Adjustable dumbbell structure and weight plate thereof and weight plate unlocking method

Abstract

An adjustable dumbbell (100, fig.1) comprising a plurality of detachably connectable and stackable weight plates 21, each with convex and concave combining portions (211, 50, 212, 60, fig.2), and a ha

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to dumbbells for fitness activities such as weight training and more particularly, to an adjustable dumbbell structure and a weight plate thereof and a weight plate unlocking method, which allow the user to quickly and conveniently adjust the required number of weight plates to make the weight of the dumbbell meet the fitness requirement of the user. 2. Description of the Related Art Dumbbells are exercise equipment commonly used by the general public today. Traditional dumbbells are monolithically formed, and cannot be adjusted in weight. Training with varying levels of resistance requires a dumbbell set containing multiple dumbbells of different weights, such as the ‘weight training intelligence system’ disclosed in Taiwan Patent No. M581492. Some dumbbells allow the users to adjust the overall weight by movably adding or removing weight plates at both ends of the handle, such as the ‘dumbbell set for easy storage’ disclosed in Taiwan Patent No. 1576135. With respect to the above-described type of dumbbell that allows the user to add or remove weight plates to adjust the weight, the user's primary concern is the convenience of adding and removing the weight plate. However, the conventional dumbbells of this type are mostly still too cumbersome when it comes to weight adjustment. Some require the entire set of weight plates to be removed before selecting and installing the desired number of weight plates, or have overly complex mechanisms for adding and removing the weight plate, which may sometimes lead to user errors during adjustment. The user may only realize that the dumbbell is too heavy or too light when holding and using it. In addition, some dumbbells use an interlocking mechanism between the weight plates, requiring the user to operate a switching mechanism on each weight plate to release or lock the connection between the weight plates during weight adjustment. Therefore, the user has to individually operate the switching mechanism on each weight plate. If any confusion occurs during the adjustment process, the user has to check the switching mechanisms on the weight plates one by one, which is overly cumbersome for the user. Besides, the switching mechanisms are overly complex and involve numerous components, leading to increased maintenance and repair costs. SUMMARY OF THE INVENTION The present invention has been accomplished in view of the above-noted circumstances. It is a primary objective of the present invention to provide an adjustable dumbbell structure and a weight plate thereof and a weight plate unlocking method, which allow the user to quickly and conveniently adjust the number of the weight plates of the dumbbell to make the weight of the dumbbell meet the need of the user, and quickly readjust if the weight is not suitable, so as to save adjustment time, and prevent the dumbbell from overly complex mechanisms and the resulting drawback of high maintenance and repair costs. To attain the above objective, the present invention provides an adjustable dumbbell structure which includes at least one adjustable weight unit, a handle assembly, and at least one control member. The adjustable weight unit includes a plurality of weight plates. The weight plates are detachably combined in a stacked manner. Each of the weight plates includes a first combining portion and a second combining portion, which are located on two sides of the weight plate respectively. For every two adjacent weight plates, the first combining portion of one of the weight plates is detachably combined with the second combining portion of the other of the weight plates. The handle assembly includes a handle, and at least one combining member fixed to the handle. The combining member includes a third combining portion. The third combining portion is detachably combined with one of the first combining portion and the second combining portion of one of the weight plates of the adjustable weight unit. The adjustable dumbbell structure includes a plurality of concave combining portions, and a plurality of convex combining portions. Each of the concave combining portions includes at least one lock groove. Each of the convex combining portions includes an inner space, at least one locking piece disposed in the inner space, and at least one operation opening and at least one lock opening, which communicate with the inner space. The locking piece includes a locking part. The locking piece is switchable between a locking position and a non-locking position by being controlled by the control member which is inserted in the inner space through the operation opening. The first combining portion of each of the weight plates is the aforementioned convex combining portion. The second combining portion of each of the weight plates is the aforementioned concave combining portion. The third combining portion of the handle assembly is one of the aforementioned convex combining portion and concave combining portion. When one of the convex combining portions is combined with one of the concave combining portions, the locking piece of the convex combining portion is located at the locking position, and the locking part of the locking piece protrudes out of the lock opening, and is engaged with the lock groove of the concave combining portion. When the locking piece is switched to the non-locking position, the locking part is moved toward the inner space and disengaged from the lock groove. To attain the above objective, the present invention provides a weight plate of an adjustable dumbbell structure, which is adapted to be unlocked by a control member. The weight plate includes a concave combining portion and a convex combining portion, which are located on two sides of the weight plate respectively. The concave combining portion includes a lock groove. The convex combining portion includes an inner space, a locking piece disposed in the inner space, and an operation opening and a lock opening, which communicate with the inner space. The locking piece includes a locking part. The locking piece is switchable between a locking position and a non-locking position by being controlled by the control member which is inserted in the inner space through the operation opening. When the locking piece of the convex combining portion is located at the locking position, the locking part of the locking piece protrudes out of the lock opening for being engaged with the lock groove of the concave combining portion of another weight plate. When the locking piece of the convex combining portion is switched from the locking position to the non-locking position, the locking part of the locking piece is moved toward the inner space for being disengaged from the lock groove. To attain the above objective, the present invention provides a weight plate unlocking method for an adjustable dumbbell structure. The weight plate unlocking method includes the steps of: providing an adjustable dumbbell structure, the adjustable dumbbell structure including a plurality of weight plates, the weight plates being detachably combined in a stacked manner, each of the weight plates including a concave combining portion and a convex combining portion, the concave combining portion and the convex combining portion being located on two sides of the weight plate respectively, the concave combining portion including a lock groove, the convex combining portion including an inner space, a locking piece disposed in the inner space, and an operation opening and a lock opening, which communicate with the inner space, for every two adjacent weight plates, the convex combining portion of one of the weight plates being detachably combined with the concave combining portion of the other of the weight plates in a way that a locking part of the locking piece of the convex combining portion protrudes out of the lock opening, and is engaged with the lock groove of the concave combining portion; providing a control member, and making the control member inserted in the inner space through the operation opening of one of the weight plates and directly or indirectly connected with the locking piece; and using the control member to move the locking piece, making the locking part of the locking piece moved toward the inner space to be disengaged from the lock groove. As a result, before using the adjustable dumbbell structure, the user can operate the control member at the operation opening of the convex combining portion of one of the weight plates corresponding to the desired number of weight plates. By operating the control member by a simple and quick action to switch the locking piece of the convex combining portion of the controlled weight plate to the non-locking position, the engagement between the convex combining portion of the controlled weight plate and the concave combining portion of the adjacent weight plate can be released. At this time, the two weight plates can be separated from each other, such that the handle assembly is installed with only the number of weight plates the user desires. When the weight plates are to be combined again, the user only needs to operate the control member by the same simple and quick action again to switch the locking piece of the convex combining portion of the to-be combined weight plate to the non-locking position, such that the convex combining portion can be coupled with the concave combining portion of the other to-be combined weight plate. After that, switching the locking piece of the convex combining portion to the locking position can combine the weight plates with each other firmly. Therefore, the present invention allows the user to quickly and conveniently adjust the number of the weight plates of the dumbbell to make the weight of the dumbbell meet the need of the user. Even if the weight is not suitable, it can be quickly adjusted again, thereby saving the adjustment time. Besides, the structure of the present invention is not overly complex, which can avoid high repair and maintenance costs. Another advantage of the present invention is that it is not limited to the existing number of weight plates. The users can increase or decrease the number of weight plates according to their own needs so that users of different strengths can use it. Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the scope of the invention will become apparent to those skilled in the art from this detailed description. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an assembled perspective view of an adjustable dumbbell structure according to a first preferred embodiment of the present invention. FIG. 2 is an exploded perspective view of the adjustable dumbbell structure. FIG. 3 is an exploded perspective view showing a base and a control member of the adjustable dumbbell structure. FIG. 4 and FIG. 5 are exploded perspective views of a positioning member of the base and the control member. FIG. 6 is a sectional view of a part of the base and the control member taken along the line 6-6 in FIG. 2. FIG. 7 is an assembled perspective view of a handle assembly of the adjustable dumbbell structure. FIG. 8 is an assembled perspective view of a weight plate of the adjustable dumbbell structure. FIG. 9 is an exploded perspective view of the weight plate. FIG. 10 is another assembled perspective view of the weight plate. FIG. 11 is a sectional view of a part of the handle assembly and weight plates of the adjustable dumbbell structure taken along the line 11-11 in FIG. 2. FIG. 12 is a sectional view of a part of the adjustable dumbbell structure taken along the line 12-12 in FIG. 1. FIG. 13 is a top view of a part of the adjustable dumbbell structure. FIG. 14 is a perspective view of a part of the adjustable dumbbell structure, showing that the control member will be inserted into one of the weight plates. FIG. 15 is a sectional view taken along the line 15-15 in FIG. 14. FIG. 16 is similar to FIG. 15, but showing the status that the control member has been inserted into the weight plate, and a guiding bevel of a driving portion of the control member pushes a pillar. FIG. 17 is similar to FIG. 16, but showing the status that the control member is further inserted into the weight plate, and the pillar is elastically pushed by an elastic member to be engaged with an arc recess of the control member. FIG. 18 is an assembled perspective view of an adjustable dumbbell structure according to a second preferred embodiment of the present invention. FIG. 19 is an exploded perspective view of the adjustable dumbbell structure. FIG. 20 is an assembled perspective view of a weight plate of the adjustable dumbbell structure. FIG. 21 is an exploded perspective view of the weight plate. FIG. 22 is approximately a top view of the weight plate, but not showing a second plate and a third plate. FIG. 23 and FIG. 24 are sectional views of the adjustable dumbbell structure, showing the process of a control member of the adjustable dumbbell structure being inserted into the weight plate. FIG. 25 and FIG. 26 are assembled perspective views of a weight plate and a control member of an adjustable dumbbell structure according to a third preferred embodiment of the present invention. FIG. 