Note: Descriptions are shown in the official language in which they were submitted.
CA 02273558 2001-10-02
1 Now, there is a potential for the cables or lifting spring means to part or
2 fail. If the door is being raised or lowered, this can result in the door
dropping
3 and injury or damage may follow.
4 Safety brake mechanisms have been marketed and patented for
stopping the door from falling when tension in the cable is lost. See United
6 States Patent 5,291,686, issued to Sears et al, and brochures made of record
7 herewith, as examples of this prior art.
8 These known safety brake mechanisms typically involve the following
9 components:
~ a bracket is secured to the lower corner of the door;
11 ~ the bracket supports a horizontal shaft having a partly toothed disc
12 at one end;
13 ~ the disc is positioned within the track. The disc has a smooth
14 portion which is in contact with the track so that the disc can glide
along the track when the door is in motion. Otherwise stated, the
16 disc functions as a bottom roller for the door;
17 ~ an arm protrudes from the shaft - the arm has an eye for engaging
18 the lifting cable;
19 ~ a torsion spring is positioned around the shaft. The spring is
anchored at its inner end to a lug attached to the bracket. At its
21 outer end the spring is connected with the shaft.
3
CA 02273558 2001-10-02
1 As long as the cable is taut, the arm is restrained by the cable. The spring
is
2 torqued and ready to unwind, but it is prevented from unwinding by its end
3 connections with the lug and shaft. When the cable breaks, the arm is
4 released, the spring rotates the shaft and disc and drives the teeth into
the
guide track to brake the door and prevent it from dropping.
6 These known safety brake mechanisms have been associated with
7 problems which have affected acceptance in the market place.
8 It needs to be understood that there are three different main types of
9 overhead door systems. The first system is referred to as a "standard lift".
In
this system the door goes immediately into an overhead position as soon as it
11 begins to lift off the floor. The lift cables are initially in tension in
an amount
12 equal to the total door weight. This initial tension gradually decreases
almost
13 to zero once the door is fully open and entirely horizontal. The second
system
14 is referred to as a "hi-lift" assembly. In this case, the door travels
upwardly for
a pre-determined distance before it begins to travel overhead or horizontally.
16 The lift cables are initially in tension equal to the door weight. This
initial
17 tension gradually decreases to equal that portion of the door weight which
has
18 not travelled overhead once the door is fully open. In the third system,
19 referred to as the "vertical lift" system, the door travels upwardly
without
travelling overhead. Therefore the lift cables remain in tension at all times
in
21 an amount equal to the total door weight.
4
CA 02273558 2001-10-02
1 In other words, with the standard lift system the cable tension is greatly
2 reduced when the door is fully open, particularly if the door is small and
light,
3 whereas the cables in the hi-lift and vertical lift systems always retain
4 appreciable tension when the door is fully open. The known safety brakes
work adequately for the hi-lift and vertical lift systems in some situations.
6 However they are unreliable with the standard lift doors because the torsion
7 spring is liable to unwind slightly when the cable is untensioned, causing
the
8 teeth to engage the track in a braking action. This is, of course,
undesired.
9 Another problem can arise in situations where an electrically operated
motor drives a shaft which carries drums on which the lift cables are wound or
11 unwound. When the electric motor is first started, it has a tendency to
cause
12 some slack to arise in the lift cables, which again can undesirably cause
the
13 brake to set. This is particularly likely to occur with the standard lift
doors.
14 It is therefore an objective of the invention to provide a safety brake
mechanism wherein the tension in the torsion spring can be adjusted to
16 optimize or match the spring to the door assembly with which it is being
used,
17 to thereby reduce the likelihood of undesired triggering of the braking
action.
18 For purposes of this description, "outer" denotes furthest from the
19 center of the door, "inner" denotes closest to the center of the door,
"rearward"
denotes toward the door surface and "forward" denotes away from the door
21 surface.
