TWI488570B - Portable electronic device and its hinge assembly - Google Patents

Description

Portable electronic device and hinge assembly thereof

The present invention relates generally to a hinge assembly and a portable electronic device including the same, so that the portable electronic device has two or more different states of use.

With the popularity of portable electronic devices (such as notebook computers, tablet computers, etc.), the single-use mode is not enough to attract consumers' attention, so portable electronic devices that can have more than two modes of use have been gradually developed. For example, a mobile phone combined with a tablet, a laptop, a tablet, and the like.

Taking a notebook computer and a tablet computer as an example, the notebook computer is mainly composed of a main body having a keyboard and a cover body provided with a display panel, and the tablet computer is mainly composed of a cover body provided with a touch display panel. Therefore, the combination of the two is presented with a body provided with a keyboard and a cover body provided with a touch display panel. In the switching mode of the usage mode, the prior art designs the touch display panel to be selectively plugged and unplugged on the input keyboard, thereby switching the usage mode of the notebook or the tablet. However, in the tablet usage mode, The metal electrical contacts and the snap-in mechanism are directly exposed to the environment, and are susceptible to foreign matter intrusion or moisture erosion, which makes the input keyboard insensitive or unusable. In the notebook mode, when the user wants to use the touch display When the panel is operated, the touch display panel and the input keyboard may be connected only by the snap structure, so that the overall structure of the portable electronic device in the notebook mode is unstable, and the touch display panel is easily pushed down. .

In view of this, the design of the hinge assembly can help to stabilize the overall structure of the portable electronic device in the notebook mode without losing the mode of use of the switchable notebook or tablet. And does not expose the metal electrical contacts and the clamping mechanism directly to the environment.

In view of this, the present invention provides a portable electronic device and a hinge assembly thereof, so that the portable electronic device can be switched to two different usage modes of a notebook computer and a tablet computer, and can still be used in each mode. The components or internal components used are protected from exposure, and the overall structural strength of the portable electronic device in the notebook mode is increased to reduce the probability of component damage.

In order to achieve the above object, the technical means adopted by the present invention is to design a hinge assembly comprising: a first unit; a second unit; a third unit pivotally connected to the second unit and disposed adjacent to the first unit The third unit pivots to the second unit; a translation unit provides a translation direction, the translation unit connects the first unit and the third unit; and an offset unit provides an offset direction, and the The translation direction is not parallel to the offset direction, and the offset unit connects the first unit and the third unit And the first unit slides relative to the third unit by the translation unit and the offset unit along the translation direction in the translation direction.

The present invention further provides a portable electronic device comprising: a main body; a connecting cover body comprising a first end portion and a second end portion, the second end portion connecting the main body, the connecting cover body being rotatable relative to the main body a front cover body movable relative to the connection cover body; a hinge assembly coupled to the first end portion of the connection cover body and the front cover body to slide and rotate the front cover body relative to the connection cover body, first The unit is disposed on the front cover body, and the second unit is disposed on the connection cover body; the first unit slides relative to the third unit in the translation direction and the offset direction by the translation unit and the offset unit, so that the front cover body is opposite to the connection cover body slide.

Therefore, the main advantage of the present invention is that, through the arrangement of the hinge assembly, the front cover body can be pivoted relative to the connection cover body to switch between the two different usage modes of the notebook computer and the tablet computer, and through the connection cover body setting. To protect the hinge assembly in the notebook mode, while supporting the front cover in the tablet mode, and through the front cover, the connection cover and the hinge assembly.

