GB2502822A

GB2502822A - Foldable leg rest

Info

Publication number: GB2502822A
Application number: GB1210145.7A
Authority: GB
Inventors: qing-kun Yin; Chin-Chen Chang
Original assignee: WAN YU LI
Current assignee: WAN YU LI
Priority date: 2012-06-08
Filing date: 2012-06-08
Publication date: 2013-12-11
Anticipated expiration: 2032-06-08
Also published as: GB2502822B; GB201210145D0

Abstract

A foldable leg rest has a slide base 20, a first folding assembly, a second folding assembly, a first stage drive mechanism 50 and a second stage drive mechanism 60. The slide base 20 has a slide frame 21. The first folding assembly has a first frame 30 pivotally connected to the slide frame 21 and two guide pieces having a slot for a rolling bearing on a projection of a support arm 24 of the slide base to move along. The second folding assembly has a second frame 40 pivotally connected to the first frame 30. In use, the first stage drive mechanism 50 is operated to drive the first frame 30 to pivot relative to the slide frame 21 and the second stage drive mechanism 60 is operated to drive the second frame 40 to pivot relative to the first frame 30. Therefore, the legs of a sitter can be stretched and placed on the folding assemblies so as to enhance comfort and minimize fatigue, possibly on a vehicle journey.

Description

FOLDABLE LEG REST

1. Field of the Invention

The present invention relates to a leg rest, and more particularly to a foldable leg rest mounted on a seat of a chair for supporting the legs of a sitter in a stretched position.

2. Description of the Prior Arts

Chairs allow people to sit thereon and support weights of sitters. A conventional chair substantially comprises a seat and a backrest for supporting the back of a sitter. The backrest may be adjustable in angle relative to the seat by an angle adjuster to fit different needs of different sitters.

However, when a person sits on the chair for a long time, for example on a long vehicle trip, the legs of the sitter on the conventional chair will become tired and numb, or pain due to long time of bending. Accordingly, the conventional chair should be fhrther improved to provide an enhanced comfort for the sitter.

The main object of the present invention is to provide a foldable leg rest that supports the legs of a sitter in a stretched position.

To achieve the foregoing objective, the foldable leg rest in accordance with the present invention comprises a slide base, a first folding assembly, a second folding assembly, a first stage drive mechanism and a second stage drive mechanism. The slide base includes a slide frame and two supporting arms. The slide frame has two sides and a front end. The supporting arms are respectively slidably mounted on the sides of the slide frame and each supporting arm has a front end, a projection, a rolling bearing and a roller. The projection extends from the front end of the supporting arm. The rolling bearing and the roller are mounted on the projection. The first folding assembly includes a first frame and two guide pieces. The first frame has a front end, a rear end and a bottom surface. The rear end of the first frame is pivotally connected to the front end of the slide frame. The guide pieces are respectively secured to two side portions of the bottom surface of the first frame and each guide piece has a guide slot for allowing the projection of a corresponding supporting arm to extend therethrough and to move therealong. The second folding assembly includes a second frame having a rear end pivotally connected to the front end of the first frame. The first stage drive mechanism is mounted on the slide base. The second stage drive mechanism is mounted on the first frame. In use, the first stage drive mechanism is operated to drive the first frame to pivot relative to the slide base and the second stage drive mechanism is operated to drive the second frame to pivot relative to the first frame. Therefore, the legs of a sitter can be stretched and placed on the folding assemblies so as to enhance comfort and minimize fatigue.

IN THE DRAWINGS: Fig. I is a top perspective view of a foldable leg rest in accordance with the present invention shown in an unfolded state; Fig. 2 is a bottom perspective view of the foldable leg rest in Fig. 1 shown in an unfolded state; Fig. 3 is a perspective view of a mounting bracket and a slide base of the foldable leg rest in Fig. 1; Fig. 4 is a partially enlarged expthded perspective view of a first stage drive mechanism of the foldable leg rest in Fig. 1; Fig. 5 is an enlarged perspective view of a second stage drive mechanism of the foldaHe leg rest in Fig. 1; Fig. 6 is a partially enlarged exploded perspective view of the second stage drive mechanism of the foldaHe leg rest in Fig. 1; Fig. 7 is an enlarged perspective view of a third stage drive mechanism of the foldable leg rest hi Fig. 1; Fig. 8 is a perspective view of a chair with the foldable leg rest in Fig. 1; and Figs. 9 to 13 are operational side views of the foldable leg rest in Fig. 1.

