Battens often need to be lowered for exchanging and servicing the suspended equipment. One of the most common and least expensive batten elevating systems is a counterweighted carriage, which includes a moveable counterweight for counterbalancing the batten and equipment supported on the batten. The counterweights reduce the effective weight of the battens and any associated loads.
But a typical counterweight system represents a significant cost. It may take three weeks to create a counterweight system that accommodates a height of 70ft and depth of 30 feet.
And typical counterweight systems may not be foolproof. In a sandbag counterweight system, the locking device is merely a rope tied off to a stage mounted pin rail, while the overload limit is regulated by the size of the sandbag. In this rigging design, however, a number of additional bags can be added to the set of rope lines, and thereby exceed the safe limit of suspension ropes and defeat the overload-limiting feature.
Another common hoisting system employs a winch to raise or lower the battens. Hand operated winches can occasionally free run when heavily loaded and can then drop the suspended load, a major safety hazard. Other types of hand winches use a ratchet lock, but again these winches are also susceptible to free running when they are heavily loaded and hand operated.
Therefore, the need exists for a lift assembly that can replace traditional counterweight systems.
The lift assembly of the present invention employs a modular frame for accommodating a different number of head blocks. The lift assembly also includes a modular drum construction which allows for the ready and economical configuration of the system to accommodate various stage sizes.
The frame 20 is a rigid skeleton to which the drum 160, the drive mechanism 100 and the head block 80 are attached. The frame 20 is constructed to be connectable to the building.
The lift assembly 10 is constructed to work with at least one cable 14. Typically, the number of cables is at least four, but may be as many as eight or more. A cable path extends from the drum 160 through a corresponding head block 80 to pass about a loft block 220 and terminate at the batten 12.
Each head block 80 draws cable 14 from a corresponding winding section along a tangent to the drum 160. The angle between the head block 80 and the respective cable take off point from the drum 160 may be repeated by each of the head blocks 80 relative to the drum.
As the head blocks 80 are mounted to the head block mount 30, the head blocks can overlap along the axis of drum rotation. The overlap allows for size reduction in the lift assembly 10. That is, a helical mounting of the head blocks 80 allows the head blocks to overlap radially as well as longitudinally relative to the axis of drum rotation. By overlapping radially, the plurality of head blocks 80 can be operably located within a portion of the drum circumference, and preferably within a 908 tk arc. Thus, the operable location of the head blocks 80 can be accommodated within a diameter of the drum. By disposing the head blocks within a dimension substantially equal to the diameter of the drum 160, the frame 20 width can be reduced to substantially that of the drum diameter.
In one design, the drive shaft 114 includes a threaded drive portion. This threads into a keeper 115, which in turn is connected to the frame 20. Referring to Fig. 2, rotation of the shaft 114 not only rotates the drum 160, but the drum translates to the left or the right relative to the frame 20 and hence relative to the attached head blocks. As the drive mechanism 100 is attached to the drum 160 and attached to the frame 20 along a linear slide 111, the drive mechanism also translates along the axis of drum rotation relative to the frame.
By longitudinally translating the drum 160 during unwinding and winding rotation, the fleet angle for each head block 80 and corresponding take off point in the winding section 162 is maintained. That means there is no need for a movable connection between a plurality of head blocks 80 along the helical mount and the frame to maintain a desired fleet angle.
The drum 160 includes at least one winding section 162. The number of winding sections 162 corresponds to the number of cables 14 to be controlled by the lift assembly 10. As shown in FIG. 2, there are seven winding sections 162 on the shown drum. Each winding section 162 is sized to retain a sufficient length of cable 14 to dispose a connected batten 12 between a fully lowered position and a fully raised position.
The lift assembly of the present invention includes a load brake for reducing the risks associated with drive or motor failures.
The load brake 130 is located mechanically between the drum 160 and the gearbox 120, as shown in Fig. 3. The brake includes a drive disc 132, a brake pad 134, a driven disc 136, and a peripheral ratchet 138, a tensioning axle 140 and a tensioning nut 146.
The drive disc 132 is fixed to the drive shaft 114. The drive disc 132 includes a concentric threaded coupling 133. The driven disc 136 is fixed to the drum 160. The driven disk is also fixed to the tensioning axle 140 that extends from it. The tensioning axle has a set of braking threads 141 and, at the other end, a set of tensioning threads 143. The brake pad 134, friction disc, is set around the tensioning axle 140 between the drive disc 132 and the driven disc 136. The brake pad also includes a peripheral ratchet 138 that engages with a pawl 139.
The braking threads 141 engage the threaded coupling 133 of the drive disc 132. The tensioning nut 146 engages the tensioning threads 143. The brake pad 134 is thus located between the drive disc 132 and the driven disc 136 to provide a friction surface to each of the discs.
When the motor raises the load, the braking threads 141 screw into the corresponding threaded coupler 133 on the drive disc 132, thereby causing the driven disc 136 and the drive disc 132 to compress the brake pad 134. The drive disk 132, the brake pad 134 and the driven disc 136 thus turn as a unit as the cable 14 is wound upon the drum 160.
To lower or unwind cable 14 from the drum 160, the motor and hence drive disc 132 rotate in the opposite direction. Once started, the pawl catches on the ratchet to prevent rotation of the brake pad. The breaking threads 141 unscrew, pushing the drive disc and the brake pad apart, thus allowing the load on the drum 160 to rotate the drum in an unwinding direction. When this rotation stops, the load on the cable 14 causes the drum 160 and hence driven disc 136 to thread the braking threads 141 further into the coupler 133 against the now fixed braking pad 134 thereby terminating the unwinding rotation of the drum.
The tensioning nut 146 is used to determine the degree of release of the driven disc 136 from the brake pad 134. It can also be used to accommodate wear in the brake pad 134. The present configuration thus provides a general balance between the motor-induced rotation of the drive disc 132 in the unwinding direction and the torque generated by the load on the cable 14 tending to apply a braking force as the driven disc 136 is threaded toward the drive disc 132.
The present invention provides a turnkey lift assembly having rigging; power and control for the manipulation of battens, without requiring construction of traditional counterweight systems or relying on previously installed counterweight systems.