10‧‧‧ Subject

101‧‧‧The fifth side

11‧‧‧ Input components

20‧‧‧Connecting cover

201‧‧‧ first end

202‧‧‧second end

21‧‧‧ pivot ribs

22‧‧‧Connecting cover

221‧‧‧ first side

222‧‧‧ second side

30‧‧‧ front cover

31‧‧‧ front cover

310‧‧‧ display panel

311‧‧‧ third side

312‧‧‧ fourth side

313‧‧‧ Third End

314‧‧‧ fourth end

32‧‧‧ rear cover

321‧‧‧5th end

40‧‧‧Open and close hub components

50‧‧‧Hinge assembly

51‧‧‧ first unit

511‧‧‧First docking wing

512‧‧‧second fixed wing

513‧‧‧First slide rail

514‧‧‧Fixed holes

52‧‧‧Second unit

521‧‧‧Second docking wing

522‧‧‧Second fixed wing

523‧‧‧Axis hole

524‧‧‧stop bumps

53‧‧‧ pivot

530‧‧‧ Limit bumps

531‧‧‧Fixed gasket

54‧‧‧Unit 3

541‧‧‧Second rail

542‧‧‧Axis hole

543‧‧‧Fixed holes

544‧‧‧hook

55‧‧‧Second latch

56‧‧‧First bolt

57‧‧‧ Spring

571‧‧‧First positioning unit

58‧‧‧Offset direction

59‧‧‧Translation direction

1 is a perspective view showing the closed state of the portable electronic device of the present invention.

2 is an enlarged, exploded view of a portion of a portable electronic device of the present invention.

3 is a perspective view showing the state of use of the notebook computer of the portable electronic device of the present invention.

Figure 4 is an exploded view of the hinge assembly of the present invention.

FIG. 5 is a side view of the closed state of the portable electronic device of the present invention.

FIG. 6 is a side view of the use state of the notebook computer of the portable electronic device of the present invention.

Fig. 7 is a perspective view showing the hinge assembly of the present invention in a state in which the notebook computer is in use.

Fig. 8 is a perspective view showing another perspective of the hinge assembly of the present invention in a state in which the notebook computer is in use.

Figure 9 is a side elevational view of the cover body before it is subjected to a pulling force.

Figure 10 is a perspective view of the cover body subjected to a pulling force before the present invention.

Figure 11 is a perspective view of the hinge assembly of the present invention in the case where the front cover is subjected to a pulling force.

Figure 12 is another perspective view of the hinge assembly of the present invention in the case where the front cover is subjected to a pulling force.

13 is a perspective view of another mode of use of the portable electronic device of the present invention.

Figure 14 is a side elevational view of the portable electronic device of the present invention in another mode of use.

15 is another perspective view of another mode of use of the portable electronic device of the present invention.

Figure 16 is a perspective view of the hinge assembly of the portable electronic device of the present invention in another mode of use.

17 is a hinge of the portable electronic device of the present invention in another usage mode Another perspective view of the chain assembly.

18 is a perspective view of a portable electronic device of the present invention in a tablet usage mode.

19 is a side view of a portable electronic device of the present invention in a tablet usage mode.

Figure 20 is a perspective view of the hinge assembly of the tablet in use mode of the present invention.

Figure 21 is another perspective view of the hinge assembly of the tablet in use mode of the present invention.

The technical means adopted by the present invention for achieving the intended purpose of the invention are further described below in conjunction with the drawings and preferred embodiments of the invention.

As shown in FIG. 1 to FIG. 3 , the portable electronic device of the present invention comprises a main body 10 , a connecting cover 20 , a front cover 30 , an opening and closing hinge assembly 40 , and a hinge assembly 50 .

As shown in FIG. 3, the main body 10 has a fifth surface 101. An input component 11 is disposed on the fifth surface 101. The input component 11 can be a component such as a keyboard component or a touch panel for inputting data. The electronic components that provide the main functions of the portable electronic device, such as a motherboard and a hard disk, are generally known in the art, and therefore will not be further described herein.

Referring to FIG. 1 to FIG. 3 , the connecting cover 20 has a first end portion 201 , a second end portion 202 , a pivoting rib 21 , and a connecting cover 22 . The second end of the connecting cover 20 is connected. The connecting portion 202 is connected to the main body 10, the pivoting rib 21 is disposed at the second end portion 202 of the connecting cover body 20, and the pivoting rib 21 is connected to the opening and closing hinge assembly 40, and the connecting cover plate 22 is connected to the pivoting rib 21 The connecting cover 22 has a first surface 221 and a second surface 222 opposite to the first surface 221 for connecting the pivot rib 21 to one end of the opening and closing hinge assembly 40.

