the invention will be described in more detail by the following examples in reference to the accompanied drawings . fig1 shows a locking device according to one example of the invention . the locking device comprises a locking element 30 and guiding devices 31 , 32 , which are cooperated to lock an adjustment element 10 . in the example , the locking element 30 comprises a upper locking portion 35 and a lower locking portion 36 , with each of the locking portions comprises a first through hole 351 , 361 and a second through hole 352 , 362 in communication with the first through hole . the first through hole 351 , 352 has a dimension greater than or equal to that of an end surface 102 of the adjustment element 10 . the second through hole 352 , 362 has a dimension less than that of the end surface 102 . therefore , the adjustment element 10 , which is disposed on a carrier element 20 , can pass through the first through hole 351 , 352 , but not the second through hole 352 , 362 . the locking element 30 further comprises an upper securing portion 354 at the upper locking portion 35 , a lower securing portion 364 at the lower locking portion 36 , an actuating arm 40 ( fig1 ) passing through the upper securing portion 354 , and a fixing element 329 ( fig5 ) passing through the lower securing portion 364 . in the example , the upper and lower locking portions 35 , 36 are detachably connected by a linkage element 33 . the detachable connection can be achieved by a number of methods known in the art . in the present example , linkage holes 356 , 366 are respectively provided to the upper and lower locking portions 35 , 36 , and are connected to hooks 331 provided at both ends of the linkage element 33 , such that the upper and lower locking portions 35 , 36 are connected . in other examples , the upper and lower locking portions 35 , 36 are form in a single piece , as shown in fig7 . in this situation , no linkage element 33 is necessary . with reference again to fig1 , the guiding device comprises an upper guiding element 31 and a lower guiding element 32 . as shown in more detail in fig2 and 3 , the upper guiding element 31 comprises a first guiding slot 314 along which the locking element 30 is able to slide ; a supportive platform 313 for supporting the actuating arm 40 ; a first cavity 312 for receiving one of the adjustment elements 10 ; and a carrying platform 319 for carrying the upper securing portion 354 of the locking element 30 . in the example , the first guiding slot 314 is interrupted between the supportive platform 313 and the carrying platform 319 . in another example , the first guiding slot 314 is continuous as long as the guiding elements provide a passage for the actuating arm to pass through and to abut against the supportive platform 313 . in the example , see fig4 and 5 , the lower guiding element 32 comprises a second guiding slot 324 . the locking element 30 is able to slide along the first guiding slot 314 and enters into the second guiding slot 324 and slides therein . the lower guiding element 32 further comprises a second cavity 322 for receiving other of the adjustment element 10 , an elastic element 321 for providing elastic force when in contact with the lower securing portion 364 , and a third cavity 323 located below the second cavity 322 and having the elastic element 321 received therein . the fixing element 329 passes through the lower securing portion 364 and also the elastic element 321 and is fixed to an upper wall 325 of the third cavity 322 . in the example , the elastic element 321 is a spring . the upper and lower guiding elements 31 , 32 are connected to the stationary frame by suitable methods . in the example , see fig2 to 5 , the upper and lower guiding elements 31 , 32 each has linkage elements 316 , 318 and 326 , 328 respectively . a plurality of threaded holes are provided at bottom side of the stationary frame 60 , wherein a threaded hole 62 is position in corresponding to the linkage elements such as 316 , 318 , such that the guiding elements 31 , 32 are connected to a space 63 of the stationary frame 60 by fasteners . in another example , with reference to fig1 - 19 , the upper guiding element 31 has an extension 310 where at least one locking recess 311 is provided . between the extension 310 and the carrying platform 319 and also on the supportive platform 313 are formed with locking slots 315 , with the locking recess 311 adjacent the path of the locking slots 315 . similarly , the lower guiding element 32 has an extension 320 where at least one locking recess 327 is provided . on the lower guiding element 32 is formed with a locking slot 380 , with the locking recess 327 adjacent the path of the locking slot 380 . the stationary frame 60 has a guiding groove 66 defined by two ridges 65 which are able to insert into the locking slots 315 , 380 , such that the upper and lower guiding elements 31 , 32 can slide along the stationary frame 60 . when the guiding elements 31 , 32 is suitably positioned , the ridges 65 will be pressed by a tool ( such as a screw driver ) in alignment with the recesses 311 , 327 , so that the ridges will be deformed and forced into the recesses . the guiding elements 31 , 32 will then be prevented from sliding and connected to the stationary frame 60 . the stationary frame 60 can be attached to a suitable surface , such as a wall surface , by suitable methods . in the example , threaded holes 61 are provided at the bottom side of the frame 60 such that the frame can be attached to the wall surface by fasteners . the person skilled in the art will know other ways to achieve the attachment . with reference again to fig1 and 7 , in the example , the locking element 30 further comprises one or more intermediate locking portions 34 , each comprises a first through hole 341 and a second through hole 342 in communication therewith . the first through hole 341 has a dimension greater than or equal to that of the end surface 102 of the adjustment element 10 . the second through hole 342 has a dimension less than that of the end surface 102 . correspondingly , the guiding device further comprises one or more intermediate guiding elements 37 , each preferably having same structures as the upper guiding element 31 . for purpose of standardization , each of the upper locking portion 35 , lower locking portion 36 and possibly existed intermediate locking portions 34 further comprises a third through hole 353 , 343 or 363 which is in communication with the first through hole 351 , 341 , 361 and symmetrically positioned with respect to the second through hole 352 , 342 , 362 about the first through hole 351 , 341 , 361 . the third through hole 353 , 343 , 363 has a dimension less than that of the end surface 102 and preferably same as that of the second through hole 352 , 342 , 362 . in the example , the upper guiding element 31 has a spacer 317 arranged between the supportive platform 313 and the carrying platform 319 , such that the upper guiding element 31 has a height matching with that of the locking element 30 . with reference to fig8 , it is shown an exemplary adjustment device which comprises the adjustment element 10 and a carrier element 20 carrying the element 10 . the adjustment element 10 has a smooth side surface 104 , exposed when loaded on the carrier element 20 . the adjustment element 10 has end surfaces 102 , a top surface 106 and a bottom surface ( not shown ). in the example , at least one of the top surface and the bottom surface is provided with a sliding groove 11 . in other examples , the sliding groove can also be absent . the carrier element 20 comprises connection wings 12 for connecting to a movable frame 50 ( fig1 ), an upper loading frame 14 connecting to the connection wings 12 , a lower loading frame 13 in parallel with the upper loading frame 14 and in connection with the connection wings 12 , and an opening 17 which , together with the upper and lower loading frames 14 , 13 , defines a space 16 for receiving the adjustment element 10 . in the example , a portion of at least one of the upper and lower frames 14 , 13 forms a guiding rail for engaging within the sliding groove 11 such that the adjustment element 10 can be stably received within the space 16 . in other examples , when the adjustment element 10 is not provided with the sliding groove 11 , the adjustment element 10 has a height slightly greater than that of the opening 17 , such that the adjustment element 10 can be received in the space 16 by virtue of its flexibility . in the example , the adjustment element 10 has a length equal to that of the space 16 . in other examples , the adjustment element 10 has a length slightly smaller / greater than that of the space 16 . in the example , the carrier element 20 further comprises a front blocking plate 15 connecting with the free ends of the upper and lower loading frames 14 , 13 , respectively , in order to prevent the adjustment element 10 from moving outside the space 16 . when the adjustment element 10 is received in the space 16 , one of the end surfaces 102 is in contact with the front blocking plate 15 . in other examples , the front blocking plate 15 may be absent . with reference to fig9 , it is shown the adjustment element 10 and the carrier element 20 when assembled . as shown , when the adjustment element 10 is loaded on the carrier element 20 , the two side surfaces 104 of the adjustment element 10 are exposed