27 is an exploded perspective view of the weight plate and the control member. FIG. 28 is a front view of FIG. 26, showing that the control member is located at a retraction position. FIG. 29 is similar to FIG. 28, but showing that the control member is located at a reach-out position. FIG. 30 to FIG. 32 are assembled perspective views of a weight plate and a control member of an adjustable dumbbell structure according to a fourth preferred embodiment of the present invention. FIG. 33 is an exploded perspective view of the weight plate and the control member. FIG. 34 is approximately a front view of FIG. 32, but not showing a third plate, and showing that the control member is located at a first angular position. FIG. 35 is similar to FIG. 34, but showing that the control member is located at a second angular position. FIG. 36 and FIG. 37 are assembled perspective views of a weight plate of an adjustable dumbbell structure according to a fifth preferred embodiment of the present invention. FIG. 38 is an exploded perspective view of the weight plate and a control member. FIG. 39 is approximately a front view of FIG. 37, but additionally showing the control member, not showing a third plate, and showing that a locking piece is located at a non-locking position. FIG. 40 is similar to FIG. 39, but showing that the locking piece is located at a locking position. DETAILED DESCRIPTION OF THE INVENTION First of all, it is to be mentioned that same or similar reference numerals used in the following embodiments and the appendix drawings designate same or similar elements or the structural features thereof throughout the specification for the purpose of concise illustration of the present invention. It should be noticed that for the convenience of illustration, the components and the structure shown in the figures are not drawn according to the real scale and amount, and the features mentioned in each embodiment can be applied in the other embodiments if the application is possible in practice. Besides, when it is mentioned that an element is disposed on another element, it means that the former element is directly disposed on the latter element, or the former element is indirectly disposed on the latter element through one or more other elements between aforesaid former and latter elements. When it is mentioned that an element is directly disposed on another element, it means that no other element is disposed between aforesaid former and latter elements. Referring to FIG. 1 and FIG. 2, an adjustable dumbbell structure 100 according to a first preferred embodiment of the present invention includes a base 10, two adjustable weight units 20, a handle assembly 30, and two control members 40. Only one of the control members 40 disposed on one side of the base 10 is shown in the figures of this embodiment. The other control member 40 is disposed on the other side of the base 10. It can be seen in FIG. 2 that the two adjustable weight units 20 and the handle assembly 30 collectively compose a dumbbell. As shown in FIG. 2 to FIG. 6, the base 10 includes a frame 11, and two positioning members 12 disposed on two sides of the inner wall of the frame 11. As shown in FIG. 7, the handle assembly 30 includes a handle 31, and two combining members 32 fixedly combined to two ends of the handle 31 respectively. As shown in FIG. 2 and FIGS. 8-10, each of the adjustable weight units 20 includes a plurality of weight plates 21 detachably combined in a stacked manner. In this embodiment, each adjustable weight unit 20 includes three weight plates, but the amount of the weight plates is unlimited thereto. Each of the weight plates 21 includes a first combining portion 211 and a second combining portion 212, which are located on two sides of the weight plate respectively. For every two adjacent weight plates 21, the first combining portion 211 of one of the weight plates is detachably combined with the second combining portion 212 of the other of the weight plates, so that the plurality of weight plates 21 are stacked and combined into the adjustable weight unit 20. Besides, each of the combining members 32 of the aforementioned handle assembly 30 includes a third combining portion 321. The two adjustable weight units 20 are detachably combined with the third combining portions 321 of the two combining members 32 respectively. Furthermore, each of the positioning members 12 of the aforementioned base 10 includes a fourth combining portion 123. In the status shown in FIG. 1, the two adjustable weight units 20 are detachably combined with the fourth combining portions 123 of the two positioning members 12 respectively. Further speaking, the first combining portion 211 of each of the weight plates 21 is a convex combining portion 50, and the second combining portion 212 of each of the weight plates 21 is a concave combining portion 60. Since each of the third combining portions 321 of the handle assembly 30 in this embodiment is combined with the first combining portion 211 of one of the weight plates 21, each of the third combining portions 321 is the same with the second combining portion 212 of the weight plate 21. That is, each of the third combining portions 321 is a concave combining portion 60. Besides, each of the fourth combining portions 123 of the base 10 in this embodiment is combined with the second combining portion 212 of one of the weight plates 21, so each of the fourth combining portions 123 is the same with the first combining portion 211 of the weight plate 21. That is, each of the fourth combining portions 123 is a convex combining portion 50. However, the present invention can be modified in a way that the third combining portion 321 of the handle assembly 30 is combined with the second combining portion 212 of the weight plate 21, and the fourth combining portion 123 of the base 10 is combined with the first combining portion 211 of the weight plate 21. In such case, the third combining portion 321 is a convex combining portion 50, and the fourth combining portion 123 is a concave combining portion 60. It can be known from the above description that the adjustable dumbbell structure 100 includes a plurality of convex combining portions 50 and a plurality of concave combining portions 60. The combination between the weight plates 21, the combination between the weight plate 21 and the combining member 32 of the handle assembly 30, and the combination between the weight plate 21 and the positioning member 12 of the base 10, are all realized by the combination of the convex combining portion 50 with the concave combining portion 60, that will be further described hereinafter. As shown in FIG. 2 and FIG. 3, the frame 11 of the base 10 includes two frame plates 111. Each of the frame plates 111 includes an extending section Illa, and two connecting sections 111b perpendicularly extending from two ends of the extending section Illa respectively. As shown in FIG. 4 and FIG. 5, each of the positioning members 12 includes an outer piece 121 and a blocking piece 122. The outer piece 121 is fastened to one side of the blocking piece 122 by bolts. The fourth combining portion 123 is fastened to another side of the blocking piece 122 by bolts. The outer piece 121 includes an inner side 121a, and an outer side 121b opposite to the inner side 121a. The inner side 121a is fixed to the blocking piece 122. The outer side 121b is recessed with a connecting groove 121c. The two frame plates 111 are disposed on two opposite outer edges of each of the positioning members 12 respectively, and symmetric to each other. The two connecting sections 111b of each of the frame plates 111 are fastened in the connecting grooves 121c of the outer pieces 121 of the two positioning members 12 respectively by bolts. As a result, the frame 11 composed of the two frame plates 111 includes two inside surfaces 112 facing each other, and the two positioning members 12 are fixed to the two inside surfaces 112 respectively. The fourth combining portions 123 of the two positioning members 12 face each other for being detachably combined with the two adjustable weight units 20 respectively. In this way, the two positioning members 12 and the frame 11 can be firmly combined to form the base 10 for the dumbbell composed of the two adjustable weight units 20 and the handle assembly 30 to be securely placed on the base 10 when not in use. Besides, the two adjustable weight units 20 are adapted for the user to remove a part of the weight plates 21 to adjust the weight of the dumbbell. The removed weight plates 21 can be securely stored on the base 10. As shown in FIG. 5, a temporary storage space 124 and an access opening 125 communicating with the temporary storage space 124 are formed between the outer piece 121 and the blocking piece 122 of each of the positioning members 12 of the base 10 for the control member 40 to be inserted into the temporary storage space 124 through the access opening 125 for temporary storage. In other words, the temporary storage space 124 is configured for the user, when not in need of using the control member 40, to insert the control member 40 in the temporary storage space 124 to prevent the control member 40 form getting lost. Furthermore, the outer piece 121 is formed with a buckle recess 121 d located correspondingly to the temporary storage space 124 and the access opening 125, and an engaging rib 121 f protruding from each of two side walls 121e of the buckle recess 121 d. When the control member 40 is inserted in the temporary storage space 124 through the access opening 125, a control portion 41 located at the topmost end of the control member 40 is exposed in the buckle recess 121d. Besides, the control portion 41 of the control member 40 has a plurality of arc engaging recesses 411 the same in amount with and corresponding in position to the engaging ribs 121f. When the control member 40 is inserted in the temporary storage space 124, the arc engaging recesses 411 are engaged with the engaging ribs 121f and positioned, such that the control member 40 is temporarily stored in the temporary storage space 124 more securely, thereby prevented from falling off and getting lost. Referring to FIG. 4 to FIG. 10, each of the convex combining portions 50 of the adjustable dumbbell structure 100, i.e. each of the fourth combining portions 123 and the first combining portions 211 in this embodiment, includes a first plate 51, a second plate 52, and a third plate 53. The first plate 51, the second plate 52 and the third plate 53 are stacked to form an inner space 54. Specifically speaking, the first plate 51 has a lock opening 512 formed on an outer edge 511 of the first plate 51, and a locking piece accommodating groove 513 extending into the first plate 51 from the lock opening 512 in a first direction (i.e. the positive direction of Y-axis shown in FIG. 4 and FIG. 9), which means the locking piece accommodating groove 513 communicates with the lock opening 512. The second plate 52 has an operation opening 522 formed on an outer edge 521 of the second plate 52, and a control member accommodating groove 523 extending into the second plate 52 from the operation opening 522 in a second direction (i.e. the negative direction of Z-axis shown in FIG. 4 and FIG. 9), which means the control member accommodating groove 523 communicates with the operation opening 522. The control member accommodating groove 523 extends in the same direction with the temporary storage space 124 of the base 10. The operation opening 522 and the access opening 125 are toward the same direction. The control member accommodating groove 523 and the locking piece accommodating groove 513 collectively compose the inner space 54. That is, the operation opening 522 and the lock opening 512 communicate with the inner space 54. The third plate 53 has a slide groove 531 extending transversely along Y-axis, which means the slide groove 531 is parallel to the locking piece accommodating groove 513. In this embodiment, each of the convex combining portions 50 is formed at the upper end thereof with the operation opening 522, and formed on a lateral side thereof with the lock opening 512. However, the positions of the operation opening 522 and the lock opening 512 in the present invention are unlimited thereto. Each of the convex combining portions 50 further includes an elastic lock assembly 70 installed in the inner space 54. In other words, the adjustable dumbbell structure 100 includes a plurality of elastic lock assemblies 70. The amount of the elastic lock assemblies 70 is equal to the amount of the convex combining portions 50. Each of the elastic lock assemblies 70 includes an elastic member 71, a locking piece 72, and a pillar 73. The elastic member 71 includes a first end 711 and a second end 712. The first end 711 is attached to the inner surface of the inner space 54. The second end 712 is attached to an end of the locking piece 72. In this embodiment, the locking piece accommodating groove 513 is provided therein with a recess-shaped positionally limiting part 514. The first end 711 of the elastic member 71 is accommodated in the positionally limiting part 514, and elastically pressed on the bottom surface of the positionally limiting part 514. The second end 712 is attached to the locking piece 72. The locking piece 72 is slidably disposed in the locking piece accommodating groove 513. The pillar 73 is attached to one side of the locking piece 72, and protrudes into the control member accommodating