Referring to FIG. 1 to FIG. 3 , FIG. 6 , FIG. 10 and FIG. 13 , the front cover 30 is movable relative to the connecting cover 20 , and the front cover 30 includes a front cover 31 and a rear cover 32 . The cover 31 has a third surface 311 and a fourth surface 312 opposite to the third surface 311. The front cover 31 has a third end 313 and a fourth end 314, and the third front cover 31 The surface 311 is provided with a display panel 310. The fourth surface 312 of the front cover 31 faces the first surface 211 of the connecting cover 22. The connecting cover 22 is adjacent to the third end 313 of the front cover 31. 32 abuts against the fourth side 312 of the front cover 31, the rear cover 32 is disposed at the fourth end 314 of the front cover 31, and the rear cover 32 and the connecting cover 22 cover the fourth side of the front cover 31 312, the rear cover 32 has a fifth end portion 321 adjacent to the first end portion 201 of the connection cover body 20.

Referring to FIG. 3, the opening and closing pivot assembly 40 is disposed between the main body 10 and the connecting cover 20 to pivotally connect the main body 10 and the connecting cover 20 to each other. The opening and closing pivot assembly 40 is respectively coupled to the main body 10 and the pivoting rib. 21 is connected, and the opening and closing hinge assembly 40 may include pivots, positioning washers, wear pads, elastic washers, fixing nuts and the like to provide functions such as pivoting and stagnant positioning, which are generally in the technical field. Knowledge, so I won't go into details here.

As shown in FIG. 2, FIG. 4 and FIG. 15, the hinge assembly 50 is disposed between the connecting cover 20 and the front cover 30 so that the front cover 30 can slide and rotate relative to the connecting cover 20, and the hinge assembly 50 The first unit 51, the second unit 52, the third unit 54, a translation unit and an offset unit are included. The first unit 51 and the front cover 30 are fixed to each other, and the second unit 52 and the connection cover 20 are mutually connected. Fixed, the third unit 54 and the second unit 52 are mutually The first unit 51 and the third unit 54 are connected to the first unit 51 and the third unit 54 to slide the first unit 51 relative to the third unit 54 in an offset direction 58. The translation unit connects the first unit 51 and the third unit 54 to The first unit 51 slides relative to the third unit 54 in a translational direction 59, the translational direction 59 being different from the offset direction 58 and not parallel.

In a preferred embodiment, the first unit 51 includes a first butt wing 511 and a first fixed wing 512 that are perpendicular to each other. The first fixed wing 512 is fixed to the fourth surface 312 of the front cover 31 of the front cover 30. The second unit 52 includes a second butt wing 521 and a second fixed wing 522 which are perpendicular to each other. The second fixed wing 522 is fixed to the first surface 221 of the connecting cover 22 of the connecting cover 20, and the second unit 52 The second connecting blade 521 includes a stop protrusion 524. The third unit 54 and the second unit 52 are pivotally connected through a penetrating pivot 53. The pivot 53 is respectively disposed in the shaft hole 523 of the second unit 52. In the shaft hole 542 of the third unit 54, the pivot 53 can rotate synchronously with the third unit 54. The end of the pivot 53 can be fixed to the axial position through a fixing washer 531 to avoid separation from the second unit 52. The shaft 53 protrudes in the radial direction to form an arc-shaped limiting protrusion 530. When the third unit 54 rotates relative to the second unit 52, the arc-shaped limiting protrusion 530 and the stopping protrusion 524 are mutually resisted. A maximum angle is formed between the third unit 54 and the second unit 52; the offset unit includes a first sliding rail 513 and a first latch 56. The first sliding rail 513 is formed on the first connecting wing 511 of the first unit 51. The first latch 56 is slidably disposed in the first sliding rail 513 and disposed in the fixing hole 543 of the third unit 54. The second slide rail 541 is formed on the third unit 54 . The second latch 55 is slidably disposed on the second slide rail 541 and disposed on the first unit 51 . It The sliding path provided by the first sliding rail 513 is different from the sliding stroke provided by the second sliding rail 541 and is not parallel. Preferably, the first sliding rail 513 is bent and the second sliding The rail 541 is linear, the first rail 513 forms a curved sliding stroke to provide an offset direction 58 and the second rail 541 forms a linear sliding stroke to provide a translational direction 59; in other embodiments, The first slide rail is disposed on the third unit and the first plug is disposed on the first unit, the first plug is slidably disposed on the first slide rail, and the second slide rail is disposed on the first unit and the second plug is disposed In the third unit, the second latch is slidably disposed on the second slide rail, and details are not described herein.