With reference to Figs. I and 2, a foldable leg rest in accordance with the present invention comprises a mounting bracket 10, a slide base 20, a first folding assembly, a second folding assembly, a first stage drive mechanism 50, a second stage drive mechanism 60, a third stage drive mechanism 70 and a fourth stage drive mechanism 80.

The motmting bracket 10 includes a mounting frame 11 and two tracks 12. The mounting frame 11 has two sides. The tracks 12 are respectively secured to the sides of the mounting frame 11.

With reference to Figs. 1 and 3, the slide base 20 is slidably moimted on the mounting bracket 10 and includes a slide frame 21, two first slide blocks 22, two second slide blocks 23, two supporting arms 24, a driven board 25, a first mounting board 26 and a second mounting board 27. The slide frame 21 has two sides, a front end and two pivot pieces 211. The pivot pieces 211 respectively extend from two sides of the front end of the slide frame 21.The first slide blocks 22 are respectively secured to the sides of the slide frame 21, respectively slidably engage the tracks 12 of the mounting bracket 10 and each first slide block 22 has a middle portion, a rear portion and an outer surface.

The second shde blocks 23 are respectiv&y secured to the outer surfaces of the first slide blocks 22. The supporting arms 24 are respectively slidably mounted on the sides of the slide frame 21 and each supporting arm 24 has a front end, a rear portion, a chute 241, a projection 242, a rolling bearing 243 and a roller 244. The chute 241 is formed in tile rear portion of the supporting arm 24 for allowing a corresponding second slide block 23 to slidably engage therewith.

The front end of the supporting arm 24 protrudes out of the front end of the slide frame 21. The projection 242 extends from the front end of tile supporting arm 24. The rolling bearing 243 and the roller 244 are mounted on the projection 242. The driven board 25 has its opposite ends respectively secured to the rear portions of tile supporting arms 24. The first mounting board 26 has its opposite ends respectively secured to the rear portions of the first slide blocks 22. The second mounting board 27 has its opposite ends respectively secured to tile middie portions of the first slide biocks 22.

With further reference to Fig. 7, the first foMing assembly includes a first frame 30, two pivot pins 31, two guide pieces 33, two limit blocks 34, two insertion rods 35, two first contact switches 36, a second front contact switch 37 and a second rear contact switch 37A. The first frame 30 is pivotally connected to the slide frame 21 and has a bottom sm-face, two sides, a front wafi and two bores 32. The bottom surface of the first frame 30 has two side portions, a middle portion and a rear portion. Each side of the first frame 30 has a front end and a rear end. The front wall of the first frame 30 has two sides.

The bores 32 are respectively formed through the sides of the front wall of the first frame 30. The pivot pins 31 are respectively mounted through the pivot pieces 211 of the slide frame 21 and the rear ends of the sides of the first frame to connect the slide frame 21 and the first frame 30 pivotally. The guide pieces 33 are respectively secured to the side portions of the bottom surface of the first frame 30 and respectively correspond to the supporting arms 24 of the slide base 20. Each guide piece 33 has a guide slot 331 for allowing the projection 242 of the corresponding supporting arm 24 to extend therethrough and to move therealong. The limit blocks 34 are respectively secured to the side portions of the bottom surface of the first frame 30 between tile guide pieces 33.

Each limit block 34 has an inner surface, a front surface and a hole 341. The holes 341 of the two limit blocks 34 respectively align with the bores 32 of the front wall of the first frame 30. The insertion rods 35 are respectiveiy movabiy inserted in the holes 341 of the limit blocks 34. The first contact switches 36 are respectively secured to the front surfaces of the limit blocks 34. The second front and rear contact switches 37, 37A are respectively secured to front and rear portions of the inner surface of one of the limit blocks 34.

