Positioning and push-in arrangement for a track device

A track device comprises a first track and a second track slidably received in the first track. An engaging member is mounted to an end of the first rack and includes at least one positioning block. The second track further includes two hooks for engaging with two ends of a pressing member mounted to the second track. The pressing member includes a protruded portion that can be pressed. The pressing member further includes at least one notch defined by two parallel walls. When the second track is pulled outward along a longitudinal direction, the notch is engaged with the positioning block of the engaging member of the first track, thereby providing a better positioning effect. When the protruded portion of the pressing member is pressed, the notch is disengaged from the positioning block, thereby allowing disengagement or engagement of the second track from or into the first track.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment in accordance with the present invention will now be described with reference to the accompanying drawings. Referring to FIG. 1, a three-part track device in accordance with the present invention generally includes a first track 1 and a second track 2 . The first track 1 includes an upper longitudinal lip 11 and a lower longitudinal lip 11 for guiding sliding movement of the second track 2 in the first track 1 . A slide-aiding member 12 is provided between the first track 1 and the second track 2 . In this preferred embodiment, the slide-aiding member 12 extends to inner surfaces of the upper and lower lips 11 and includes a plurality of balls 13 to provide a rolling contact between the first track 1 and the second track 2 . A stop 14 is formed on an end of the first track 1 to prevent disengagement of the second track 2 from the first track 1 after the second track 2 is mounted into the first track 1 . An engaging member 15 is mounted to the other end of the first track 1 . In this embodiment, the engaging member 15 includes two protrusions 151 for engaging with two openings 16 of the first track 1 . If desired, the engaging member 15 can be bonded by adhesive or rived to the openings 16 of the first track 1 . The engaging member 15 further includes two upright walls 17 each having a cylindrical portion 171 that abuts against an associated longitudinal lip 11 , 21 of the first track 1 and the second track 2 ( FIG. 5 ). Thus, a smoother sliding motion is provided between the first track 1 and the second track 2 . The engaging member 15 further includes two positioning blocks 18 on a side thereof that faces away from the protrusions 151 . Each positioning block 18 is adjacent to a respective upright wall 17 . The engaging member 15 further includes a resilient abutting portion 19 that extends from an end thereof. The second track 2 is mounted into the first track 1 and slidable between the upper longitudinal lip 11 and the lower longitudinal lip 11 . The second track 2 includes an upper longitudinal lip 21 and a lower longitudinal lip 21 that correspond with the upper longitudinal lip 11 and the lower longitudinal lip 11 of the first track 1 , respectively. The slide-aiding member 12 and the cylindrical portion 171 of each upright wall 17 is located between a respective longitudinal lip 11 and its associated longitudinal lip 21 , thereby allowing smoother sliding motion between the first track 1 and the second track 2 . A stop 22 is provided on an end of the second track 2 . The stop 22 abuts against the abutting portion 19 on the engaging member 15 of the first track 1 to thereby stop sliding motion of the second track 2 relative to the first track 1 . The first track 1 and the second track 2 have a relatively smaller overall length in this case, while the other end of the second track 2 abuts against the stop 14 on the first track 1 . A pressing member 23 is mounted to the second track 2 . In this embodiment, the second track 2 includes two longitudinally spaced hooks 24 for engaging with two ends of the pressing member 23 , respectively. The pressing member 23 includes a protruded portion 29 between two lateral sides thereof to provide certain compressibility. Namely, the profile of the protruded portion 29 of the pressing member 23 can be lowered with respect to the plane of the pressing member 23 engaged on the second track 2 . The pressing member 23 further includes a notch 25 in each of two lateral sides thereof, each notch 25 being defined by two parallel walls 26 that extend in a direction perpendicular to a longitudinal direction of the engaging member 23 . At least one of the walls 26 includes an inclined portion 27 on an upper side thereof. The inclined portion 27 may guide the associated positioning block 18 to move across the upper side of the associated wall 26 . When the positioning blocks 18 abut against the inclined portions 27 , the protruded portion of the pressing member 23 is lowered such that the positioning blocks 18 are engaged with the notches 25 , respectively. Thus, the first track 1 and the second track 2 have a reliable positioning effect therebetween when they are at the maximum overall length. In addition, when the second track 2 is telescoped into the first track 1 from the maximum overall length, a relatively large force must be applied to overcome the force imparted to the walls 26 from the positioning blocks 18 . The positioning blocks 18 move across the upper sides of the walls 26 and thus allow the second track 2 to be telescoped into the first track 1 . The positioning blocks 18 are disengaged with the notches 25 when the protruded portion 29 of the pressing member 23 is pressed. Namely, the walls 26 of the notches 25 cannot abut against the positioning blocks 18 , and the pressing member 23 may move across the engaging member 15 , thereby allowing the second track 2 to be separated from the first track 1 . The first track 1 and the second track 2 in FIGS. 2 and 3 are engaged together, and the overall length of the first track 1 and the second track 2 is smaller. In this case, the protruded portion 29 of the pressing member 23 extends beyond the surface of the second track 2 and thus has a higher profile. Referring to FIGS. 4 and 5 , when the second track 2 is moved relative to the first track 1 to a position that the overall length of the first track 1 and the second track 2 is the maximum without causing disengagement of the second track 2 from the first track 1 , the protruded portion 29 of the pressing member 23 is still not depressed and thus has a higher profile. The positioning blocks 18 of the engaging member 15 are engaged with the notches 25 and thus provide a reliable positioning effect for the first track 1 and the second track 2 . When telescopic motion of the second track 2 relative to the first track 1 is required, a larger force is applied. In addition, when the positioning blocks 18 are engaged in the notches 25 of the pressing member 23 , the second track 2 cannot be pulled outward away from the first track 1 , namely, the second track 2 cannot be disengaged from the first track 1 . Referring to FIGS. 6 and 7 , when disengaging the second track 2 from the first track 1 or mounting the second track 2 into the first track 1 , the protruded portion 29 of the pressing member 23 on the second track 2 is pressed to disengage the positioning blocks 18 of the engaging member 15 from the notches 25 , thereby allowing disengagement of the second track 2 from the first track 1 or mounting of the second track 2 into a space between the upper and lower longitudinal lips 11 of the first track 1 . According to the above description, when the second track 2 and the first track 1 are at their maximum overall length, the positioning blocks 18 of the engaging member 15 are engaged with the notches 25 of the pressing member 23 , thereby providing a better positioning between the first track 1 and the second track 2 . In addition, when the second track 2 is required to be telescoped into the first track 1 , a relatively larger instant force is applied to make the positioning blocks 18 move across the upper portions of the walls 26 . Namely, the second track 2 is telescoped into the first track 1 . Furthermore, by means of pressing the protruded portion 29 of the pressing member 23 , the positioning blocks 18 of the engaging member 15 are disengaged from the notches 25 of the pressing member 23 , thereby allowing disengagement or engagement of the second track 2 from or into the first track 1 . The assembly or detachment is easy. Although the invention has been explained in relation to its preferred embodiment as mentioned above, it is to be understood that many other possible modifications and variations can be made without departing from the scope of the invention. It is, therefore, contemplated that the appended claims will cover such modifications and variations that fall within the true scope of the invention.