Safety devices on overhead and jib cranes. Overhead crane safety devices and sensors: what and why? Lighting and signaling

Overhead electric cranes must be equipped with devices for automatically stopping the lifting mechanism and the mechanism for moving the bridge and trolley before they approach the stops, if the speed of their movement can exceed 32 m / min. These devices are called limit or limit switches.

All limit switches can be divided according to the switching method into main current switches, which open the main motor circuit, and control current switches, which open the contactor coil circuit. By design, limit switches are divided into lever (Fig. 2.53) and spindle (Fig. 2.54). When the lever switch lever deviates from the normal position, the contacts connected to it break the circuit of the main current or control current and the motor of the lever switches of the KU series and the VU spindle series. Switches KU-700 allow any order of closing contacts. Switches KU-701 are used in control circuits to limit the linear movement of cranes with small overruns, switches KU-703 - to limit the stroke of lifting mechanisms. Switches KU-704 and KU-706 are used to limit the linear movement of mechanisms with any overrun.

The body of the switch is made of cast aluminum alloy in a splash-proof design. When installed outdoors, it is recommended to protect the switches from the effects of atmospheric precipitation. A drum with cam washers is fixed inside the housing, when it is turned, the contacts of the block of cam elements are closed or opened.

Four fixed contacts and two levers with contact bridges are fixed on the insulating base of the block of cam elements. Contacts are made of silver. The springs hold the contacts closed. When the protrusion of the cam washer approaches the protrusion of the lever, the latter rotates and the contacts open.
A ratchet is installed on the shaft of switches KU-701, KU-704 and KU-706, which fixes the drive lever: in KU-701 - in the zero position, in KU-704 - in the zero and two extreme positions, in KU-706 - in the extreme provisions. In the KU-703 circuit breaker, fixation is carried out by a load suspended on the lever and a counterweight of the lever, which can be installed in various positions relative to the body. The limiting ruler serves as the influence on the switches KU-701 and KU-706. In the KU-703 circuit breaker, the camshaft is rotated and returned to its original position when the counterweight is raised or lowered, which is raised or lowered by a shelf mounted on a hook clip. The cam drum of the KU-704 switch rotates when the pin acts on the plug.

Possible positions of the levers relative to the switch cases are shown in fig. 2.55. The positions of the switches of the KU series are presented in Table. 2.5.

Switches VU-150M and VU-250M are used as terminal switches in crane movement control circuits or to limit the movement of lifting mechanisms.
The switch at the end of the path can open or close the contacts. To open the contacts, the rollers of the washers are installed in accordance with Fig. 2.56 a(when the washers are rotated clockwise when viewed from the side of the contact washers) or fig. 2.56 b(when the washers are rotated counterclockwise). The angle between the rollers is taken as the smallest (32°). Injection a rotation of the paired washers until the closing or opening of the contacts is called the working angle. The working angle can be from 12 to 300°.

The entire path of the mechanism must correspond to the selected working angle. The actuation angle (within the operating angle) for opening and closing the contacts is easily adjustable during installation. The angle of additional rotation of the washers, caused by the overrun of the mechanism, after the switch has been actuated, must not exceed 300°. Switches of the VU series have a cast aluminum case, in which there is a shaft with closing and opening washers, a lever with a contact bridge, a pawl and fixed contacts mounted on an insulating bar. The VU-150L1 switches have one circuit, and the VU-250M switches have two circuits, so the number of levers, fixed contacts, closing and opening washers is doubled. Reducers with a gear ratio of 50: 1 are built into the bodies of the VU-150M and VU-250M switches (50 revolutions of the drive shaft correspond to one revolution of the shaft with washers).

When the roller of the closing washer runs onto the ledge of the lever, the latter slowly turns and closes two fixed contacts, being held in the closed position with the help of a pawl. When the roller of the opening washer runs over the lug of the pawl, the lever is released and, under the action of the spring, instantly turns, opening the contacts.

The following requirements are imposed on the limit switches of the lifting mechanism: they must be installed so that after the load-handling body stops when lifting without load, the gap between the load-handling body and the stop is at least 200 mm, and for electric hoists - at least 50 mm.