groove 523. The terminal end of the pillar 73 is slidably disposed in the slide groove 531 of the third plate 53. In this way, the part of the pillar 73 located in the control member accommodating groove 523 is located correspondingly to the operation opening 522, as shown in FIG. 13. That is, the pillar 73 is partially located below the operation opening 522. Therefore, when the user inserts the control member 40 into the control member accommodating groove 523 through the operation opening 522 as shown in FIG. 14, the control member 40 will be pressed on the pillar 73, so as to make the elastic lock assembly 70 operate, that will be specified hereinafter. Referring to FIG. 7 to FIG. 9, each of the concave combining portions 60 of the adjustable dumbbell structure 100, i.e. each of the third combining portions 321 and the second combining portions 212 in this embodiment, includes a main plate 61, two front plates 62, and two rear plates 63. The two rear plates 63 are spaced for a distance, and fixed on one side of the main plate 61. Then, the two front plates 62 are piled on the two rear plates 63 respectively. An assembling groove 64 is formed between the main plate 61, the two front plates 62 and the two rear plates 63. At least one of the front plates 62 is provided on one side thereof, which faces toward the assembling groove 64, with a lock groove 621. The convex combining portions 50 are detachably combined to the assembling grooves 64 of the concave combining portions 60. That is, as shown in FIG. 11, the plurality of weight plates 21 of each of the adjustable weight units 20 are combined in a stacked manner through the combination of the convex combining portion 50 with the concave combining portion 60, and the convex combining portion 50 of one of the weight plates 21 is combined with the concave combining portion 60 of the handle assembly 30. Furthermore, as shown in FIG. 12, the concave combining portion 60 of another weight plate 21 of each of the adjustable weight units 20 is combined with the convex combining portion 50 of the base 10. The convex combining portions 50 are combined with the concave combining portions 60 in a way that the locking piece 72 of each of the convex combining portions 50 is engaged with the lock groove 621 of the associated concave combining portion 60, that will be specified hereinafter. As shown in FIG. 15, when one of the convex combining portions 50 and one of the concave combining portions 60 are combined with each other, the locking piece 72 of the convex combining portion 50 is elastically pushed by the elastic member 71, thereby normally located at a locking position Pl. When the locking piece 72 is located at the locking position Pl, a locking part 721 of the locking piece 72 protrudes out of the lock opening 512. The locking piece 72 of the convex combining portion 50 is located correspondingly to the lock groove 621 of the concave combining portion 60. Therefore, when the locking piece 72 is located at the locking position Pl, the locking part 721 thereof can be engaged with the lock groove 621 of the concave combining portion 60. At this time, the convex combining portion 50 and the concave combining portion 60 are engaged with each other firmly and reliably. After the user inserts the control member 40 into the operation opening 522 of anyone of the convex combining portions 50, the control member 40 is inserted into the control member accommodating groove 523 to push the pillar 73 located in the inner space 54 as shown in FIG. 16, making the pillar 73 displace along the slide groove 531 and drive the locking piece 72 to move toward the elastic member 71 along the locking piece accommodating groove 513 to a non-locking position P2 as shown in FIG. 17. In this process, the locking piece 72 elastically compresses the elastic member 71, and the locking part 721 of the locking piece 72 is moved toward the inner space 54 and disengaged from the lock groove 621, such that the convex combining portion 50 and the concave combining portion 60 can be separated from each other. The above-described combining and separating manner for the convex combining portion 50 and the concave combining portion 60 is not only applied between the weight plates 21, but also applied between the adjustable weight unit 20 and the combining member 32 of the handle assembly 30 and between the adjustable weight unit 20 and the positioning member 12 of the base 10. When the first combining portion 211 of the adjustable weight unit 20 is combined with the third combining portion 321 of the handle assembly 30, the locking piece 72 of the first combining portion 211 is located at the locking position Pl and engaged with the lock groove 621 of the third combining portion 321. When the user wants to separate the first combining portion 211 from the third combining portion 321, the user only needs to insert the control member 40 into the first combining portion 211 through its operation opening 522 to move the locking piece 72 of the first combining portion 211 to the non-locking position P2, such that the adjustable weight unit 20 and the handle assembly 30 can be separated. When the second combining portion 212 of the adjustable weight unit 20 is combined with the fourth combining portion 123 of the base 10, the locking piece 72 of the fourth combining portion 123 is located at the locking position Pl and engaged with the lock groove 621 of the second combining portion 212. When the user wants to separate the second combining portion 212 from the fourth combining portion 123, the user only needs to insert the control member 40 into the fourth combining portion 123 through its operation opening 522 to move the locking piece 72 of the fourth combining portion 123 to the non-locking position P2, such that the adjustable weight unit 20 and the base 10 can be separated. In order that the control member 40 can push the locking piece 72 to move smoothly, the control member 40 in this embodiment has a special configuration design. The control member 40 includes a body portion 42, a positioning portion 43 and a driving portion 44, which are downwardly connected in order from the control portion 41. The control portion 41 is shaped as a long sheet, and hollow at the center thereof. The body portion 42 is shaped as an elongated strip. The positioning portion 43 is located at the lower end of the body portion 42, and narrowed in shape with respect to the body portion 42. The driving portion 44 is a cone-shaped sheet. Specifically speaking, the positioning portion 43 is formed with an arc recess 431 at a position which corresponds to the pillar 73 when the control member 40 is inserted in the inner space 54 the convex combining portion 50. After the driving portion 44 of the control member 40 pushes the pillar 73 to displace and the elastic member 71 is compressed simultaneously, when the pillar 73 is located correspondingly to the arc recess 431, the compressed elastic member 71 elastically restores itself to elastically push the pillar 73 to engage with the arc recess 431, and limit the length, for which the locking piece 72 protrudes out of the lock opening 512. For example, the locking piece 72 in this embodiment is limited to not protruding out of the lock opening 512 at all, as shown in FIG. 17. This can also position the control member 40 appropriately to prevent the control member 40 from falling off when in use. Furthermore, in order that the driving portion 44 of the control member 40 can smoothly push the pillar 73 to move, the driving portion 44 of the control member 40 is formed between a terminal end 441 thereof and the arc recess 431 with two guiding bevels 442. In this embodiment, the driving portion 44 of the control member 40 can be provided on only one side thereof, which corresponds to the pillar 73, with the guiding bevel 442, unlimited to having the guiding bevels 442 on both sides. Each of the pillars 73 is cylinder-shaped. After the driving portion 44 of the control member 40 is inserted into the convex combining portion 50 through the operation opening 522 thereof, the guiding bevel 442 of the driving portion 44 gradually pushes the pillar 73 to displace, as shown in FIG. 16. In this way, the pillar 73 can be pushed more reliably, so as to drive the locking piece 72 to move to the non-locking position P2 more reliably. According to the above description, during the operation, the user only needs to pull out and insert the control member 40 to adjust the number of weight plates of each adjustable weight unit 20, thereby adjusting the weight of each adjustable weight unit 20. At first, pull out the control member 40 formerly inserted in the base 10. Then, according to the desired number of weight plates, correspondingly insert the control member 40 into the operation opening 522 of the convex combining portion 50 of one of the weight plates 21. For example, when the user wants the adjustable weight unit 20 combined with each combining member 32 of the handle assembly 30 to have only two weight plates 21, the user inserts the control member 40 in a way as shown in FIG. 14. The control member 40 is inserted into the operation opening 522 and continuously moved to push the pillar 73. The pillar 73 is pushed by the control member 40 to move transversely. The moved pillar 73 drives the locking piece 72 to move together. The moved locking piece 72 pushes the elastic member 71 and elastically compresses it. At the same time, the locking part 721 of the locking piece 72 gradually leaves the lock groove 621. After the locking piece 72 is completely moved out of the lock groove 621, the user can hold the handle 31 to lift up it together with the adjustable weight units 20 combined with the combining members 32 to leave the base 10, such that the user can perform fitness training. For the user, it is effort-saving and time-saving to adjust the weight of the adjustable weight unit 20 by simply pulling out and inserting the control member 40, and it is easier to determine the currently selected weight through the position of the control member 40. In contrast, the conventional technique requires adjusting the switching structures of the weight plates one by one, which is time-consuming and prone to misjudgment, and is too labor-intensive and expensive to repair and maintain. The present invention not only saves time and effort for the user, but also saves time and money on repair and maintenance. Referring to FIG. 18 to FIG. 24, an adjustable dumbbell structure 200 according to a second preferred embodiment of the present invention is a kettlebell. Although the adjustable dumbbell structures 100, 200 of the first and second preferred embodiments are different types of dumbbell structures, they use similar weight plate combining manner. The primary difference between the adjustable dumbbell structure 200 of this embodiment and the first preferred embodiment is that the adjustable dumbbell structure 200 of this embodiment includes only one adjustable weight unit 20, and the inner space 54 of each weight plate 21A in this embodiment is installed with two elastic lock assemblies 70. The structure of this embodiment will be further described hereinafter. The adjustable dumbbell structure 200 includes an adjustable weight unit 20, a handle assembly 30, a control member 40, and a base 80. The adjustable weight unit 20 includes a plurality of weight plates 21A detachably combined in a stacked manner. The adjustable weight unit 20 in this embodiment includes three weight plates 21A, but the amount of the weight plates 21A is unlimited thereto. Each of the weight plates 21A includes a first combining portion 211 and a second combining portion 212, which are located on two sides of the weight plate 21A respectively. For every two adjacent weight plates 21 A, the first combining portion 211 of one of the weight plates is detachably combined with the second combining portion 212 of the other of the weight plates, such that the plurality of weight plates 21A are stacked and combined into the adjustable weight unit 20. The handle assembly 30 includes a handle 31, and a combining member 32 fixed to the handle 31. The handle 31 is curved, and two ends thereof are both fixed to the combining member 32. The combining member 32 includes a base plate 322, and a third combining portion 321. One side of the base plate 322 is monolithically connected with the handle 31. The third combining portion 321 is fastened to another side of the base plate 322 by bolts. The third combining portion 321 is detachably combined with the first combining portion 211 of one of the weight plates 21A of the adjustable weight unit 20. The base 80 includes a bottom plate 81, and a fourth combining portion 82 located on one side of the bottom plate 81. The fourth combining portion 82 is detachably combined with the second combining portion 212 of one of the weight plates 21A of the adjustable weight unit 20. Further speaking, the first combining portion 211 of each of the weight plates 21A is a convex combining portion 50, and the second combining portion 212 of each of the weight plates 21A is a concave combining portion 60. Since the third combining portion 321 of the handle assembly 30 in this embodiment is combined with the first combining portion 211 of one of the weight plates 21A, the third combining portion 321 is the same with the second combining portion 212 of the weight plate 21A. That is, the third combining portion 321 is a concave combining portion 60. Besides, the