With reference to Figs. 1 and 2, the second folding assembly includes a second frame 40. The second frame 40 is pivotaily connected to the first frame and has two sides, a rear wall and two bores 41. Rear ends of the sides of the second frame 40 are respectively pivotally connected to the front ends of the sides of the first frame 30. The rear wail of the second frame 40 has two sides.

The bores 41 are respectively formed through the sides of the rear wall of the second frame 40 and respectively align with tile bores 32 of the first frame 30.

With reference to Figs. I and 3, the first stage drive mechanism 50 is mounted on the slide base 20, is operated to drive the first frame 30 to pivot relative to the slide base 20 and includes a first stage direct current (DC) motor Si, a first stage gearing 52, a first stage threaded rod 53 and a first stage nut 54.

The first stage DC motor 5 1 is secured to the first mounting board 26 of the slide base 20 by a comiecting member 511. With further reference to Fig. 4, the first stage gearing 52 has a housing secured to the second mounting board 27 of the slide base 20 and receiving a first stage pivot shaft 521, a first stage first gear 522 and a first stage second gear 523. The pivot shaft 52i is driven by the DC motor 51 and has a gear 52 formed on one end thereof The first stage first gear 522 meshes with the gear 5211 of the pivot shaft 521.The first stage second gear 523 is coaxiaily mounted on the first stage first gear 522. The first stage threaded rod 53 has a gear 531 foniied on one end thereof and meshing with the first stage second gear 523. The first stage nut 54 is screwed onto the first stage threaded rod 53 and is secured to the driven board 25 of the slide base 20 so that the first stage nut 54 is longitudinally movable along the threaded rod 53.

With reference to Figs. 1 and 5, the second stage drive mechanism 60 is mounted on the first frame 30, is operated to drive the second frame 40 to pivot relative to the first frame 30 and includes a second stage DC motor 61, two second stage driving rods 62 and two second stage gearings 63. The second stage DC motor 61 is secured to the rear portion of the bottom surface of the first frame 30 and has two ends and two flexible shafts 611. The flexible shafts 611 are respectively connected to the ends of the second stage DC motor 61.

The second stage driving rods 62 are respectively driven by a corresponding flexible shaft 611 of the second stage DC motor 61 and each second stage driving rod 62 has a worm 621 formed on one end thereof The second stage gearings 63 are respectively mounted between the front ends of the sides of the first frame 30 and the rear ends of the sides of the second frame 40.

With further reference to Fig. 6, each second stage gearing 63 has a housing secured to the bottom surface of the first frame 30 and receiving a worm gear 631, a second stage first gear 632 and a second stage second gear 633. The worm gear 631 meshes with the worm 621 of a corresponding second stage driving rod 62. The second stage first gear 632 is coaxially mounted on the worm gear 63 1. The second stage second gear 633 meshes with the second stage first gear 632. Each second stage gearing 63 frirther has a second stage third gear 634, a second stage pivot shaft 635, a connecting element 636 and a contacting element 637. The second stage third gear 634 meshes with the second stage second gear 633. The second stage pivot shaft 635 is coaxially and securely mounted through the second stage third gear 634 and has an inner end and an outer end respectively extending from opposite side surfaces of the second stage third gear 634. The connecting element 636 is secured to the outer end of the second stage pivot shaft 635 and has a connecting piece 6361 extending therefrom and secured to the rear end of a corresponding side of the second frame 40. The contacting element 637 is secured to the inner end of the second stage pivot shaft 635 and has a contacting projection 6371 extending

S

therefrom and being contactable with a corresponding first contact switch 36.

