Adjustable dumbbell

1. A weight-adjustable dumbbell, comprising a handle bar having a middle section and two end sections, a handle, two weight plate holders, two pin cartridges, a plurality of weight plates and a base; the handle being concentrically and rotatably installed on the middle section of the handle bar, each of the two weight plate holders being fixedly attached to a respective one of the two end sections of the handle bar; each of the two pin cartridges being removably hosted inside a respective one of the two weight plate holders; each of the plurality of weight plates being detachably connected to either of the two weight plate holders or disconnected from either of the two weight plate holders and removably rested on the base; where:

each of the two pin cartridges comprises a plurality of pins and each of the plurality of pins comprises a pin head and a pin bottom, and each of the plurality of pins independently assumes a normal position or an extended position and independently changes between the two positions by a lateral translocation;

each of the plurality pins is corresponding to one of the plurality of weight plates in that when a pin assumes an extended position a corresponding weight plate of the plurality of weight plates is locked to one of the two weight plate holders; and

as a way of adjusting the dumbbell weight, a rotation of the handle bar to a predefined position relative to the two weight plate holders causes the lateral translocation of one or more of the plurality of pins so that at least one pin of the plurality of pins changes from the normal position to the extended position and/or at least one pin of the plurality of pins changes from the extended position to the normal position to result in a different set of pins of the plurality of pins being in the extended position and hence a different set of weight plates of the plurality of weight plates being attached to the two weight plate holders.

2. The weight-adjustable dumbbell according to claim 1 , wherein the two pin cartridges each assume two states, a closed state and an open state, and in the open state, all of the plurality of pins assume the normal position and the handle bar is allowed to rotate relative to the two weight plate holders, while in the closed state one or more of the plurality of pins assumes the extended position, thereby preventing the rotation of the handle bar relative to the two weight plate holders and at the same time locking one or more of the plurality of weight plates to one of the two weight plate holders.

3. The weight-adjustable dumbbell according to claim 2 , wherein the handle has two ends and each of the two ends comprises a support plate and a circular locating plate, which are fixedly connected to the handle and thus concentrically rotatable together with the handle relative to the two weight plate holders;

the circular locating plate comprises a plurality of fan-shaped sectors, each of the plurality of fan-shaped sectors having a plurality of holes, and each of the plurality of holes capable of receiving one pin head of the plurality of pins extending out of one of the two weight plate holders; and

with the two pin cartridges in the open state inside the two weight plate holders, none of the plurality of holes of the circular locating plate receives any pin head of the plurality of the pins, while with the two pin cartridges in the closed state, at least one of the plurality of holes receives one pin head of the plurality of the pins extending out of one of the two weight plate holders, thereby preventing the rotation of the handle relative to the two weight plate holders.

4. The weight-adjustable dumbbell according to claim 3 , wherein each of the plurality of weight plates comprises a first groove and two second grooves and, with the two pin cartridges in the closed state, at least one of the plurality of pins has the pin head inserted into one of the plurality of holes of the circular locating plates and the pin bottom inserted into the second grooves of one of the plurality of weight plates, thereby locking the corresponding weight plate to one of the two weight plate holders.

5. The weight-adjustable dumbbell according to claim 4 , wherein the dumbbell has two states: an operating state in which the two pin cartridges are in the closed state, the handle is not rotatable relative to the two weight plate holders and the dumbbell is ready to be used by a user; and a weight adjusting state in which the two pin cartridges are in the open state, the handle is rotatable relative to the two weight plate holders to one of predefined positions and the dumbbell is changeable to a predetermined weight according to a value marked for each of the predefined positions which the handle is rotated to.

6. The weight-adjustable dumbbell according to claim 4 , wherein each of the predefined positions, to which the handle is configured to be rotated, defines an alignment of one of the plurality of fan-shaped sectors of the circular locating plate with one end of one of the two pin cartridges, and such alignment allows a set of the pin heads of the plurality of pins respectively being inserted into a set of the plurality of holes within the sector of the plurality of fan-shaped sectors of the circular locating plate.

7. The weight-adjustable dumbbell according to claim 1 , wherein each of the plurality of weight plates has a first groove and two second grooves which are symmetric so that each plate of the plurality of weight plates fits either of the two weight plate holders, and each plate of the plurality of weight plates is configured to flip sides but still fits either of the two weight plate holders and the base.

8. The weight-adjustable dumbbell according to claim 1 , further comprising a locking structure linked to a locating pin, capable of locking one of the two pin cartridges in the closed state in which the locating pin extending from one of the two pin cartridges is inserted into a corresponding locating hole in the circular locating plate.

9. The weight-adjustable dumbbell according to claim 1 , wherein the base comprise a number of arc-shaped grooves separated by separation ribs, and each of the number of arc-shaped grooves is for holding one of the plurality of weight plates when the dumbbell is in the process of adjusting its weight by rotating the handle relative to the two weight plate holders or when the dumbbell is not in use.