5
CA 02273558 2001-10-02
1 SUMMARY OF THE INVENTION
2 In accordance with a preferred form of the invention, a safety brake
3 mechanism is provided comprising:
4 ~ a bracket for mounting to one lower corner of an overhead sectional
door, the bracket having a central web and inner and outer
6 forwardly protruding, parallel legs;
7 ~ a roller shaft mounted to the legs and carrying a rotatable roller on
8 its outer end for running in the adjacent door guide track, the shaft
9 further carrying a sheave, spaced inwardly from the roller, around
which the lifting cable may extend;
11 ~ the bracket having an upwardly extending section carrying means
12 for anchoring the free end of the lifting cable;
13 ~ a brake shaft, rotatably mounted to the legs above and forwardly of
14 the roller shaft, the brake shaft being positioned to clear the forward
end wall of the track and to be forwardly spaced therefrom;
16 ~ the brake shaft carrying a cam member having at least one
17 downwardly and rearwardly directed tooth, for engaging the outer
18 surface of the forward end wall of the track, and an arm having an
19 eye through which the anchored end of the cable extends as it
passes around the sheaves
21 ~ the brake shaft carrying a torsion spring secured at its outer end to
22 spring-anchoring means attached to the shaft and at its inner end to
23 spring-tensioning means secured to the inner leg of the bracket.
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1 The resulting assembly is characterized by:
2 ~ the utilization of two spaced apart shafts, the rear shaft carrying the
3 roller for controlling the positioning of the door, bracket and braking
4 teeth relative to the track, the forward shaft locating the cam
member and teeth outside the track and ensuring that the
6 positioning of the teeth is fixed relative to the roller, so that
7 improved clearance is created and the teeth are better kept from
8 contacting the track at its curve;
9 ~ the cam member functioning to bring the teeth into contact with the
track in an angular position so that the door weight will then drive
11 the teeth firmly into the track with a wedging biting action, when the
12 torsion spring is released; and
13 ~ the utilization of a tensioning device on the brake shaft, for varying
14 the tension of the spring to better match it with the type of lift
involved and the weight of the door used.
16 Broadly stated, the invention comprises, in combination, an overhead
17 sectional door, having a side edge and bottom corner; a guide track mounted
18 beside the door for guiding the door, said track having a front end wall; a
19 tensioned lift cable for lifting the door from the bottom corner; and a
safety
brake mechanism comprising a bracket attached to the lower corner of the
21 door adjacent the track; a roller shaft having inner and outer ends, the
roller
22 shaft being mounted to the bracket and carrying a rotatable roller at its
outer
23 end, the roller being positioned to run in the track, a brake shaft having
a
24 longitudinal axis and inner and outer ends, the brake shaft being rotatably
7
CA 02273558 2001-10-02
1 mounted to the bracket so that it is adapted to rotate about its axis
between
2 non-braking and braking positions, the outer end of the brake shaft having a
3 cam member secured thereto, the cam member having at least one
4 downwardly and rearwardly directed tooth at its outer end, operative to
angularly engage the front end wall of the track with a wedging biting action
6 when the brake shaft rotates to the braking position; an arm protruding
7 upwardly from the brake shaft inwardly at the cam member and having means
8 for engaging with the lift cable, a torsion spring mounted on the brake
shaft,
9 means, rotatably mounted on the brake shaft and being connected with one
end of the torsion spring, for adjusting the tension of the spring, said means
11 being disengagably secured to the bracket to affix said one spring end,
means
12 for affixing the other end of the torsion spring to the brake shaft, the
brake
13 shaft being positioned upwardly and forwardly of the roller shaft so that
the
14 roller is positioned in the track and the teeth are positioned outside and
forwardly of the track, so that the spring will normally urge the brake shaft
to
16 rotate to bring the teeth into angular engagement with the track front end
wall
17 but the arm will prevent such rotation as long as the lift cable with which
it is
18 engaged is tensioned.
8
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1 DESCRIPTION OF THE DRAWINGS
2 Figure 1 is a perspective front view of the brake mechanism, showing
3 the lifting cable in the normal tensioned state;
4 Figure 2 is a side view, partly broken away, showing the mechanism
with lifting cable in the tensioned state and the brake teeth in a non-braking
6 position;
7 Figure 3 is a side view similar to Figure 2, however the lifting cable is
8 now loose and the braking teeth have assumed the braking position; and
9 Figure 4 is a front view of the mechanism with the lifting cable in the
tensioned or taut state.