With reference to Figs. 1, 2 and 7, the third stage drive mechanism 70 is mounted on the first frame 30, is operated to drive the insertion rods 35 to move in the holes 341 of the limit blocks 34 and includes a third stage DC motor 71, a third stage threaded rod 72, a third stage nut 73 and a wing 74. The third stage DC motor 71 is secured to the middle portion of the bottom surface of the first frame 30. The third stage threaded rod 72 is driven by the third stage DC niotor 71 and has a front end rotatably mounted on the front wall of the first frame 30. The third stage nut 73 is screwed onto the third stage threaded rod 72 and is longitudinally movable thereon. The wing 74 has a bottom surface, a central portion, opposite ends and a contacting rod 741. The central portion of the wing 74 is secured to the third stage nut 73. The ends of the wing 74 are respectively secured to middle portions of the insertion rods 35. The contacting rod 741 extends from one side of the bottom surface of the wing 74, is contactable with the second front or rear contact switch 37, 37A.

With reference to Figs. 2 and 3, the fourth stage drive mechanism 80 is mounted on the slide base 20, is operated to drive the slide base 20 to move relative to the mounting bracket 10 and includes a fourth stage DC motor 81, two fourth stage threaded rods 82 and two fourth stage nuts 83. The fourth stage DC motor 81 is secured to the first mounting board 26 of the slide base 20. The fourth stage threaded rods 82 are respectively disposed at sides of the fourth stage DC motor 81 and are driven by the fourth stage DC motor 81. The fourth stage nuts 83 are respectively screwed onto the fourth stage threaded rods 82 and are respectively secured to inner surfaces of the tracks 12 of the mounting bracket 10 so that the fourth stage threaded rods 82 are longitudinally movable relative to the fourth stage nuts 83.

With reference to Fig. 8, the foldaHe leg rest in accordance with the present invention is applied to a chair that comprises a seat (not shown) and a backrest 90. The mounting bracket 10 is connected to the seat, and rear ends of the first slide blocks 22 of the slide base 20 are connected to the backrest 90.

With reference to Fig. 9, the leg rest is in a folded state. To unfold the leg rest, with reference to Figs. 3, 4 and 10, the first stage DC motor 51 is switched on and drives the pivot shaft 521 to rotate, tile first stage nut 54 is then moved forward along the first stage threaded rod 53 with the transmission of the first stage first gear 522, the first stage second gear 523 and the first stage threaded rod 53, and the driven board 25 to which the first stage nut 54 is secured is then driven to make the chutes 241 of the supporting arms 24 slide relative to the second slide blocks 23 and to make the projections 242 of the supporting arms 24 move along the guide slots 331 of the guide pieces 33. Thus, the first frame can be pivoted forward relative to the slide base 20.

With reference to Figs. 5,6 and 11, the second stage DC motor 61 is switched on and drives the second stage driving rods 62 to rotate, and the second frame 40 can be pivoted forward relative to the first frame 30 with the transmission of the worm gears 631, the second stage first gears 632, the second stage second gears 633, the second stage third gears 634, the second stage pivot shafts 635 and the connecting elements 636. With reference to Figs. and 12, when the second frame 40 is pivoted forward 180 degrees relative to the first frame 30, the contacting projections 6371 of the contacting elements 637 will contact the first contact switches 36. An electric circuit connected to the first contact switches 36 can be detected to determine if the electric circuit is a ioop circuit and to determine if the second stage DC motor 61 should be switched off, thus ensuring that the second frame 40 completes 180 degrees of pivotmg.

With reference to Figs. 7 and 12, the third stage DC motor 71 is switched on and drives the third stage threaded rod 72 to rotate, the third stage nut 73 is then moved forward along the third stage threaded rod 72 with the threaded engagement between the third stage threaded rod 72 and the third stage nut 73, and the wing 74 to which the third stage nut 73 is secured is then driven to make the insertion rods 35 move forward in the holes 341 of the limit blocks 34 and pass through the bores 32 of the first frame 30 and the bores 41 of the second frame 40. Accordingly, front ends and rear ends of the insertion rods 35 are respectively disposed in the first frame 30 and the second frame 40 so as to reinforce tile first frame 30 and the second frame 40. The insertion rods can move forward until the contacting rod 741 of the wing 74 contacts the second front contact switch 37. An electric circuit connected to the second front contact switch 37 can be detected to determine if the eiectric circuit is a loop circuit and to detennine if the third stage DC motor 71 should be switched off, thus ensuring that the insertion rods 35 complete their movement.