Referring to FIG. 4 , FIG. 10 and FIG. 13 , the plurality of first positioning units 571 are respectively disposed on the front cover 31 and the pivoting rib 21 , so that the front cover 30 is detachably disposed on the connecting cover 20 . The first positioning unit 571 can be a member having a positioning function such as a corresponding magnet, a cooperation between the card slot and the bump. Both ends of a spring 57 are fixed to the hook body 544 at the end of the third unit 54 and the fourth surface 312 of the front cover 31, respectively. In order to facilitate the user to pull the front cover 30 to slide relative to the connecting cover 20, when the front cover 30 and the connecting cover 22 are in a flat state and the front cover 31 is connected to the pivoting rib 21, the front cover is now The front cover 31 and the pivot rib 21 are separated from each other by the first cover unit. When the spring 57 is to return to the original state to provide an elastic restoring force, the front cover 30 can be assisted to slide relative to the connecting cover 20. In other embodiments, a plurality of second positioning units (not shown) may be further included, and the second positioning unit may be a corresponding magnet, a matching of the card slot and the bump, and the like having a positioning function. The second positioning units are respectively correspondingly disposed on the third end portion 313 of the front cover 31 and the main body The fifth side 101 of the 10 is such that the front cover 31 is detachably provided to the main body 10.

Referring to FIG. 1 and FIG. 5, when the portable electronic device is in a closed state, the front cover 30 covers the fifth side 101 of the main body 10 to protect the input component 11 and the display panel 310 (please refer to FIG. 3), and the first surface 221 of the connecting cover 22 is flat on the fourth surface 312 of the front cover 31.

Referring to FIG. 2, FIG. 3 and FIG. 6 to FIG. 8 , when the portable electronic device is to be turned on in the notebook mode, the user pulls the front cover 30 to connect the front cover 30 and the connection cover. 20 is pivoted relative to the main body 10 through the opening and closing pivot assembly 40. When pivoting to the user's desired viewing angle, the input assembly 11 and the display panel 310 are exposed for the user to operate, and the front cover 31 is pivotally connected. The ribs 21 are connected by the first positioning unit 571, and the fourth surface 312 of the front cover 31 is still parallel with the first surface 221 of the connecting cover 22, and the first latch 56 abuts against the first sliding rail 513. One end of a fixed wing 512, and the second pin 55 abuts against the second slide 541 which is close to one end of the first fixed wing 512.

Referring to FIG. 9 to FIG. 12, when the portable electronic device wants to tilt the front cover 30, the user provides a pulling force of the front cover 30, and the first unit 51 is driven by the front cover 31 to make the first latch 56. Moving along the offset direction 58 toward the first slide rail 513, which is close to one end of the first fixed wing 512, the second latch 55 slides along the translation direction 59 toward the second slide rail 541 away from one end of the first fixed wing 512 until the first The latch 56 abuts against the first slide rail 513 and approaches one end of the first fixed wing 512, and the second latch 55 abuts against the second slide rail 541 away from one end of the first fixed wing 512, thereby making the first unit 51 relatively The third unit 54 translates and shifts, and the front cover 30 translates and shifts relative to the connecting cover 22, and the fifth end 321 of the rear cover 32 faces away from the connection. The direction of the first end portion 201 of the cover body 20 is moved. At this time, since the offset direction 58 is not parallel to the translation direction 59, the relative position of the pivot shaft 53 and the front cover 31 is changed, causing the front cover 31 to rise and Keep away from the effect of connecting the cover plate 22.

Referring to FIG. 13 to FIG. 17 , after the front cover 31 has been disengaged from the pivoting rib 21 , the front cover 30 can pivot relative to the connecting cover 20 , and the user pushes the front cover 30 to make the first A unit 51 drives the third unit 54 to pivot the third unit 54 relative to the second unit 52, and the connecting cover 20 also pivots relative to the main body 10 through the opening and closing hinge assembly 40, and the front cover 30 and the connecting cover An angle is formed between the bodies 20, and the frictional stagnation force provided by the hinge assembly 50, or the frictional force of the front cover 30 against the main body 10, or the second positioning unit is used to make the front cover body. The first cover portion 30 of the connection cover body 20 abuts against the fourth side of the front cover plate 31. 312 to provide support.

