeding frame, and then the second connecting piece is sequentially arranged in the arc-shaped adjusting hole 513 and the second connecting hole 32 in a penetrating manner, so that the middle fixing piece 51 is fixedly connected with the fixing frame 3;

(3) the pin is inserted into the third connecting hole 512 and connected to the fixing frame 3.

In addition, the working process of the detection mechanism is as follows:

(1) when the material passes through the bottom of the detection wheel 22, the detection wheel 22 rotates along with the movement of the material and is lifted upwards to drive the trigger to move into the sensing area of the proximity switch 232, the proximity switch 232 transmits a material signal to the controller, and when the first connecting arm 21 is abutted to the limiting block 42, the detection wheel 22 moves downwards to be abutted to the material;

(2) when the material completely passes through the detection wheel 22, the detection wheel 22 falls down to drive the trigger member to move out of the sensing area of the proximity switch 232, and the material signal disappears.

In addition, the detection mechanism can measure the size of the material passing through the feeding frame. When the detection mechanism is used for measuring the length of the material, the controller records the duration of the material signal, and then the length of the material can be obtained by multiplying the transfer speed of the material by the duration of the material signal.

The utility model provides a detection mechanism's testing process is simple, convenient operation, and the testing result is more accurate.

It should be noted that the foregoing is only a preferred embodiment of the present invention and the technical principles applied. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail with reference to the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the scope of the present invention.

Claims

1. A detection mechanism, comprising:

the fixing frame (3) is used for connecting the feeding frame;

the rotating shaft (1) is arranged on the fixed frame (3);

the detection unit (2) is arranged on the rotating shaft (1), and the detection unit (2) is configured to be capable of displacing and transmitting a material signal when a material passes through the detection unit (2);

a connecting assembly (5), wherein the connecting assembly (5) is configured to be capable of adjusting the angle of the detection unit (2) relative to the fixing frame (3) and fixing the rotating shaft (1) and the fixing frame (3).

2. The detection mechanism according to claim 1, wherein the connecting assembly (5) comprises an intermediate fixing member (51), a first connecting member for fixing the intermediate fixing member (51) and the rotation shaft (1), and a second connecting member for fixing the fixing frame (3) and the intermediate fixing member (51).

3. The detecting mechanism according to claim 2, wherein a first connecting hole (511) is formed in the middle fixing member (51), a first through hole (31) is formed in the fixing frame (3), the rotating shaft (1) is inserted into the first through hole (31), and the first connecting member is inserted into the first connecting hole (511) and connected to the rotating shaft (1).

4. The detection mechanism according to claim 2, wherein an arc-shaped adjusting hole (513) is further formed in the middle fixing member (51), a second connecting hole (32) is formed in the fixing frame (3), and the second connecting member is inserted into the arc-shaped adjusting hole (513) and the second connecting hole (32).

5. The detection mechanism according to claim 1, wherein the detection unit (2) comprises a first connecting arm (21) and a proximity switch assembly (23), the first connecting arm (21) is rotatably connected to the rotating shaft (1), one end of the first connecting arm (21) can abut against a feeding plane of the feeding frame, the proximity switch assembly (23) comprises a proximity switch (232), and the proximity switch (232) is configured to be triggered and transmit the material signal when the one end of the first connecting arm (21) is displaced.

6. The detection mechanism according to claim 5, wherein the proximity switch assembly (23) further comprises a second connecting arm (231), the second connecting arm (231) is fixed on the rotating shaft (1), and one end of the second connecting arm (231) is provided with the proximity switch (232).

7. The detection mechanism according to claim 6, wherein a first plane (11) is disposed on the rotating shaft (1), a second through hole (2311) is disposed on the second connecting arm (231), the rotating shaft (1) is inserted into the second through hole (2311), a first engaging member (2312) is disposed in the second through hole (2311), and a surface of the first engaging member (2312) can abut against the first plane (11).

8. The detection mechanism according to claim 5, characterized in that the detection unit (2) further comprises a detection wheel (22), the detection wheel (22) being rotatably connected to the one end of the first connecting arm (21), the detection wheel (22) being capable of abutting against a feeding plane of the feeding frame.

9. The detection mechanism according to claim 5, further comprising a stop assembly (4), the stop assembly (4) being configured to stop rotation of the first connecting arm (21).

10. The detection mechanism according to claim 9, wherein the limiting component (4) comprises a third connecting arm (41) and a limiting block (42) arranged on the third connecting arm (41), the third connecting arm (41) is fixed on the rotating shaft (1), and the limiting block (42) is located above the first connecting arm (21).