With regard to clamshell cranes with a separate two-motor drive of the clamshell winch, the circuit for switching on the lifting limit switch must be designed so that the engine of the lifting mechanism and the clamshell closing engine are simultaneously turned off when the latter reaches the uppermost position. The limit switch of the movement mechanism must be installed in such a way that its engine is turned off at a distance to the stop equal to at least half of the braking path of the mechanism, and in gantry cranes - at least the full braking path. In the presence of mutual limiters of the travel mechanisms of overhead cranes operating on the same track, the specified distance can be reduced to 0.5 m. open door. The electrical circuit of magnetic cranes should be carried out so that the removal of voltage from the crane by the contacts of safety devices and devices does not affect the voltage of the cargo electromagnet. For cranes with a three-phase current electric drive, if any one phase is broken, the load lifting mechanism must be turned off. Contacts of devices and safety devices must work to break the electrical circuit.
The electrical control circuit of the crane motors must exclude: self-starting of the motors after the restoration of voltage in the network supplying the crane; start of electric motors not according to the given acceleration scheme; start-up of electric motors by contacts of safety devices - contacts of limit switches and blocking devices.

The input device of overhead cranes is equipped with an individual contact lock with a key, without which voltage cannot be applied to the crane. All metal structures - cases of electric motors, apparatuses, metal sheaths of cables, protective pipes that are not included in the electrical circuit, but may be energized due to insulation damage, must be grounded in accordance with the PUE.

In order to avoid damage to the crane equipment due to incorrect actions of the crane operator and to prevent accidents, auxiliary contacts are installed in the form of buttons with two breaking and two closing contacts. In general, the term "block contact" is applicable to any device that turns on and off control circuits. / On cranes to block doors and hatches, block contacts are enclosed in metal cases (Fig. 2.57). They are not used as limit switches on cranes due to their small size, but they are quite acceptable for blocking. Their cases are tightly closed, they do not allow dust and moisture to pass through, the permissible current is 6 A, the number of starts per hour is up to 300, wear occurs after 2 million starts. When closing, the door presses the auxiliary contact button and it closes the blocked section of the control circuit, thus preparing wiring diagram crane to work. Pressing the start button will now turn on the main contactor of the safety panel.

The emergency shutdown button "Stop" is installed in a conspicuous place in the control cabin. When it is pressed, the control circuit of the main contactor coil is opened and all crane motors are turned off, the brakes stop the movement of all mechanisms.

After disconnecting the main contactor - both emergency and accidental - all controllers must be put in zero position. The fastening of the auxiliary contact housing to the metal structures must be reliable, and its operation must be trouble-free.

The safety of people employed in the crane industry is also ensured by blocking devices that automatically relieve voltage from open current-carrying parts and de-energize the crane. Usually, the simplest limit switches of the VK type are used for this purpose. On electric bridge cranes, they are installed on the exit hatches from the cab, on the doors in the end railings of the galleries (Fig. 6.4).

Before leaving the cab to the crane gallery, the crane operator must turn off the main switch - de-energize the crane. If the crane operator did not turn off the switch for some reason, and there is no blocking, then this creates a danger of electric shock. The purpose of the blocking device is to eliminate this danger in such a situation.

Figure 6.4 - Blocking device at the entrance to the crane gallery

The exit from the cab to the crane bridge is through a hatch in the deck of the gallery. The switch installed on the hatch, when the lid is opened, breaks the electrical circuit and de-energizes the trolleys. The same purpose of the blocking device on the doors in the end railings of the crane galleries. The door to the cabin of the overhead crane must also be equipped with an electrical interlock to prevent the crane from operating when the door is open.

Zero blocking. All motor control schemes on cranes provide zero blocking. It allows you to turn on the line contactor and apply voltage to the controllers when all controllers are in the zero position. If this condition is not met and any of the controllers is not set to zero, then the cover panel contactor will not turn on and the mechanism will not be arbitrarily brought forward.

However, practice shows that if safety rules are violated, even if there is an automatic lock, an accident can occur.

For example, an electric overhead crane moves along the span of a workshop with castings suspended from a hook. At this time, a crane operator is coming to meet him on the crane runway to replace him. Having caught up with the crane, without any warning, he opens the door in the end fence and goes out to the gallery. What is happening? When the doors are opened, the lock is activated. The crane stops. But he moved at high speed, and the load suspended from him, due to inertia, passes due to the oblique tension of the rope, first forward, then makes the opposite movement - the load swayed. And people worked in the shop in the same span - and the accident became inevitable.

Limit switches and interlocks are only effective when not high speeds. If the speed exceeds 80 m/min, lever limit switches cannot provide reliable protection. In these cases, other traffic control systems are applied.