fourth combining portion 82 of the base 80 in this embodiment is combined with the second combining portion 212 of one of the weight plates 21 A, so the fourth combining portion 82 is the same with the first combining portion 211 of the weight plate 21 A. That is, the fourth combining portion 123 is a convex combining portion 50. However, the present invention can be modified in a way that the third combining portion 321 of the handle assembly 30 is combined with the second combining portion 212 of the weight plate 21 A, and the fourth combining portion 82 of the base 80 is combined with the first combining portion 211 of the weight plate 21 A. In such case, the third combining portion 321 is a convex combining portion 50, and the fourth combining portion 82 is a concave combining portion 60. It can be known from the above description that the adjustable dumbbell structure 200 includes a plurality of convex combining portions 50, and a plurality of concave combining portions 60. The combination between the weight plates 21A, the combination between the weight plate 21A and the combining member 32 of the handle assembly 30, and the combination between the weight plate 21A and the base 80, are all realized through the combination of the convex combining portion 50 with the concave combining portion 60. The technical features and effects in this aspect are similar to those of the first preferred embodiment, but still have some differences in structure. The following description is mainly about the differences. The bottom plate 81 of the base 80 includes an upper board 811 and a lower board 812. The lower board 812 is fixed to one side of the upper board 811. The fourth combining portion 82 is located on another side of the upper board 811. Two temporary storage slots 813 and an access opening 814 communicating with the two temporary storage slots 813 are formed between the upper board 811 and the lower board 812. The control member 40 includes a control portion 41, and two extending portions 45 extending from the control portion 41. The bottom plate 81 of the base 80 is configured for the two extending portions 45 of the control member 40 to be inserted in the two temporary storage slots 813 through the access opening 814, such that the control member 40 is temporarily stored in the bottom plate 81 to be prevented from getting lost. Each of the convex combining portions 50 of the adjustable dumbbell structure 200, i.e. each of the fourth combining portion 82 and the first combining portions 211 in this embodiment, includes a base plate 55, and a first plate 51, a second plate 52 and a third plate 53, which are piled on the base plate 55 in order and fastened by bolts. The first plate 51, the second plate 52 and the third plate 53 are similar in function to those in the first preferred embodiment, which are stacked to form the inner space 54. However, the first plate 51 in this embodiment has two lock openings 512 toward opposite directions, and two locking piece accommodating grooves 513 communicating with the two lock openings 512 respectively, and is installed therein with two elastic lock assemblies 70. Only one of the lock openings 512 located on one side of the convex combining portion 50 is shown in FIG. 20. The opposite side has the other lock opening 512. The locking pieces 72 of the two elastic lock assemblies 70 are disposed in the two locking piece accommodating grooves 513 respectively. The second plate 52 in this embodiment is composed of three elongated boards 524 disposed at intervals, thereby formed therebetween with two operation openings 522, and two control member accommodating grooves 523 communicating with the two operation openings 522 respectively, for the two extending portions 45 of the control member 40 to be inserted in the two control member accommodating grooves 523 through the two operation openings 522 respectively to push the pillars 73 of the two elastic lock assemblies 70 respectively. However, in the condition that each weight plate has two elastic lock assemblies 70, the weight plate can be still provided with only one operation opening 522 and only one control member accommodating groove 523, as long as the control member 40 inserted into the control member accommodating groove 523 can push the pillars 73 of the two elastic lock assemblies 70 at the same time. The third plate 53 has two slide grooves 531. The pillars 73 of the two elastic lock assemblies 70 are slidably disposed in the two slide grooves 531 respectively. It should be mentioned that the convex combining portion 50 in the present invention is unlimited to having the slide groove 531, as long as there is another mechanism for restricting the elastic lock assembly 70 in the inner space 54. For example, the control member accommodating groove 523 may be configured to restrict the position of the pillar 73. However, the slide groove 531 can control the position of the pillar 73 and the locking piece 72 more precisely, making the locking relationship and non-locking relationship between the convex combining portion 50 and the concave combining portion 60 more reliable. The elastic lock assembly 70 in this embodiment is primarily different from that in the first preferred embodiment in that every elastic lock assembly 70 includes two elastic members 71, and the inner surface of the inner space 54 is correspondingly recessed with two positionally limiting parts 514 in the locking piece accommodating groove 513. The locking piece 72 is also correspondingly recessed with two positionally limiting parts 722. The first end 711 and the second end 712 of each of the elastic members 71 are accommodated in the positionally limiting part 514 in the locking piece accommodating groove 513 and the positionally limiting part 722 of the locking piece 72 respectively, and elastically pressed on the inner surfaces thereof. However, in the present invention, the amount of the elastic member 71 of the elastic lock assembly 70 is unlimited. Different numbers of elastic members 71 can be set according to different design requirements. Each of the concave combining portions 60 of the adjustable dumbbell structure 200, i.e. each of the third combining portion 321 and the second combining portions 212 in this embodiment, is similar to that in the first preferred embodiment, but the primary difference therebetween is that the concave combining portion 60 in this embodiment includes two lock grooves 621 facing each other. That is, the two lock grooves 621 are toward opposite directions. The plurality of weight plates 21A of the adjustable weight unit 20 are combined in a stacked manner through the combination of the convex combining portion 50 with the concave combining portion 60, and the convex combining portion 50 of one of the weight plates 21A is combined with the concave combining portion 60 of the handle assembly 30. Furthermore, the concave combining portion 60 of another weight plate 21A of the adjustable weight unit 20 is combined with the convex combining portion 50 of the base 80. The convex combining portions 50 are combined with the concave combining portions 60 in a way that the two locking pieces 72 of each of the convex combining portions 50 are engaged with the two lock grooves 621 of the associated concave combining portion 60 respectively, that will be specified hereinafter. As shown in FIG. 23 and FIG. 24, the two locking pieces 72 in each of the convex combining portions 50 can be controlled by the control member 40 inserted into the inner space 54 through the operation opening 522 at the same time, thereby switched between a locking position Pl and a non-locking position P2, and the two locking pieces 72 are moved in opposite directions. That is, when the two locking pieces 72 are moved from their respective locking positions Pl to their respective non-locking positions P2, the two locking pieces 72 are moved to approach each other; when the two locking pieces 72 are moved from their respective non-locking positions P2 to their respective locking positions Pl, the two locking pieces 72 are moved away from each other. When the locking piece 72 is located at the locking position Pl, a locking part 721 of the locking piece 72 protrudes out of the lock opening 512. When one of the convex combining portions 50 and one of the concave combining portions 60 are combined with each other, the locking piece 72 of the convex combining portion 50 is elastically pushed by the elastic member 71, thereby normally located at the locking position Pl and engaged with the lock groove 621 of the concave combining portion 60. At this time, the convex combining portion 50 and the concave combining portion 60 are engaged with each other firmly and reliably. After the user inserts the control member 40 into the operation opening 522 of anyone of the convex combining portions 50, the control member 40 pushes the pillars 73 of the two elastic lock assemblies 70 located in the inner space 54, making the locking pieces 72 of the two elastic lock assemblies 70 moved in opposite directions to their respective non-locking positions P2 and disengaged from the lock grooves 621, such that the convex combining portion 50 and the concave combining portion 60 can be separated from each other. The above-described combining and separating manner for the convex combining portion 50 and the concave combining portion 60 is not only applied between the weight plates 21 A, but also applied between the weight plate 21A of the adjustable weight unit 20 and the combining member 32 of the handle assembly 30 and between the weight plate 21A of the adjustable weight unit 20 and the base 80. The control member 40 in this embodiment also has the configuration design for pushing the locking piece 72 to move more smoothly, that is similar to that in the first preferred embodiment. As shown in FIG. 23, each extending portion 45 of the control member 40 includes a body portion 42, a positioning portion 43 and a driving portion 44, which are connected in order from the control portion 41. The driving portion 44 has a guiding bevel 442. The positioning portion 43 has an arc recess 431. After the driving portion 44 of the control member 40 is inserted into the operation opening 522, the guiding bevel 442 of the driving portion 44 gradually pushes the pillar 73 to displace. In this way, the pillar 73 can be pushed more reliably, so as to drive the locking piece 72 to move to the non-locking position P2 more reliably. When the two pillars 73 are located correspondingly to the arc recesses 431, the compressed elastic members 71 elastically restore themselves to elastically push the two pillars 73 to engage with the arc recesses 431, and limit the lengths, for which the two locking pieces 72 protrude out of the two lock openings 512. This can also position the control member 40 appropriately to prevent the control member 40 from falling off when in use. As a result, the user only needs to pull out and insert the control member 40 to quickly remove a part of the weight plates 21A of the adjustable dumbbell structure 200 or add more weight plates 21A, so as to adjust the weight of the adjustable weight unit 20. Such adjusting manner is effort-saving and time-saving, and makes it easier to determine the currently selected weight through the position of the control member 40. Besides, the structure of the present invention is not overly complex, so it can save time and money on repair and maintenance. No matter in the type with two adjustable weight units 20 according to the first preferred embodiment or the type with only one adjustable weight unit 20 according to the second preferred embodiment, the locking mechanism between the convex combining portion 50 and the concave combining portion 60 is unlimited to that provided in the aforementioned embodiments. It is only required that the convex combining portion 50 includes an inner space 54, a locking piece 72 disposed in the inner space 54, and an operation opening 522 and a lock opening 512, which communicate with the inner space 54, the concave combining portion 60 includes a lock groove 621 which can be engaged with the locking piece 72 located at the locking position Pl, and the convex combining portion 50 is configured for a control member 40 to be inserted in the inner space 54 through the operation opening 522 to switch the locking piece 72 between the locking position Pl and the non-locking position P2. The following third to fifth preferred embodiments are instanced, which use different locking mechanisms to achieve similar effects to the first and second preferred embodiments. It should be mentioned here that in the above-described first and second preferred embodiments, the control member 40 is inserted into the inner space 54 through the operation opening 522 of the convex combining portion 50 only when required to be operated. However, in the following third to fifth preferred embodiments, the control member is disposed in the inner space 54, without being removed. Therefore, every convex combining portion 50 is installed with a control member. When it is mentioned in the present invention that the control member is inserted in the inner space through the operation opening, it includes the case that the control member is inserted into the inner space through the operation opening only when required to be operated, and also includes the case that the control member is kept inserted in the inner space. Referring to FIG. 25 to FIG. 29, a weight plate 2IB and a