As shown in FIG. 18 to FIG. 21, when the portable electronic device is to be in the tablet usage mode, the user can further push the front cover 30 to make the front cover 30 relative to the connection cover. The body 20 is pivoted to pivot the front cover 30 to a maximum flip angle. At this time, the first unit 51 drives the third unit 54 to pivot relative to the second unit 52. The connection cover 20 also passes through the opening and closing hinge assembly 40. Pivoting on the main body 10, continuously pivoting to the front cover 31 covering the fifth side 101 of the main body 10 and the input assembly 11, and only exposing the display panel 310, the connecting cover 22 abutting against the fourth side of the front cover 31 312 provides a supporting force to present a tablet usage mode in which only the display panel 310 can be used, and the limiting protrusion 530 of the pivot 53 abuts against the second unit 52. Stopping the bump 524, and restricting the third unit 54 from rotating relative to the second unit 52. In the preferred embodiment, the angle between the front cover 31 and the main body 10 is an acute angle, so that the display panel is 310 is tilted upward for viewing by the user. Preferably, the angle may be between 10 degrees and 45 degrees, or may be 20 degrees for a preferred viewing angle.

Therefore, the present invention, through the arrangement of the hinge assembly 50, allows the front cover 30 to pivot relative to the connection cover 20, further switching the mode of use, and through the arrangement of the connection cover 20 to protect the hinge assembly 50 while being connected. The front cover 30, through the cooperation of the front cover 30, the connection cover 20 and the hinge assembly 50, covers the input assembly 11 to protect the input assembly 11 from pressure damage in the tablet use mode.

Moreover, after the first unit 51 slides in the translation direction 59 and the offset direction 58, the front cover 30 generates an effect of lifting and moving away from the connection cover 20 to avoid generation between the front cover 31 and the connection cover 22 during pivoting. The interference, and because the translation unit and the offset unit are not parallel, such that the distance of the first unit 51 from the pivot 53 is greater than the offset distance of the first rail 513, the first unit or the corresponding unit does not need to be raised accordingly. The three units can achieve the required lifting height, thus helping to reduce the volume of each component and thus the trend of thinning portable electronic devices.

The above is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Although the present invention has been disclosed in the above preferred embodiments, it is not intended to limit the invention, and A person skilled in the art can make some modifications or modifications to the equivalent embodiments by using the above-disclosed technical contents without departing from the technical solutions of the present invention. Any simple modifications, equivalent changes, and modifications made to the above embodiments in accordance with the technical spirit of the present invention are still within the scope of the technical solutions of the present invention.

10‧‧‧ Subject

22‧‧‧Connecting cover

312‧‧‧ fourth side

32‧‧‧ rear cover

51‧‧‧ first unit

52‧‧‧Second unit

54‧‧‧Unit 3

571‧‧‧First positioning unit

Claims (21)