With reference to Figs. 3 and 13, the fourth stage DC motor 81 is switched on and drives the fourth stage threaded rods 82 to rotate, the fourth stage threaded rods 82 are then moved forward relative to the fourth stage nuts 83 with the threaded engagement between the fourth stage threaded rods 82 and the fourth stage nuts 83, and the first mounting board 26 to which the fourth stage DC motor 81 is secured is then driven to make the first slide blocks 22 slide relative to the tracks 12. Thus, the slide base 20 and the first and second frames 30, 40 can be moved forward relative to the mounting bracket 10 for allowing a sitter to adjust the space for sitting.

The leg rest in accordance with the present invention includes the folding assemblies to extend its length. Therefore, the legs of the sitter can be stretched and placed on the folding assemblies so as to enhance comfort and minimize fatigue. In addition, the insertion rods 35 passing through the first frame 30 and the second frame 40 can reinforce the strength of the leg rest and prevent collapse thereof To fold the leg rest in accordance with the present invention, with reference to Fig. 3, the fourth stage DC motor 81 is switched on and drives the slide base 20 and the first and second folding frames 30, 40 to move rearward relative to the mounting bracket 10. With reference to Fig. 7, the third stage DC motor 71 is switched on and drives the wings 74 and the insertion rods 35 to move rearward. When the contacting rod 741 of the wing 74 contacts the second rear contact switch 37A, the insertion rods 35 complete their return movement. With reference to Fig. 1, the second stage DC motor 61 is switched on and drives the second frame 40 to pivot toward the bottom surface of the first frame 30. The first stage DC motor 51 is switched on and drives the first frame 30 to pivot rearward. Therefore, an area of the leg rest is reduced and to arrange or store the leg rest is convenient.

