The invention relates to an arrangement on a spreader which is operative for lifting containers, the arrangement comprising a flipper arm which is supported at the corner of the spreader such that the flipper arm is pivotable between an upraised rest position and a lowered operative position wherein the flipper arm is effective for positioning of the spreader corner relative to the corresponding corner of a container upon connecting the spreader to the container, in accordance with the preamble of claim 1.
Flipper arm is the technical term used in the subject trade as a definition for the arms that are pivotally arranged in the corners of a spreader. The flippers arms are controllable in a downwards pivoted motion so as to extend below the spreader and in the lowered position effective for guiding the spreader upon lowering towards the top side of the container, in the connection of the spreader to the container's corner fittings through connecting means fitted to the spreader. Such flipper arms are typically associated with piston/cylinder units that are supplied from a hydraulic power system that is continuously pressurized for powering the movements of the flipper arm, as well as for holding the flipper arm in position.
A typical feature in the operation of the flipper arm is that the power needed for pivoting the flipper arm between the raised rest position and the lowered operative position may be seen as moderate, whereas the external loads on the flipper arm applied from contact with the container during positioning may be considerable, and many times the size of the power that is required for pivoting the flipper arm. For reason of security, and in order to withstand such external forces that tend to move the flipper arm away from its operative position, the flipper arm's hydraulic drive means is often oversized.
The present invention aims to provide a flipper arm drive that it designed to protect the powering system against loads resulting from the flipper arm's contact with the container and from lateral movements of the spreader relative to a container in connecting operations.
This object is met through the arrangement defined in accompanying claims.
Briefly, through the present invention there is provided an arrangement on a spreader comprising a flipper arm which is supported at the corner of the spreader such that the flipper arm is pivotable between an upraised rest position and a lowered operative position wherein the flipper arm is effective for positioning of the spreader corner relative to the corresponding corner of a container upon connecting the spreader to the container. The arrangement is characterized in that the flipper arm is carried on a rotatable shaft and driven by a motor, and wherein a power transmission is inserted between the motor and the flipper arm, the power transmission being effective for the transfer of torque from the motor to the flipper arm upon energizing the motor, and operative for locking the flipper arm in its pivoted position upon non-energizing the motor.
In the preferred embodiment, the power transmission between the motor and the flipper arm comprises a self-locking worm drive including a worm screw driven by the motor and tangentially engaged by a gear-wheel carried on the flipper arm shaft, wherein the pitch of threads are chosen to permit the gear-wheel to be rotated by the worm screw while preventing the worm screw from being rotated by the gear-wheel.
In addition, a parking brake may be included between the motor and the flipper arm and arranged to be de-activated upon energizing the motor, and activated upon non-energizing the motor.
Through the measures mentioned above there is provided, between the motor and the flipper arm, a power transmission which permits the use of electrical motors for powering the flipper arm's pivot motion between the rest and operative positions, respectively.
Further advantageous features and embodiments are defined in the subordinated claims.
The invention is further explained below with reference to the accompanying, diagrammatic drawings, wherein
In
For guidance of the spreader during connection operation, arms or flipper arms 5 are pivotally arranged in the spreader corners. A flipper arm 5 is pivotable between an upraised rest position and a lowered operative position, wherein the flipper arm extends below the spreader and adjacent a side of the container in order to position and guide the spreader upon lowering towards a top side of the container (the lowered position of a flipper arm 5 is illustrated through a dash-dotted line in
With reference to
The motor may be a hydraulic motor. However, the motor advantageously is an electric motor which is preferred for environmental reasons and with respect to maintenance. In both alternatives, the power transmission between the motor and the flipper arm is arranged in such way that the motor is dimensioned merely to provide the power that is required for pivoting the unloaded flipper arm by rotation of the shaft 9. More precisely, the power transmission is arranged to absorb any external load applied to the flipper arm, and to prevent such loads from being transferred back to the motor. In other words, the motor 17 is effective for rotation of the flipper arm only but non-effective for holding the flipper arm in its pivoted position, whether the flipper arm is lowered to its operative position or raised to its rest position. This means, in the case of an electromotor, that the power supply may be shut off when the flipper arm has reached its position, and in the case of a hydraulic motor it means that hydraulic pressure is not required for holding the flipper arm in its pivoted position.
The power transmission according to the invention may have an electrically controllable parking brake (not shown) inserted between the motor and the flipper arm. E.g., a brake may be realized as a disc brake having discs of radial extension connected to the motor's power shaft or to the worm screw, or connected to the flipper arm's shaft. Spring biased brake blocks are controlled through electro-magnets to hold the discs in arrested position through frictional engagement until the magnets are energized to release the discs from engagement with the brake blocks, against the force of the springs. The electromagnets are activated upon supply of current for rotation of the flipper arm, and are non-activated for applying brake force to the discs upon cease of current supply. A hydraulically activated brake may be arranged in the power transmission between the motor and the flipper arm in an analogous way.
As preferred, the power transmission is arranged as illustrated to have an irreversible or self-locking worm drive wherein the pitch of threads in worm screw and gear-wheel are chosen to prevent rotation of the worm screw 12 when a load is externally applied to the flipper arm. Irreversible reduction gears are known per se and are used in different connections, such as in vehicle steering, to prevent external forces from being transferred back through the power transmission and to apply load to the power supply system. In the subject application, the operation of the self-locking worm drive is used to unload the motor and to protect the motor from damaging forces, while simultaneously resulting in a reduction of motor effect and size which may be dimensioned to provide the reduced power that is required for pivoting of the flipper arm only. The self-locking worm drive of the illustrated embodiment may alternatively, as desired, be operated in combination with a parking brake. This may, e.g., be called for in order to counteract a play possibly occurring in the engagement between the gear-wheel and the worm screw.
The invention is defined through the characterizing features of the accompanying claims, the same being construed to encompass the embodiments illustrated above and any modification thereof that, from this description, is derivable by a person skilled in the art.
Number | Date | Country | Kind |
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0600092-1 | Jan 2006 | SE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/SE07/00026 | 1/15/2007 | WO | 00 | 1/13/2009 |