outside . the top surface 106 is in contact with the top loading frame 14 , and one of the end surfaces 102 abuts against the front blocking plate 15 , and the other end surface 102 is accommodated in the opening 17 . fig1 shows the assembly of the adjustment device with an exemplary movable frame 50 . the movable frame 50 is provided with a receiving groove 51 into which the wings 12 can be inserted so that the whole adjustment device can be attached to the movable frame 50 and slide along the groove 51 . fig1 shows the assembly of one adjustment device , the upper locking portion 35 and the upper guiding element 31 . as shown , the adjustment device passes through the first through hole 351 and into the first cavity 312 of the upper guiding element 31 . the upper locking portion 35 is inserted into the first guiding slot 314 . the actuating arm 40 ( a threaded rod in this example ) passes through the upper securing portion 354 and the through hole 316 of the carrying platform 319 and then abuts against the supportive platform 313 . in the state as shown , the adjustment device can pass through the first through hole 351 and the first cavity 312 freely , so the position and angle of the movable frame 50 can be adjusted freely in relative to the stationary frame 60 . fig1 shows that the adjustment device is forced into the second through hole 352 such that it is locked . specifically , when the position of the movable frame 50 in relation to the stationary frame 60 is determined , by rotation of the actuating arm 40 , the upper locking portion 35 will move upward due to counterforce , because the actuating arm 40 has one terminal end abutting against the supportive platform 313 and thus cannot move downward . however , the first cavity 312 is not able to move upward , the adjustment device therefore will be forced into the second through hole 352 . in the present invention , the adjustment element 10 is generally made from flexible materials , such as rubbers , pu or modified pu , while the locking device is generally made of rigid materials , for example engineered plastics such as polyformaldehyde or nylon 66 , or zinc alloy . therefore , the adjustment element 10 can be forced into the second through hole 352 by application of forces . when forced into the second through hole 352 , the adjustment device will be unable to move in relative to the stationary frame 60 . therefore , relative position between the movable frame 50 and the stationary frame 60 is fixed . fig1 and 14 show the assembly of an adjustment device with an intermediate locking portion 34 and an intermediate guiding element 37 . the locking of the adjustment device by the locking portion 34 is similar to that as shown in fig1 and 12 , except that the intermediate locking portion 34 does not need additional actuating arm 40 , but instead , is moved upward by virtue of the linkage element 33 or along with the upper locking portion 35 when formed into one piece therewith . fig1 and 16 show the assembly of an adjustment device with the lower locking portion 36 and the lower guiding element 32 . in fig1 , the adjustment device can pass the first through hole 361 and the second cavity 322 freely , so that the position and angle of the movable frame 50 can be freely adjusted in relation to the stationary frame 60 . as shown , the elastic element 321 is in its relaxed or slightly compressed state . by similar principle as that shown in fig1 and 12 , the adjustment device is locked by the lower locking portion 36 , except that the lower locking portion 36 does not need additional actuating arm 40 , but instead , is moved upward by virtue of the linkage element 33 or along with the upper locking portion 35 when formed into one piece therewith . in the locked state , the elastic element 321 is in its compressed state due to the upward movement of the lower locking portion 36 . when the relative position between the movable frame 50 and the stationary frame 60 needs to be changed , by contrarotation of the actuating arm 40 , the whole locking device is pushed to move downward along the first and second guiding slots 314 , 324 due to the elastic force of the elastic element 321 , such that the adjustment device is released from the second through hole 352 , 342 , 362 and returns back to the first through hole 351 , 341 , 361 where the adjustment device can freely move again . it should be understood that various example embodiments have been described with reference to the accompanying drawings in which only some example embodiments are shown . the present invention , however , may be embodied in many alternate forms and should not be construed as limited to only the example embodiments set forth herein .