The Ural Polytechnic Institute has created a photoelectric hitchhiking designed to safely stop overhead cranes moving towards each other at high speed. Hitch-hiking; is activated when the cranes approach at a distance equal to the sum of the largest braking distances. This device can be used mainly in enclosed spaces. Another system for stopping cranes moving towards each other is made using radar sensors, with the help of which, when approaching a dangerous distance, the cranes are de-energized.

Bridge-type cranes must be equipped with load limiters that prevent it from being overloaded by more than 25%.

If cranes are controlled from the cab, from the console or remotely, they are equipped with a mechanical or electrical signaling device.

Despite the fact that equipment for overhead cranes is quite expensive, it is simply irreplaceable in a number of industries. Any breakdown, failure of the entire crane or its individual elements leads to the need for expensive repairs and often causes an unplanned shutdown of the entire technological process. In addition, lifting equipment is a potential source of danger for operating personnel and other people in the immediate vicinity.

To ensure safe operation, overhead cranes are equipped with the following instruments and devices:

limiters of the course of the bridge and cargo cart;
buffer devices;
limiters of the movement of the lifting mechanism;
supporting parts;
load limiters;
electric blocking of the cab door;
additional devices and safety devices.

Bridge and bogie travel limiters

To prevent the crane from derailing, the crane tracks are equipped with end stops, when the bridge approaches them, an automatic limiter of working movements is activated proactively, stopping the mechanism.

Cargo trolley of grapple bridge electric crane

Cargo trolleys are also equipped with similar automatic stop devices, which are triggered when approaching the extreme position. When calculating the moment of switching on the automatic limiter of movements, the braking distance of the mechanism is taken into account, which is indicated in the crane passport by the manufacturer.

The installation of automatic stop devices is mandatory for all electrically operated overhead cranes whose nominal travel speed of the bridge or trolley exceeds 32 m/min.

In addition, such devices are necessary when two or more cranes operate on the same crane track, or two or more trolleys operate on the same bridge. In this case, the movement limiters must prevent the collision of mechanisms.

The role of automatic stop devices is performed by limit switches that disconnect the electric motor of the mechanism from electrical network. All limit switches used on bridge cranes with electric drive are divided into lever and spindle ones. Lever limit switches are used to stop on contact with any stop. Usually they serve to limit the movement of the mechanism only in one direction, and should not prevent its movement in the opposite direction.

In the case when two cranes operate on the same crane track, their motors should automatically turn off at a distance between cranes of 0.5 m. Limit switches are short-range devices and at high speeds of movement of the mechanisms are often unable to prevent a collision.

To avoid this, apply various devices non-contact type, in particular, photovoltaic systems. Light emitters and receivers are installed on the bridges of cranes, which send a signal to the executive relay, which turns off the electric motors if the cranes are dangerously close to each other.

Buffer devices

Layouts and design of buffer devices

In order to increase the safety of operation of an overhead crane in the event of a sudden failure of limit switches or brakes, elastic buffer devices are used. They serve to mitigate possible impacts of the crane bridge or trolley on the end stops when running over them or on each other in a collision.

According to their design, buffer devices are divided into hydraulic, friction, spring and rubber; can be mounted on movable (cargo trolley or crane bridge end beams) or fixed (crane runway ends) elements. Buffers dampen energy during a sudden stop, reduce shock and dynamic loads that occur during a collision.

Hoist movement limiters

To automatically stop the lifting mechanism when the load gripping device approaches the uppermost position, a lifting height limiter is used. When the hook suspension approaches the bridge beams, a spindle or lever-type limit switch is activated, which disconnects the electric drive from the engine of the load lifting mechanism.

Support parts

In case of breakage of the running wheels, bridges and cargo bogies are provided with supporting parts designed for the maximum possible load. The supporting parts are installed at a distance of no more than 2 cm from the rails along which the crane or trolley moves.

Load limiters

After the limiter is activated and the drive motor is turned off, the load lowering motor is turned on

To prevent overloading of mechanisms and structures of lifting equipment, if possible under the conditions of a given technological process, overhead cranes are equipped with load limiters. Load limiter - a device that automatically turns off the electric drive of the lifting mechanism if the weight of the load being lifted is 25% higher than the crane's rating capacity.

After the limiter is activated and the drive motor is turned off, the load lowering motor is turned on. In some cases, devices for fixing overload display information about the actual weight of the load, which allows you to control the process of loading the crane.