control member 40 according to the third preferred embodiment of the present invention are shown for illustrating the locking mechanism between the convex combining portion 50 and the concave combining portion 60 of this embodiment. This locking mechanism is applicable between the weight plates 2IB, between the weight plate 2IB and a base 10 or base 80 as described above, and between the weight plate 21B and a handle assembly 30 as described above. The weight plate 2IB in this embodiment is similar to that in the first preferred embodiment, but has a primary difference that the control member 40 is disposed in the control member accommodating groove 523 in a way that the control member 40 is switchable between a retraction position P3 and a reach-out position P4 by being linearly moved by a user. Besides, the control member 40 includes an oblique guiding groove 46 and two positioning holes 47, 48. The first plate 51 of the convex combining portion 50 is correspondingly provided with a positioning pillar 515. Furthermore, the locking piece 72 is only fixed with the pillar 73, but not connected with any elastic member. The pillar 73 is inserted through the oblique guiding groove 46 and the control member accommodating groove 523, and inserted into the slide groove 531 of the third plate 53. When the control member 40 is located at the retraction position P3, the positioning pillar 515 is located in the positioning hole 47, the pillar 73 is located at an upper end 461 of the oblique guiding groove 46, and the locking piece 72 is located at the locking position Pl. That is, at this time, the locking part 721 of the locking piece 72 protrudes out of the lock opening 512, and can be engaged with the lock groove 621 of the concave combining portion 60. When the user pulls the control member 40 upwardly, the positioning pillar 515 leaves the positioning hole 47, the control member 40 slides along the control member accommodating groove 523 upwardly, and the pillar 73 is pushed by the inner wall of the oblique guiding groove 46 to slide along the oblique guiding groove 46 and slide along the slide groove 531 to drive the locking piece 72 to slide along the locking piece accommodating groove 513, making the locking part 721 of the locking piece 72 gradually moved toward the inner space 54. When the control member 40 is located at the reach-out position P4, the positioning pillar 515 is located in the positioning hole 48, the pillar 73 is located at a lower end 462 of the oblique guiding groove 46, and the locking piece 72 is located at the non-locking position P2. That is, at this time, the locking part 721 of the locking piece 72 is retracted into the inner space 54 without being engaged with the lock groove 621 of the concave combining portion 60. As a result, the locking mechanism between the convex combining portion 50 and the concave combining portion 60 in this embodiment allows the user to use only a simple action of linearly moving the control member 40, i.e. pulling upwardly or inserting downwardly, to switch the locking piece 72 between the locking position Pl and the nonlocking position P2. Therefore, the user can quickly and conveniently adjust the number of the weight plates of the dumbbell to make the weight of the dumbbell meet the need of the user. Besides, the structure of the present invention is not overly complex, so it can save time and money for repair and maintenance. Referring to FIG. 30 to FIG. 35, a weight plate 21C and a control member 40 according to a fourth preferred embodiment of the present invention are shown for illustrating the locking mechanism between the convex combining portion 50 and the concave combining portion 60 of this embodiment. This locking mechanism is applicable between the weight plates 2IC, between the weight plate 21C and a base 10 or base 80 as described above, and between the weight plate 21C and a handle assembly 30 as described above. The weight plate 21C in this embodiment is similar to that in the first preferred embodiment, but has a primary difference that the first plate 51 of the convex combining portion 50 has two lock openings 512 toward opposite directions, and two locking piece accommodating grooves 513 communicating with the two lock openings 512 respectively. Each locking piece accommodating groove 513 is installed therein with a locking piece 72. Each locking piece 72 is fixed with a pillar 73. The front plate 62 of the concave combining portion 60 is correspondingly provided with lock grooves 621 which can be engaged with the two locking pieces 72. Furthermore, the first plate 51 is provided thereon with a pivot axle 516. The control member 40 is correspondingly provided with a pivot hole 49. The pivot axle 516 is inserted in the pivot hole 49, so that the control member 40 is disposed in the control member accommodating groove 523 in a way that the control member 40 is switchable between a first angular position P5 and a second angular position P6 by being swung by a user. In addition, the control member 40 includes two oblique guiding grooves 46 located on two opposite sides of the pivot hole 49 respectively. The two pillars 73 are disposed in the two oblique guiding grooves 46 respectively. When the control member 40 is located at the first angular position P5, the control portion 41 of the control member 40 at the topmost end thereof is deflected to one side of the operation opening 522, and the two locking pieces 72 are located at their respective locking positions Pl. That is, at this time, the locking parts 721 of the two locking pieces 72 protrude out of the two lock openings 512, and can be engaged with the lock grooves 621 of the concave combining portion 60. When the user pushes the control portion 41 of the control member 40 to the other side of the operation opening 522, the two pillars 73 are pushed by the inner walls of the two oblique guiding grooves 46 to move in opposite directions and slightly slide in the oblique guiding grooves 46 to drive the two locking pieces 72 to slide in opposite directions along the two locking piece accommodating grooves 513, making the locking parts 721 of the two locking pieces 72 gradually moved toward the inner space 54. When the control member 40 is located at the second angular position P6, the two locking pieces 72 are located at their respective non-locking positions P2. That is, at this time, the locking parts 721 of the two locking pieces 72 are retracted into the inner space 54 without being engaged with the lock grooves 621 of the concave combining portion 60. As a result, the locking mechanism between the convex combining portion 50 and the concave combining portion 60 in this embodiment allows the user to use only a simple action of swinging the control member 40 to switch the two locking pieces 72 between the locking position Pl and the non-locking position P2. Therefore, the user can quickly and conveniently adjust the number of the weight plates of the dumbbell to make the weight of the dumbbell meet the need of the user. Besides, the structure of the present invention is not overly complex, so it can save time and money for repair and maintenance. Referring to FIG. 36 to FIG. 40, a weight plate 21D and a control member 90 according to a fifth preferred embodiment of the present invention are shown for illustrating the locking mechanism between the convex combining portion 50 and the concave combining portion 60 of this embodiment. This locking mechanism is applicable between the weight plates 2ID, between the weight plate 2ID and a base 10 or base 80 as described above, and between the weight plate 21D and a handle assembly 30 as described above. The weight plate 2ID in this embodiment is similar to that in the first preferred embodiment, but has a primary difference that the convex combining portion 50 includes two first plates 51 disposed on two sides of the second plate 52 respectively. The two first plates 51 are opposite in shape in the left and right direction, so the convex combining portion 50 includes two lock openings 512 toward opposite directions, and two locking piece accommodating grooves 513 communicating with the two lock openings 512 respectively. Each locking piece accommodating groove 513 is installed therein with a locking piece 72. However, there may be only one first plate 51 and only one locking piece 72 in this embodiment. Besides, the control member 40 in each above embodiment is configured to indirectly drive the locking piece 72 to move through the pillar 73, but the control member 90 in this embodiment is configured to be rotated by the user to directly drive the locking piece 72 to move. The control member 90 is provided at the lowest end thereof with a gear portion 91. Each of the locking pieces 72 is correspondingly provided with a rack portion 723. The rack portions 723 of the two locking pieces 72 are engaged with the gear portion 91 of the control member 90. The second plate 52 is provided with a control member accommodating groove 523 corresponding in shape to the control member 90 and the locking pieces 72 for the control member 90 to be rotatably disposed in the control member accommodating groove 523. When the control member 90 is rotated, the gear portion 91 drives the two locking pieces 72 to move in opposite directions between their respective locking positions Pl and nonlocking positions P2. When the two locking pieces 72 are located at their locking positions Pl, the locking parts 721 of the two locking pieces 72 protrude out of the two lock openings 512, and can be engaged with the lock grooves 621 of the concave combining portion 60. When the two locking pieces 72 are located at their non-locking positions P2, the locking parts 721 of the two locking pieces 72 are retracted into the inner space 54 without being engaged with the lock grooves 621 of the concave combining portion 60. As a result, the locking mechanism between the convex combining portion 50 and the concave combining portion 60 in this embodiment allows the user to use only a simple action of rotating the control member 90 to switch the two locking pieces 72 between the locking position Pl and the non-locking position P2. Therefore, the user can quickly and conveniently adjust the number of the weight plates of the dumbbell to make the weight of the dumbbell meet the need of the user. Besides, the structure of the present invention is not overly complex, so it can save time and money for repair and maintenance. Summarizing the above embodiments, the present invention provides a weight plate unlocking method for an adjustable dumbbell structure, which includes the following steps. Provide an adjustable dumbbell structure, such as, but unlimited to, the type according to the first or second preferred embodiment. The adjustable dumbbell structure includes a plurality of weight plates detachably combined in a stacked manner, such as, but unlimited to, the weight plates 21, 21A-21D in the first to fifth preferred embodiments. Each of the weight plates includes a concave combining portion 60 and a convex combining portion 50, which are located on two sides of the weight plate respectively. The concave combining portion 60 includes a lock groove 621, or may include a plurality of lock grooves 621. The convex combining portion 50 includes an inner space 54, a locking piece 72 (or a plurality of locking pieces 72) disposed in the inner space 54, and an operation opening 522 and a lock opening 512 (or a plurality of lock openings 512), which communicate with the inner space 54. For every two adjacent weight plates, the convex combining portion 50 of one of the weight plates is detachably combined with the concave combining portion 60 of the other of the weight plates in a way that a locking part 721 of the locking piece 72 of the convex combining portion 50 protrudes out of the lock opening 512, and is engaged with the lock groove 621 of the concave combining portion 60. Provide a control member, such as, but unlimited to, the control member 40, 90 in the first to fifth preferred embodiments, and make the control member inserted in the inner space 54 through the operation opening 522 of one of the weight plates, and directly or indirectly connected with the locking piece 72. For example, the control member 90 in the fifth preferred embodiment is directly connected with the locking piece 72, and the control member 40 in the first to fourth preferred embodiments is indirectly connected with the locking piece 72. The control member may be inserted into the inner space 54 when required to be used, or kept inserted in the inner space 54. 5 Use the control member to move the locking piece 72, making the locking part 721 of the locking piece 72 moved toward the inner space 54 to be disengaged from the lock groove 621. By the weight plate unlocking method for the adjustable dumbbell structure provided by the present invention, the user can quickly and conveniently adjust the 10 number of the weight plates of the dumbbell to make the weight of the dumbbell meet the need of the user. Even if the weight is not suitable, it can be quickly adjusted again, thereby saving the adjustment time. Besides, the dumbbell is prevented from overly complex mechanisms and the resulting drawback of high maintenance and repair costs. The invention being thus described, it will be obvious that the same may be 15 varied in many ways. Such variations are not to be regarded as a departure from the scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims

1. An adjustable dumbbell structure comprising:at least one adjustable weight unit, the adjustable weight unit comprising a plurality of weight plates, the weight plates being detachably combined in a stacked manner, each of the weight plates comprising a first combining portion and a second combining portion, the first combining portion and the second combining portion being located on two sides of the weight plate respectively, for every two adjacent said weight plates, the first combining portion of one of the weight plates being detachably combined with the second combining portion of the other of the weight plates;a handle assembly comprising a handle, and at least one combining member fixed to the handle, the combining member comprising a third combining portion, the third combining portion being detachably combined with one of the first combining portion and the second combining portion of one of the weight plates of the adjustable weight unit; andat least one control member;wherein the adjustable dumbbell structure comprises a plurality of concave combining portions and a plurality of convex combining portions; each of the concave combining portions comprises at least one lock groove; each of the convex combining portions comprises an inner space, at least one locking piece disposed in the inner space, and at least one operation opening and at least one lock opening, which communicate with the inner space; the locking piece comprises a locking part; the locking piece is switchable between a locking position and a non-locking position by being controlled by the control member which is inserted in the inner space through the operation opening; the first combining portion of each of the weight plates is said convex combining portion; the second combining portion of each of the weight plates is said concave combiningportion; the third combining portion of the handle assembly is one of said convex combining portion and said concave combining portion; when one of the convex combining portions is combined with one of the concave combining portions, the locking piece of the convex combining portion is located at the locking position, and the locking part of the locking piece protrudes out of the lock opening, and is engaged with the lock groove of the concave combining portion; when the locking piece is switched to the nonlocking position, the locking part is moved toward the inner space and disengaged from the lock groove.