A portable electronic device comprising: a main body; a connecting cover body comprising a first end portion and a second end portion, the second end portion connecting the main body, the connecting cover body being rotatable relative to the main body; a front cover body movable relative to the connection cover body; a hinge assembly connecting the first end portion of the connection cover body and the front cover body to slide and rotate the front cover body relative to the connection cover body, The hinge assembly includes: a first unit disposed on the front cover; a second unit disposed on the connection cover; a third unit pivotally connected to the second unit and disposed adjacent to the first unit The third unit pivots to the second unit to rotate the front cover relative to the connecting cover; a translation unit provides a translation direction, the translation unit connects the first unit and the third unit; The offset unit provides an offset direction, and the translation direction is not parallel to the offset direction, the offset unit is connected to the first unit and the third unit, and the first unit is configured by the translation unit and the offset The unit is opposite to the offset direction in the translational direction The third slide means so that the front cover with respect to the connecting sliding cover. The portable electronic device of claim 1, wherein when the front cover is subjected to a pulling force, the first unit drives the translation unit and the offset unit to translate the first unit relative to the third unit And offsetting, the front cover is translated and offset relative to the connecting cover body, and then, when the front cover body is When the first unit drives the translation unit, the offset unit and the third unit, and the third unit is pivoted to the second unit, the front cover forms an angle with the connection cover. The portable electronic device of claim 1, wherein the offset unit comprises a first slide rail and a first latch, the translation unit comprises a second slide rail and a second latch, wherein the first slide One of the rails is axially different from one of the axial directions of the second rail. The portable electronic device of claim 3, wherein the first slide rail has a curved shape, and the second slide rail has a straight line shape. The portable electronic device of claim 4, wherein the first slide rail is disposed on the third unit, and the first latch is disposed on the first unit and slidably disposed on the first slide rail. The second sliding rail is disposed on the first unit, and the second latch is disposed on the third unit and slidably disposed on the second sliding rail. The portable electronic device of claim 4, wherein the first slide rail is disposed on the first unit, and the first latch is disposed on the third unit and slidably disposed on the first slide rail. The second sliding rail is disposed on the third unit, and the second latch is disposed on the first unit and slidably disposed on the second sliding rail. The portable electronic device of claim 1, wherein the hinge assembly further comprises a pivot shaft that is respectively disposed through the second unit and the third unit. The portable electronic device of claim 7, wherein the pivot axis comprises an arcuate limiting bump, the second unit includes a stop bump, and the third unit pivots to the second unit At a maximum angle, the arcuate limit bumps abut the stop bumps. The portable electronic device of claim 1, wherein the main body comprises an opening and closing hinge assembly, the connecting cover body comprises a pivoting rib and a connecting cover a pivoting rib is disposed at the second end of the connecting cover, and the pivoting rib is in contact with the opening and closing hinge assembly, the connecting cover connecting the pivoting rib is connected to the pivoting rib One end of the opening and closing hinge assembly, the connecting cover plate includes a first surface and a second surface opposite to the first surface, the front cover body includes a front cover and a rear cover, the front cover includes a front cover The third surface is disposed on the fourth surface of the front cover, and the second unit is disposed on the first surface of the connection cover. The four sides of the front cover are connected to the first side of the connecting cover by the hinge assembly, so that the front cover slides and rotates relative to the connecting cover, and the rear cover is disposed adjacent to the connecting cover The fourth side of the front cover, and the rear cover and the connecting cover cover the fourth side of the front cover. The portable electronic device of claim 9, further comprising a plurality of first positioning units, wherein the first positioning units are respectively disposed on the front cover and the pivoting rib, so that the front cover is detachable It is placed off the ground in the connection cover. The portable electronic device of claim 9, further comprising a plurality of second positioning units, wherein the second positioning units are respectively disposed on the front cover and the main body, so that the front cover is detachably Set to the body. The portable electronic device of claim 1, wherein the body comprises a fifth side, and the fifth side is provided with an input component. The portable electronic device of claim 9, wherein the third surface is provided with a display component. A hinge assembly includes: a first unit; a second unit; a third unit pivotally connected to the second unit and disposed adjacent to the first unit a third unit pivoting to the second unit; a translation unit providing a translation direction, the translation unit connecting the first unit and the third unit; and an offset unit providing an offset direction, and The shifting direction is not parallel to the offset direction, the offset unit is connected to the first unit and the third unit, and the first unit is opposite to the offset direction by the translation unit and the offset unit along the translation direction Slide in the third unit. The hinge assembly of claim 14, wherein when the first unit is subjected to a pulling force, the first unit drives the translation unit and the offset unit to translate and offset the first unit relative to the third unit Then, when the first unit is subjected to a thrust, the first unit drives the translation unit, the offset unit and the third unit, and the third unit is pivoted to the second unit, and the third unit The unit forms an angle with the second unit. The hinge assembly of claim 14, wherein the offset unit comprises a first slide rail and a first latch, the translation unit comprises a second slide rail and a second latch, wherein the first slide rail The axial direction is different from one of the axial directions of the second slide rail. The hinge assembly of claim 16, wherein the first slide rail has a curved shape, and the second slide rail has a straight line shape. The hinge assembly of claim 17, wherein the first slide rail is disposed on the third unit, the first latch is disposed on the first unit and slidably disposed on the first slide rail, the second slide The rail is disposed on the first unit, and the second latch is disposed on the third unit and slidably disposed on the second slide rail. The hinge assembly of claim 17, wherein the first slide rail is disposed on the first unit, the first latch is coupled to the third unit and slidably The second slide rail is disposed on the third slide unit, and the second slide rail is coupled to the first unit and slidably disposed on the second slide rail. The hinge assembly of claim 14, further comprising a pivot shaft that is respectively disposed through the second unit and the third unit. The hinge assembly of claim 20, wherein the pivot shaft comprises an arcuate limit projection, the second unit includes a stop projection, and the third unit pivots to the second unit to a maximum At an angle, the arcuate limit projection abuts the stop bump.