BACKGROUND OF THE INVENTION
Telescoping cranes having extendable arms are used for film production, equipment inspection, construction, and other applications. The payload is placed at the front end of the crane arm. Relative to camera cranes, the payload is often a remotely steered camera mount or camera head supporting a camera. In other applications the payload may be an inspection sensor, a paint spray nozzle, or other tool or device. Typically, the weight of the payload is initially counterbalanced by manually adding or removing counterweights to or from the back end of the crane arm. A counterbalance weight carrier or tray automatically moves rearwardly as the crane arm telescopically extends forward. The center of mass of the crane arm and the payload remains at the axle or pivot point of the crane arm, regardless of the telescoping extension and retraction of the crane arm. Consequently, the crane arm remains balanced. However, if the position of the payload relative to the crane arm changes, for example, if the payload rotates, or moves in the front/back direction relative to the crane arm, the crane arm may become unbalanced. Accordingly, there is a need for a telescoping crane arm that can remain balanced, regardless of the changes in payload position and/orientation.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings, the same reference number indicates the same element in each of the views.
FIG. 1 is a side view of a telescoping camera crane.
FIG. 2A is a schematic diagram of a first embodiment of a telescoping crane arm with a payload in a first position and a counterweight carrier in a first position.
FIG. 2B is a schematic diagram of the telescoping crane arm of FIG. 2A with the payload in a second position and the counterweight carrier in a second position.
FIG. 2C is a schematic diagram of a telescoping crane arm of FIG. 2A with the payload in a third position and the counterweight carrier in the first position.
FIG. 3A is a schematic diagram of a second embodiment of a telescoping crane arm with a payload in the first position and a counterweight carrier in a first position.
FIG. 3B is a schematic diagram of the telescoping crane arm of FIG. 3A with the payload in a second position and the counterweight carrier in the first position.
FIG. 3C is a schematic diagram of the telescoping crane arm of FIG. 3A with the payload in a third position and the counterweight carrier in the first position.
FIG. 4 is a top view of the third embodiment.
FIG. 5 is a side view of the embodiment of FIG. 4.
DETAILED DESCRIPTION
An improved telescoping crane arm maintains the center of balance about the crane arm axle or pivot point even with changes in the position of the local center of mass of the payload, without any input from the crane operator. This is performed via a mechanism or linkage which adjusts the position of the counterweight carrier to compensate for the shift in the local center of mass of the payload. For example, a linear actuator may be integrated with the counterweight carrier cable system that adjusts the neutral position of the counterweight carrier. An independent servo system may control the position of the counterweight carrier.
The payload can be placed on an adjustable mount that can be changed by a controller, directed manually by a human operator, or automatically via computer controller. Moving the adjustable payload mount adjusts the center of mass of the system, i.e., the combination of the crane arm and the payload.
As one example, the drawings show the invention as used on a telescoping camera crane. However, the invention may of course also be used on other types of telescoping cranes as well. FIG. 1 shows a camera crane 30 having a fully extended telescoping crane arm 35 mounted onto a mobile base 32, as described in U.S. Pat. No. 8,251,599 B2, incorporated herein by reference. The mobile base 32 may be a truck or road vehicle, or a motorized special purpose camera crane base or dolly. Typically, the mobile base 32 has an internal combustion motor and/or electric motors which drive the wheels 34, optionally with all-wheel drive and/or all-wheel steering. Smaller cranes may be moved by manually pushing an unmotorized mobile base or dolly.
A first section or outer tube 52 of the crane arm 35 is mounted on tilt axle stubs 70 in a U-shaped frame 46, which is rotatably mounted on a column 36, so the crane arm 35 can move in the tilt and pan axes. A second section or tube 54 is mechanically linked to a counterweight carrier 50 which is movable along the top of the first section 52 of the crane arm 35. A third section or tube 56 is mechanically linked to the second section 54. An actuator drives the tube sections 54 and 56 in the front/back direction on the first section 52. As the tube sections 54 and 56 telescopically extend forward, the counterweight carrier moves backwards, and vice versa, to keep the crane arm balanced. Additional inner tubes may be used, to provide greater telescoping distance. Typically, the counterweight carrier 50 is mechanically linked to the second section or inner tube 54 via cables extending around pulleys inside of the outer tube 52. As a result, the counterweight carrier 50 and the telescoping sections of the crane arm 35 automatically move in opposite directions, but they cannot move independently of each other.
Relative to camera cranes, the payload 60 may be a camera mounted on a remotely controlled camera head attached to the front end of the crane arm 35 at a pivot mount 80. The camera head typically has a camera platform movable at least in a tilt axis and a pan axis. Some camera heads also have roll axis movement. One or more electric pivot motors 88 can pivot or rotate the payload through various payload angles, from the head down position shown in FIG. 2A to or through the head center position shown in FIG. 2B, and into the head up position shown in FIG. 2C.
The electric pivot motors are typically contained within the camera head and are remotely controlled by the camera crane operator. Referring to FIGS. 2A, 2B and 2C, the pivoting movement of the camera head or payload 60 changes the center of mass of the combined crane arm 35 and payload 60, i.e. the balanced system 30, causing it to become unbalanced. Specifically, in FIG. 2B, the local center of mass of the payload 62 is shifted forward from its position in FIGS. 2A and 2C. The movement of the counterweight carrier 50 compensates for the telescoping extension and retraction of the crane arm 35, but not for the unbalanced condition resulting from the pivoting movement of the payload 60. Thus, in conventional telescoping cranes movement or rotation of the payload causes the crane to become unbalanced. The unbalanced condition can result in unexpected tilt up or tilt down movements, potentially creating a hazard operating crews and equipment.