2. The adjustable dumbbell structure as claimed in claim 1, wherein the third combining portion of the combining member of the handle assembly is said concave combining portion for the locking piece of one of the first combining portions of the adjustable weight unit to be engaged with the lock groove of the third combining portion when the locking piece is located at the locking position.

3. The adjustable dumbbell structure as claimed in claim 1, wherein the adjustable dumbbell structure comprises two said adjustable weight units; the handle assembly comprises two said combining members; the two combining members are fixed to two ends of the handle respectively; the two adjustable weight units are detachably combined with the third combining portions of the two combining members respectively.

4. The adjustable dumbbell structure as claimed in claim 3, wherein the adjustable dumbbell structure further comprises a base; the base comprises a frame and two positioning members; the frame comprises two inside surfaces facing each other; the two positioning members are fixed to the two inside surfaces respectively; each of thepositioning members comprises a fourth combining portion; the fourth combining portions of the two positioning members face each other, and are detachably combined with the two adjustable weight units respectively; each of the fourth combining portions is one of said convex combining portion and said concave combining portion.

5. The adjustable dumbbell structure as claimed in claim 4, wherein the fourth combining portion of each of the positioning members of the base is said convex combining portion for the lock groove of one of the second combining portions of each of the adjustable weight units to be engaged with the locking piece of the fourth combining portion located at the locking position; the third combining portion of each of the combining members of the handle assembly is said concave combining portion for the locking piece of one of the first combining portions of each of the adjustable weight units to be engaged with the lock groove of the third combining portion when the locking piece is located at the locking position.

6. The adjustable dumbbell structure as claimed in claim 4, wherein each of the positioning members of the base comprises an outer piece and a blocking piece; the outer piece is fixed to one side of the blocking piece; the fourth combining portion is fixed to another side of the blocking piece; a temporary storage space and an access opening communicating with the temporary storage space are formed between the outer piece and the blocking piece for the control member to be inserted into the temporary storage space through the access opening for temporary storage.

7. The adjustable dumbbell structure as claimed in claim 6, wherein the outer piece comprises an inner side and an outer side opposite to the inner side; the inner sideis fixed to the blocking piece; the outer side is recessed with a connecting groove; the frame comprises two frame plates; each of the frame plates comprises an extending section, and two connecting sections perpendicularly extending from two ends of the extending section respectively; the two connecting sections of each of the frame plates are connected to the connecting grooves of the outer pieces of the two positioning members respectively.

8. The adjustable dumbbell structure as claimed in claim 6, wherein the outer piece is further formed with a buckle recess located correspondingly to the temporary storage space and the access opening, and an engaging rib protruding from each of two side walls of the buckle recess; the control member has a plurality of arc engaging recesses; when the control member is inserted in the temporary storage space through the access opening, the control member is partially exposed in the buckle recess, and the arc engaging recesses are engaged with the engaging ribs and positioned.

9. The adjustable dumbbell structure as claimed in claim 1, wherein the adjustable dumbbell structure comprises only one said adjustable weight unit; the handle assembly comprises only one said combining member; the handle is curved, and two ends of the handle are both fixed to the combining member.

10. The adjustable dumbbell structure as claimed in claim 9, wherein the adjustable dumbbell structure further comprises a base; the base comprises a fourth combining portion; the fourth combining portion of the base is detachably combined with one of the first combining portion and the second combining portion of one of the weight plates of the adjustable weight unit; the fourth combining portion is one of said convexcombining portion and said concave combining portion.

11. The adjustable dumbbell structure as claimed in claim 10, wherein the fourth combining portion of the base is said convex combining portion for the lock groove of one of the second combining portions of the adjustable weight unit to be engaged with the locking piece of the fourth combining portion located at the locking position; the third combining portion of the combining member of the handle assembly is said concave combining portion for the locking piece of one of the first combining portions of the adjustable weight unit to be engaged with the lock groove of the third combining portion when the locking piece is located at the locking position.

12. The adjustable dumbbell structure as claimed in claim 10, wherein the base comprises a bottom plate; the bottom plate comprises an upper board and a lower board; the lower board is fixed to one side of the upper board; the fourth combining portion is located at another side of the upper board; at least one temporary storage slot and an access opening communicating with the temporary storage slot are formed between the upper board and the lower board for the control member to be inserted into the temporary storage slot through the access opening for temporary storage.

13. The adjustable dumbbell structure as claimed in claim 1, wherein the adjustable dumbbell structure comprises a plurality of elastic lock assemblies; each of the convex combining portions is provided in the inner space thereof with at least one said elastic lock assembly; each of the elastic lock assemblies comprises an elastic member, a said locking piece, and a pillar; the elastic member comprises a first end and a second end; the first end is attached to an inner surface of the inner space; the second end isattached to an end of the locking piece; the locking part of the locking piece is located at another end of the locking piece; the locking piece is elastically pushed by the elastic member to be normally located at the locking position; the pillar is attached to one side of the locking piece, and located correspondingly to the operation opening; the control member is detachably inserted in the inner space of anyone of the convex combining portions; after the control member is inserted into the operation opening of anyone of the convex combining portions, the control member pushes the pillar located in the inner space, making the pushed pillar drive the locking piece to move to the non-locking position and elastically compress the elastic member.

14. The adjustable dumbbell structure as claimed in claim 13, wherein each of the concave combining portions comprises two said lock grooves toward opposite directions; each of the convex combining portions comprises two said lock openings toward opposite directions, and two locking piece accommodating grooves communicating with the two lock openings respectively; each of the convex combining portions is provided in the inner space thereof with two said elastic lock assemblies; the locking pieces of the two elastic lock assemblies are disposed in the two locking piece accommodating grooves respectively; when the control member is inserted into the operation opening of anyone of the convex combining portions, the control member pushes the pillars of the two elastic lock assemblies located in the inner space to move the locking pieces of the two elastic lock assemblies in opposite directions to their respective non-locking positions.

15. The adjustable dumbbell structure as claimed in claim 14, wherein the control member comprises a control portion, and two extending portions extending fromthe control portion; each of the convex combining portions comprises two said operation openings, and two control member accommodating grooves communicating with the two operation openings respectively; when the control member is inserted into anyone of the convex combining portions, the two extending portions are inserted into the two control member accommodating grooves through the two operation openings respectively, so as to push the pillars of the two elastic lock assemblies respectively.

16. The adjustable dumbbell structure as claimed in claim 13, wherein each of the convex combining portions comprises a first plate, a second plate, and a third plate; the first plate, the second plate and the third plate are stacked to form the inner space; the first plate comprises a locking piece accommodating groove formed in a transversely recessed manner, and a positionally limiting part located in the locking piece accommodating groove; the second plate comprises a control member accommodating groove formed in a vertically recessed manner; the third plate comprises a slide groove extending transversely; the first ends of the elastic members of the elastic lock assemblies are attached to the positionally limiting parts of the first plates of the convex combining portions; the pillars of the elastic lock assemblies are slidably disposed in the slide grooves of the third plates of the convex combining portions; after being inserted into the operation opening of anyone of the convex combining portions, the control member is inserted into the control member accommodating groove of the second plate to push the pillar, making the pillar displace along the slide groove of the third plate and drive the locking piece to move toward the elastic member and compress the elastic member, and meanwhile disengage the locking piece from the lock groove.