Claims

CLAIMS: 1. A foldable leg rest comprising: a slide base (20) including: a slide frame (21) having two sides and a front end; and two supporting arms (24) respectively slidably mounted on the sides of the slide frame (21) and each supporting ann (24) having: a front end; a projection (242) extending from the front end of the supporting arm (24); and a rolling bearing (243) and a roller (244) mounted on the projection (242); a first folding assembly including: a first frame (30) having: a front end; a rear end pivotally connected to the front end of the slide frame (21); and a bottom surface having two side portions; and two guide pieces (33) respectively secured to the side portions of the bottom surface of the first frame (30) and each guide piece (33) having a guide slot (331) for allowing the projection (242) of a corresponding supporting arm (24) to extend therethrough and to move therealong; a second folding assembly including a second frame (40) having a rear end pivotally connected to the front end of the first frame (30); a first stage drive niechanisni (50) niounted on the slide base (20) and operated to drive the supporting arms (24) to slide relative to the slide frame (21) and to make the projections (242) of the supporting arms (24) move along the guide slots (331) of the guide pieces (33) so that the first frame (30) is pivoted relative to the slide base (20); and a second stage drive mechanism (60) mounted on the first frame (30) and operated to drive the second frame (40) to pivot relative to the first frame (30).
2. The foldable leg rest as claimed in claim 1, wherein the slide base (20) indudes a driven board (25) having its opposite ends respectively secured to rear portions of the supporting arms (24); and a first mounting board (26) having its opposite ends respectively secured to rear portions of the slide frame (21); and the first stage drive mechanism (50) includes a first stage DC motor (51) secured to the first mounting board (26) of the slide base (20); a first stage threaded rod (53) driven by the first stage DC motor (51) through a first stage gearing (52); and a first stage nut (54) screwed onto the first stage threaded rod (53) and secured to the driven board (25) of the slide base (20) so that the first stage nut (54) is longitudinally movable along the threaded rod (53).
3. The foldable leg rest as claimed in claim 1 or 2, wherein the second stage drive mechanism (60) includes a second stage DC motor (61) secured to a rear portion of the first frame (30); and two second stage driving rods (62) and two second stage gearings (63) driven by the second stage DC motor (61).
4. The foldable leg rest as claimed in claim 3, wherein the first stage gearing (52) has a first stage pivot shaft (521) driven by the DC motor (51) and having a gear (5211) formed on one end thereof a first stage first gear (522) meshing with the gear (5211) of the pivot shaft (521); and a first stage second gear (523) coaxially mounted on the first stage first gear (522); and the first stage threaded rod (53) has a gear (531) formed on one end thereof and meshing with the first stage second gear (523).
5. The foldable leg rest as claimed in claim 4, wherein each second stage driving rod (62) has a worm (621) formed on one end thereof the second stage gearings (63) are respectively mounted between two sides of the first frame (30) and two sides of second frame (40), and each second stage gearing (63) has a housing secured to the first frame (30) and receiving: a worm gear (631) meshing with the worm (621) of a corresponding second stage driving rod (62); a second stage first gear (632) coaxially mounted on the worm gear (631); and a second stage second gear (633) meshing with the second stage first gear (632); and each second stage gearing (63) further has a second stage third gear (634) meshing with the second stage second gear (633); a second stage pivot shaft (635) coaxially and securely mounted through the second stage third gear (634); and a comiecting element (636) secured to the second stage pivot shaft (635) and having a connecting piece (6361) extending therefrom and secured to a corresponding side of the second frame (40).
6. The foldable leg rest as claimed in claim 5, wherein the first folding assembly includes two first contact switches (36) respectively secured to the sides of the first frame (30); and each second stage gearing (63) has a contacting element (637) secured to the second stage pivot shaft (635) and having a contacting projection (6371) extending therefrom and being contactable with a corresponding first contact switch (36).
7. The foldaHe leg rest as claimed in any claim of claims I to 6, wherein the first frame (30) has a front wall having two sides; and two bores (32) respectively formed through the sides of the front wall of the first frame (30); the first folding assembly includes two limit blocks (34) respectively secured to the side portions of the bottom surface of the first frame (30) and each limit block (34) having a hole (341), tile holes (341) of the two limit blocks (34) respectively aligning with the bores (32) of the front wall of the first frame (30); and two insertion rods (35) respectiv&y movably inserted in the holes (341) of the limit blocks (34); the second frame (40) has a rear wall having two sides; and two bores (41) respectiv&y formed through the sides of the rear wall of the second frame (40) and respectively aligning with the bores (32) of the first frame (30); and wherein the foidaHe ieg rest further comprises a third stage drive mechanism (70) mounted on the first frame (30) and operated to drive the insertion rods (35) to move in the holes (341) of the limit blocks (34) and to pass through the bores (32) of the first frame (30) and the bores (41) of the second frame (40) so that front ends and rear ends of the insertion rods (35) are respectively disposed in the first frame (30) and the second frame (40).