The improved telescoping camera crane 30 shown in the Figures overcomes this problem by applying a rectifying or corrective torque to the crane arm 35 about the pivot axle 70 to compensate for both imbalance due a shifting payload, and for the telescoping crane sections. This can be achieved in several different ways.
In a first embodiment, sensors 82 and/or 84 electrically connected to the computer controller 40 measure the mass (or weight) of the payload 60 and the payload angle AA of the payload relative to the crane axis BB. Using these sensor outputs, the computer controller calculates the position of the local center of mass 62 of the payload. The sensors 82 and/or 84, or an alternative sensor, also detects the extension of the crane arm 35, or the extension is maintained in a memory of the computer controller 40. The distance to the local center of mass 62 of the payload to the pivot mount 80 is known or measured and used as an additional input to the computer controller 40. The computer controller 40 may perform a calibration procedure to calculate the distance to the payload's center of mass from the payload pivot mount 80. This calibration involves pivoting the payload 60 through a range of motion and measuring the torque required to maintain the orientation of the payload 60 relative to the crane arm 35 and the direction of gravity.
In the embodiment of FIGS. 2A, 2B and 2C, the computer controller 40 controls a first actuator 58 to move the counterweight carrier 50 to a position which maintains the system 30 in balance. The actuator may be a linear actuator, as in U.S. Pat. No. 8,251,599, or a rotary actuator 102 as shown in FIG. 5, and described in U.S. Pat. No. 10,146,108, incorporated herein by reference. The first actuator 58 may be mechanically linked to the counterweight carrier 50 via a cable or a chain, a lead screw, rack and pinion, etc. In the design of FIGS. 2A, 2B and 2C, unlike in U.S. Pat. Nos. 8,251,599 and 10,146,108, the counterweight carrier 50 is not mechanically linked to the second section 54 (or any of the sections). Thus, movement of the counterweight carrier 50 by the first actuator 58 is independent of the telescoping movement of the crane arm 35. Specifically, telescoping movement may be provided via second, separate actuator 64 mechanically linked to the second section 54. In this case, the computer controller may separately control and drive the first actuator 58 which only moves the counterweight carrier 50, and the second actuator 64 mechanically linked to the second section 54 (or other section(s)) to provide telescoping extension and retraction movement.
Referring to FIGS. 3A, 3B and 3C, in this embodiment, a payload system 55 is configured to compensate for an imbalance caused by a shift in the position of the payload 60. The payload system 55 includes an electric axle motor 90, sensors 82 and/or 84, electrically connected to the computer controller 40. The sensor(s) detect a shift in position of the payload center of mass 62. Based on input from the sensor(s), the computer controller 40 controls the electric axle motor 90 to apply a rectifying torque to the crane arm 35 at the tilt axle 70 to compensate for the imbalance due to the payload pivoting or moving relative to the crane arm, as shown in FIGS. 3A, 3B and 3C. The payload system 55 can be retrofit onto existing telescoping cranes, such as described in U.S. Pat. No. 8,251,599, and similar telescoping camera cranes. In this case, the existing counterweight carrier and linkage to the tube sections 54 and 56, or 115, maintain the crane arm in balance as the crane arm telescopically extends or retracts, as with conventional telescoping camera cranes, while the payload system 55 independently compensates for imbalance from a shift in position of the payload. The electric axle motor 90 may be linked to the crane arm 35 through a gear reduction. An electronic or a manual tilt axis brake may be used to temporarily hold the crane arm at a fixed tilt angle, i.e., the angle between the longitudinal axis of the crane arm and the ground as shown in FIG. 1.
In an alternative design the payload system 55 may have an electric axle motor 90 which by itself, exerts torque on the crane arm to keep the crane arm in balance. In this case, no counterweight carrier is used or needed. The present concepts may also be used to balance a crane arm (fixed length or telescopic) subject to balance shifting events, such as a change in the weight or longitudinal position of the payload, buoyancy forces if the payload is immersed in water, accessories placed onto the crane arm, etc.
FIGS. 4 and 5 show a crane 100 having a single telescoping section or inner tube 115. The ends of a belt (or a chain) 104 are attached to opposite ends of a primary counterweight carrier 50. The belt 104 extends around a sprocket driven by a first actuator or electric motor 102. The back end 117 of the inner tube 115 is attached to the belt 104. Counterclockwise rotation of the electric motor 102 drives the inner tube 115 forward with the inner tube 115 telescopically extending out of the outer tube 113. A payload system 112 includes a secondary counterweight carrier 114 is movable on the top of a primary counterweight carrier 50 between the front and back positions shown in FIG. 5. Sensors 82 and/or 84 electrically connected to the computer controller 40 measure the local center of mass of the payload 60. The computer controller 40 controls the electric motor 102 which extends and retracts the inner tube or section 115 and simultaneously moves the primary counterweight carrier 50 to compensate for the extension/retraction of the inner tube or section 115. The computer controller 40 also controls a second actuator 116 attached to the secondary counterweight carrier 114, to position the secondary counterweight carrier 114 at a position which compensates for a change in position of the local center of mass of the payload 60. The secondary counterweight carrier 114 may optionally roll on tracks 118.
From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the scope of the invention. Accordingly, the invention is not limited except as by the appended claims.
Patent Application
20240400353