17. The adjustable dumbbell structure as claimed in claim 13, wherein thecontrol member comprises a control portion, a body portion, a positioning portion and a driving portion, which are connected in order; the positioning portion is formed with an arc recess at a position which corresponds to the pillar when the control member is inserted in the inner space of the convex combining portion; after the control member pushes the pillar to displace by the driving portion and the elastic member is compressed simultaneously, when the pillar is located correspondingly to the arc recess, the compressed elastic member elastically restores itself to elastically push the pillar to engage with the arc recess, and limit a length, for which the locking piece protrudes out of the lock opening.

18. The adjustable dumbbell structure as claimed in claim 17, wherein the driving portion of the control member is formed between a terminal end thereof and the arc recess with a guiding bevel; each of the pillars is cylinder-shaped; after the driving portion of the control member is inserted into the operation opening of the convex combining portion, the guiding bevel of the driving portion gradually pushes the pillar to displace.

19. The adjustable dumbbell structure as claimed in claim 1, wherein the adjustable dumbbell structure comprises:a base comprising a frame and two positioning members, the frame comprising two inside surfaces facing each other, the two positioning members being disposed on the two inside surfaces respectively, each of the positioning members comprising a fourth combining portion, the fourth combining portions of the two positioning members facing each other and being said convex combining portions;two said adjustable weight units detachably combined with the two positioningmembers of the base respectively, the second combining portion of one of the weight plates of each of the adjustable weight units being detachably combined with the fourth combining portion of the associated positioning member;the handle assembly comprising the handle, and two said combining members combined to two ends of the handle respectively, the two adjustable weight units being detachably combined with the two combining members respectively, the third combining portion of each of the combining members being said concave combining portion, and detachably combined with the first combining portion of one of the weight plates of the associated adjustable weight unit;a plurality of elastic lock assemblies disposed in the inner spaces of the convex combining portions respectively, each of the elastic lock assemblies comprising an elastic member, a said locking piece, and a pillar, the elastic member comprising a first end and a second end, the first end being elastically pressed on an inner surface of the inner space, the second end being attached to an end of the locking piece, the locking part of the locking piece being located at another end of the locking piece, and elastically pushed by the elastic member to normally protrude out of the lock opening and be engaged with the lock groove of the concave combining portion, the pillar being attached to one side of the locking piece and located correspondingly to the operation opening; andthe control member detachably inserted in the inner space of anyone of the convex combining portions, after the control member is inserted into the operation opening of anyone of the convex combining portions, the control member pushing the pillar located in the inner space, making the pushed pillar drive the locking piece to elastically compress the elastic member, and meanwhile disengage the locking piece from the lock groove.

20. The adjustable dumbbell structure as claimed in claim 1, wherein each of the concave combining portions comprises a main plate, two front plates, and two rear plates; the two rear plates are fixed to one side of the main plate; the two front plates are piled on the two rear plates respectively; an assembling groove is formed between the main plate, the two front plates and the two rear plates; at least one of the front plates is formed on one side thereof toward the assembling groove with the lock groove; the convex combining portions are detachably combined to the assembling grooves.

21. The adjustable dumbbell structure as claimed in claim 1, wherein each of the convex combining portions comprises a locking piece accommodating groove and a control member accommodating groove; the locking piece accommodating groove communicates with the lock opening; the locking piece is disposed in the locking piece accommodating groove, and slides between the locking position and the non-locking position along the locking piece accommodating groove; the control member accommodating groove communicates with the operation opening for the control member to be disposed in the control member accommodating groove.

22. The adjustable dumbbell structure as claimed in claim 21, wherein each of the convex combining portions comprises a first plate, a second plate, and a third plate; the first plate, the second plate and the third plate are stacked to form the inner space; the lock opening is formed on an outer edge of the first plate; the locking piece accommodating groove extends from the lock opening into the first plate in a first direction; the operation opening is formed on an outer edge of the second plate; the control member accommodating groove extends from the operation opening into the second plate in a second direction; the first direction and the second direction are perpendicular to eachother.

23. The adjustable dumbbell structure as claimed in claim 21, wherein the adjustable dumbbell structure comprises a plurality of said control members; each of the convex combining portions is installed with a said control member; the control member is disposed in the control member accommodating groove in a way that the control member is switchable between a retraction position and a reach-out position by being linearly moved by a user; the control member comprises an oblique guiding groove; a pillar is fixed on the locking piece; the pillar is disposed in the oblique guiding groove; when the control member is switched between the retraction position and the reach-out position, the control member pushes the pillar to slide along the oblique guiding groove to drive the locking piece to switch between the locking position and the non-locking position.

24. The adjustable dumbbell structure as claimed in claim 21, wherein the adjustable dumbbell structure comprises a plurality of said control members; each of the convex combining portions is installed with a said control member; the control member is disposed in the control member accommodating groove in a way that the control member is switchable between a first angular position and a second angular position by being swung by a user; the control member comprises an oblique guiding groove; a pillar is fixed on the locking piece; the pillar is disposed in the oblique guiding groove; when the control member is switched between the first angular position and the second angular position, the control member pushes the pillar to move, driving the locking piece to switch between the locking position and the non-locking position.

25. The adjustable dumbbell structure as claimed in claim 24, wherein each of the convex combining portions comprises two said lock openings toward opposite directions, two said locking piece accommodating grooves communicating with the two lock openings respectively, two said locking pieces disposed in the two locking piece accommodating grooves respectively, and two said pillars attached to the two locking pieces respectively; the control member comprises two said oblique guiding grooves; the two pillars are disposed in the two oblique guiding grooves respectively; when the control member is switched between the first angular position and the second angular position, the control member pushes the two pillars to move, driving the two locking pieces to move in opposite directions to switch between the locking position and the non-locking position.

26. The adjustable dumbbell structure as claimed in claim 21, wherein the adjustable dumbbell structure comprises a plurality of said control members; each of the convex combining portions is installed with a said control member; the control member is disposed in the control member accommodating groove rotatably by a user; the control member comprises a gear portion; the locking piece comprises a rack portion; the rack portion is engaged with the gear portion; when the control member is rotated, the gear portion drives the locking piece to move between the locking position and the non-locking position.

27. The adjustable dumbbell structure as claimed in claim 26, wherein each of the convex combining portions comprises two said lock openings toward opposite directions, two said locking piece accommodating grooves communicating with the two lock openings respectively, and two said locking pieces disposed in the two locking pieceaccommodating grooves respectively; the rack portions of the two locking pieces are engaged with the gear portion of the control member; when the control member is rotated, the gear portion drives the two locking pieces to move in opposite directions between the locking position and the non-locking position.

28. A weight plate of an adjustable dumbbell structure, which is adapted to be unlocked by a control member, the weight plate comprising a concave combining portion and a convex combining portion, the concave combining portion and the convex combining portion being located on two sides of the weight plate respectively, the concave combining portion comprising a lock groove, the convex combining portion comprising an inner space, a locking piece disposed in the inner space, and an operation opening and a lock opening, which communicate with the inner space, the locking piece comprising a locking part, the locking piece being switchable between a locking position and a non-locking position by being controlled by the control member which is inserted in the inner space through the operation opening, when the locking piece of the convex combining portion is located at the locking position, the locking part of the locking piece protruding out of the lock opening for being engaged with the lock groove of the concave combining portion of another said weight plate, when the locking piece of the convex combining portion is switched from the locking position to the non-locking position, the locking part of the locking piece being moved toward the inner space for being disengaged from the lock groove.

29. A weight plate unlocking method for an adjustable dumbbell structure, the weight plate unlocking method comprising the steps of:providing an adjustable dumbbell structure, the adjustable dumbbell structurecomprising a plurality of weight plates, the weight plates being detachably combined in a stacked manner, each of the weight plates comprising a concave combining portion and a convex combining portion, the concave combining portion and the convex combining portion being located on two sides of the weight plate respectively, the concave5 combining portion comprising a lock groove, the convex combining portion comprising an inner space, a locking piece disposed in the inner space, and an operation opening and a lock opening, which communicate with the inner space, for every two adjacent said weight plates, the convex combining portion of one of the weight plates being detachably combined with the concave combining portion of the other of the weight plates in a way10 that a locking part of the locking piece of the convex combining portion protrudes out of the lock opening, and is engaged with the lock groove of the concave combining portion;providing a control member, and making the control member inserted in the inner space through the operation opening of one of the weight plates and directly or indirectly connected with the locking piece; and15 using the control member to move the locking piece, making the locking partof the locking piece moved toward the inner space to be disengaged from the lock groove.A

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