8. The foldaHe leg rest as claimed in claim 7, wherein the third stage drive mechanism (70) includes a third stage DC motor (71) secured to a middle portion of the first frame (30); a third stage threaded rod (72) driven by the third stage DC motor (71) and having a front end rotatably mounted on the front wall of the first franie (30); a third stage nut (73) screwed onto the third stage threaded rod (72) and being longitudinally movable thereon; and a wing (74) having: a central portion secured to the third stage nut (73); mid opposite ends respectiv&y secured to the insertion rods (35).
9. The foldable leg rest as claimed in claim 8, wherein the first folding assembly includes a second front contact switch (37) and a second rear contact switch (37A) respectively secured to front and rear portions of one of the limit blocks (34); and the wing (74) of the third stage drive mechanism (70) has a bottom surface; and a contacting rod (741) extending from one side of the bottom surface of the wing (74) and being contactable with the second front or rear contact switch (37, 37A).
10. The f&dable leg rest as claimed in claim 9 further comprising a mounting bracket (10) and a fourth stage drive mechanism (80), wherein the mounting bracket (10) includes a mounting frame (II) having two sides; and two tracks (12) respectively secured to two sides of the mounting frame (11); the slide base (20) indudes two first slide blocks (22) respectively secured to the sides of the slide frame (21) and respectively slidably engaging the tracks (12) of the mounthig bracket (10); and the fourth stage drive mechanism (80) is mounted on the slide base 20 and operated to drive the slide base (20) to move relative to the mounting bracket (10).
II. The foldable leg rest as claimed in claim 10, wherein the fourth stage drive mechanism (80) includes a fourth stage DC motor (81) secured to the slide frame (21) of the slide base (20); two fourth stage threaded rods (82) driven by the fourth stage DC motor (81); and two fourth stage nuts (83) respectively screwed onto the fourth stage threaded rods (82) and respectively secured to the tracks (12) of the mounting bracket (10) so that the fourth stage threaded rods (82) are longitudinally movable relative to the fourth stage nuts (83).Amendments to the claims have been filed as follows: CLAIMS: 1. A foldable leg rest comprising: a slide base (20) induding: a slide frame (21) having two sides and a front end; and two supporting arms (24) respectively slidably mounted on the sides of the slide frame (21) and each supporting arm (24) having: a front end; a proj ection (242) extending from the front end of the supporting arm (24); and a rolling bearing (243) and a roller (244) mounted on the C") projection (242); a first folding assembly including: 0 a first frame (30) having: (0 r a front end; a rear end pivotafly connected to the front end of the slide frame (21); and a bottom surface having two side portions; and two guide pieces (33) respectively secured to the side portions of the bottom surface of the first frame (30) and each guide piece (33) having a guide slot (331) for allowing the projection (242) of a corresponding supporting arm (24) to extend therethrough and to move therealong; a second folding assembly including a second frame (40) having a rear end pivotally connected to the front end of the first frame (30); a first stage drive mechanism (50) mounted on the slide base (20) and operated to drive the supporting arms (24) to slide relative to the slide frame (21) and to make the projections (242) of the supporting arms (24) move along the guide slots (331) of the guide pieces (33) so that the first frame (30) is pivoted relative to the slide base (20); and a second stage drive mechanism (60) mounted on the first frame (30) and operated to drive the second frame (40) to pivot relative to the first frame (30).2. The foldable leg rest as claimed in claim 1, wherein the slide base (20) includes a driven board (25) having its opposite ends respectively secured to rear C") portions of the supporting arms (24); and a first mounting board (26) having its opposite ends respectively secured 0 to rear portions of the slide frame (21); and (0 r the first stage drive mechanism (50) includes a first stage DC motor (51) secured to the first mounting board (26) of the slide base (20); a first stage threaded rod (53) driven by the first stage DC motor (51) through a first stage gearing (52); and a first stage nut (54) screwed onto the first stage threaded rod (53) and secured to the driven board (25) of the slide base (20) so that the first stage nut (54) is longitudinally movable &ong the threaded rod (53).3. The foldable leg rest as claimed in claim 2, wherein the second stage drive mechanism (60) includes a second stage DC motor (61) secured to a rear portion of the first frame (30); and two second stage driving rods (62) and two second stage gearings (63) driven by the second stage DC motor (61).4. The foldable leg rest as claimed in claim 3, wherein the first stage gearing (52) has a first stage pivot shaft (521) driven by the DC motor (51) and having a gear (521 1) formed on one end thereof; a first stage first gear (522) meshing with the gear (5211) of the pivot C') shaft (521); and a first stage second gear (523) coaxially mounted on the first stage first 0 gear (522); and (0 r the first stage threaded rod (53) has a gear (531) formed on one end thereof and meshing with the first stage second gear (523).5. The foldable leg rest as claimed in claim 4, wherein each second stage driving rod (62) has a worm (621) formed on one end thereof the second stage gearings (63) are each respectively mounted between one side of the first frame (30) and one side of the second frame (40), and each second stage gearing (63) has a housing secured to the first frame (30) and receiving: a worm gear (631) meshing with the worm (621) of a corresponding second stage driving rod (62); a second stage first gear (632) coaxially mounted on the worm gear (631); and a second stage second gear (633) meshing with the second stage first gear (632); and each second stage gearing (63) further has a second stage third gear (634) meshing with the second stage second gear (633); a second stage pivot shaft (635) coaxially and securely mounted through the second stage third gear (634); and a connecting element (636) secured to the second stage pivot shaft (635) C) and having a connecting piece (6361) extending therefrom and secured to a corresponding side of the second frame (40). (06. The foldable leg rest as claimed in claim 5, wherein the first f&ding assembly includes two first contact switches (36) respectively secured to the sides of the first frame (30); and each second stage gearing (63) has a contacting element (637) secured to the second stage pivot shaft (635) and having a contacting projection (6371) extending therefrom and being contactable with a corresponding first contact switch (36).7. The foldable leg rest as claimed in any claim of claims I to 6, wherein the first frame (30) has a front wall having two sides; and two bores (32) respectively formed through the sides of the front wall of the first frame (30); the first folding assembly includes two limit blocks (34) respectiv&y secured to the side portions of the bottom surface of the first frame (30) and each limit block (34) having a hole (341), the holes (341) of the two limit blocks (34) respectively aligning with the bores (32) of the front wall of the first frame (30); and two insertion rods (35) respectively movably inserted in the holes (341) of the limit blocks (34); the second frame (40) has a rear wall having two sides; and C') two bores (41) respectively formed through the sides of the rear wall of the second frame (40) and respectively aligning with the bores (32) of the first frame 0 (30); and (0 r wherein the foldable leg rest further comprises a third stage drive mechanism (70) mounted on the first frame (30) and operated to drive the insertion rods (35) to move in the holes (341) of the limit blocks (34) and to pass through the bores (32) of the first frame (30) and the bores (41) of the second frame (40) so that front ends and rear ends of the insertion rods (35) are respectiv&y disposed in the first frame (30) and the second frame (40).8. The foldable leg rest as claimed in claim 7, wherein the third stage drive mechanism (70) includes a third stage DC motor (71) secured to a middle portion of the first frame (30); a third stage threaded rod (72) driven by the third stage DC motor (71) and having a front end rotatably mounted on the front wall of the first frame (30); a third stage nut (73) screwed onto the third stage threaded rod (72) and being longitudin&ly movable thereon; and a wing (74) having: a central portion secured to the third stage nut (73); and opposite ends respectively secured to the insertion rods (35).9. The foldable leg rest as claimed in claim 8, wherein the first f&ding assembly indudes a second front contact switch (37) and a second rear contact switch (37A) respectively secured to front and rear portions of one C') of the limit blocks (34); and the wing (74) of the third stage drive mechanism (70) has 0 a bottom surface; and (0 r a contacting rod (741) extending from one side of the bottom surface of the wing (74) and being contactable with the second front or rear contact switch (37, 3 7A).10. The foldable leg rest as claimed in claim 9 further comprising a mounting bracket (10) and a fourth stage drive mechanism (80), wherein the mounting bracket (10) includes a mounting frame (11) having two sides; and two tracks (12) respectively secured to the two sides of the mounting frame (11); the slide base (20) includes two first shde blocks (22) respectively secured to the sides of the slide frame (21) and respectively slidably engaging the tracks (12) of the mounting bracket (10); and the fourth stage drive mechanism (80) is mowited on the slide base (20) and operated to drive the shde base (20) to move relative to the mounting bracket (10).11. The foldable leg rest as claimed in claim 10, wherein the fourth stage drive mechanism (80) includes a fourth stage DC motor (81) secured to the slide frame (21) of the slide base (20); two fourth stage threaded rods (82) driven by the fourth stage DC motor (81); C') and two fourth stage nuts (83) respectiv&y screwed onto the fourth stage threaded 0 rods (82) and respectively secured to the tracks (12) of the mounting bracket (10) so (0 r that the fourth stage threaded rods (82) are longitudinally movable relative to the fourth stage nuts (83).