11
12 DESCRIPTION OF THE PREFERRED EMBODIMENT
13 The brake mechanism 1 comprises a bracket 2 having a central web 3
14 and inner and outer legs 4,5. The legs 4,5 protrude from the web 3 in
spaced
apart, parallel relationship. The bracket 2 further comprises an upwardly
16 projecting plate 6 having an inwardly projecting side edge portion 7 and a
17 main portion 8. A forwardly projecting portion 9 extends from the main
portion
18 8, for anchoring the free end 10 of the lift cable 11 with nut and bolt
assembly
19 12. The bracket 2 is mounted to the lower corner 13 of sectional door 14.
The bracket edge portion 7 abuts the side edge of the door 14; the main
21 portion abuts the front surface of the door.
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1 A horizontal roller shaft 15 is mounted to the bracket legs 4,5 and is
2 retained in place by cotter pin 16. A roller 17 is rotatably carried on the
outer
3 end 15a of the shaft 15. A sheave 18 is carried by the shaft 15 inwardly of
the
4 roller 17.
The roller 17 is positioned to run in the guide track 23 extending
6 alongside the side edge of the door 14.
7 A brake shaft 20 is rotatably mounted to the bracket legs 4,5 and is
8 retained in place by cotter pin 21. The brake shaft is free to turn in the
9 openings formed in the legs 4,5, through which it extends.
The brake shaft 20 is positioned forwardly of and upwardly from the
11 roller shaft 15. Its outer end 20a is clear of and spaced forwardly from
the
12 front surface 22 of the track 23.
13 An anchoring pin 25 extends through the brake shaft 20, inwardly of
14 the bracket outer leg 5. A cylindrical torsion spring 26 is mounted on the
brake shaft 20 between the legs 4,5. The outer end 26a of the spring is
16 anchored to the pin 25. The inner end 26b of the spring is anchored to a
17 spring-tensioning ring 27 screw-threaded on to the threaded end 20b of the
18 shaft 20. The ring 27 can be rotated as required to tension the torsion
spring
19 26 to a desired extent. Once set, it is locked to the inner leg 4 by nut
and bolt
assemblies 28.
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1 A tooth/cam assembly 30 is secured to the outer end 20a of the brake
2 shaft 20. The assembly 30 comprises a cam member 31 carrying teeth 32
3 aligned with the track 23. The teeth 32 extend downwardly and rearwardly
4 toward the front surface 22 of the track 23.
An arm 33 extends upwardly and rearwardly from the support member
6 31 and has an eye 34 at its upper end. The cable free end 10 extends around
7 the sheave 18, through the eye 34 on the arm 33 and is secured to the
8 bracket portion 9 by the nut and bolt assembly 12.
9 In use, the arm 33 is normally fixed by its attachment to the cable free
end 10. In this condition, the teeth 32 are retained in a non-braking
position,
11 out of contact with the front surface 22 of the track 23. However, when the
12 cable breaks, the spring 26 turns the brake shaft 20 and cam member 31
13 clockwise to bring the teeth 32 into angular engagement with the track 23.
14 The weight of the door 14 will then drive the teeth 32 into the track 23
with a
wedging biting action, as illustrated in Figure 3. The stop 36 limits the
extent
16 of rotation of the arm 33.
17 The invention utilizes two shafts, mounted to the bracket, to enable and
18 maintain the spacing of the teeth relative to the track. It further uses
the
19 released spring, rotatable brake shaft and cam member to bring the teeth
into
a wedging, angular position against the track, so that the weight of the door
21 will cause the teeth to bite into the door. And it further uses the spring-
22 tensioning ring to adjust the tension of the torsion spring so that it is
tailored to
23 the weight of the door.
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1 While the foregoing description sets forth applicant's best mode of the
2 invention, it will be apparent to those skilled in the art that various
3 modifications may be made to the invention without departing from the spirit
4 and scope of the invention.
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