To ensure the protection of operating personnel from electric shock, bridge-type cranes are equipped with a device for electrically blocking the cab hatch.

To ensure the protection of operating personnel from electric shock, bridge-type cranes are equipped with an electric blocking device for the cab hatch, as well as exit doors to the gallery and the crane maintenance platform. When these doors are opened, the device automatically removes voltage from the open current-carrying parts of the crane. The lock prevents the crane from working when the door is open. To de-energize the trolleys when opening restricted access doors, lever-type limit switches are used.

A remark should be made regarding not only this, but also all of the above safety devices. For overhead cranes with electromagnetic lifting mechanism removal of voltage from the crane by any of the safety devices should not affect the voltage of the cargo electromagnet.

Additional devices and safety devices

Overhead cranes operating outdoors are equipped with anemometers that measure the strength of the wind and give a signal to stop loading operations if the wind strength exceeds the permissible level. In addition, cranes on open racks can be equipped with anti-theft grips. Such grips, made in the form of pincers or stops blocking the travel wheels, will exclude the movement of an idle crane or its trolley under the influence of a strong wind pressure.

On all overhead cranes in without fail an audible alarm is installed (electric bells or sirens). With its help, the workers in the workshop are notified of the increased danger that arises during the operation of the crane.

Light and sound alarm in the crane driver's cab serves to inform about possible malfunctions crane or hazardous areas (approaching the end stops or adjacent crane). The main trolleys of the crane are equipped with light signaling (red lamps) showing the presence of voltage on them.

1.4. Safety devices and devices for gantry cranes and bridge loaders

Safety devices and devices for gantry cranes and bridge loaders, the requirements for their installation must comply with the Rules for the Construction and Safe Operation of Cranes, state standards and other regulatory documents.

In accordance with the Rules, gantry cranes and overhead loaders must be equipped with automatically triggered limiters of working movements: limiters for the upper and lower positions of the load gripping bodies, limiters for the movement of cranes and crane trolleys. To limit the upper and lower positions of the cargo suspension, lever and spindle type limiters, similar to those installed on overhead cranes, are widely used. Lower position limiters are usually installed when it is necessary to lower the load below the level of the head of the crane rails.

To limit the movement of cranes and loaders, as well as crane trolleys, end stops are installed at the end of the crane tracks and undercarriage rails. To prevent collision with dead-end stops in motor modes, proactive shutdown of the motors of the travel mechanisms is provided when the crane approaches the stops using limit switches and rails installed at a distance of the crane braking distance. To extinguish energy when stopped, cranes, loaders and their trolleys are equipped with buffer devices. The limit switches for the mechanisms of movement of cranes and reloaders are installed on the lower parts of the supports, and the limit switches for cargo carts are installed at the end of the undercarriage path, which is due to the condition of convenience and ease of installation of supply communications.

Gantry cranes and bridge loaders must be equipped with load limiters (for each cargo winch), if their overload is possible according to the production technology. Overhead crane load limiters should not allow overload by more than 25%.

According to the method of fixing the actual loading parameters, load limiters can be cargo, spring, torsion, lever, eccentric, electromechanical using strain gauges and electronic amplifiers.

In lever load limiters (Fig. 1.34), the force of the weight of the load G is transmitted to the two-arm lever 1 with the selected design ratio of the arms. On the other hand, the elastic force of the spring 2 acts on the lever (Fig. 1.34, a). Larger shoulder ratios require less spring force. When you try to lift the load in excess of the allowable, the balance of the lever is disturbed, the spring is deformed and the lever acts on the actuator, for example, limit switch 3 (Fig. 1.34, a).

Rice. 1.34. Scheme of the lever-type load limiter

In most cases, the transfer of force to the load limiter is carried out through a fixed leveling block 4 of the chain hoist (Fig. 1.34, b), mounted on the smaller arm of the lever, balanced by the force F of the spring. With such a loading scheme of the lever, the gear ratio of the limiter lever system increases:

In the practice of crane building, eccentric load limiters (Fig. 1.35), in which the leveling block is installed eccentrically on the axis and with lifting a load, overcoming the moment created by the weight 2, turns together with the lever 3, which acts on the limit switch 7, and in case of exceeding the limit value of the load, de-energizes the load lifting mechanism.

Rice. 1.35. Eccentric load limiter with weight balancing

When lifting the load to the nominal value, the resultant moment R (see Fig. 1.35) from the efforts in the ropes S on the eccentricity of the e axis is balanced by the weight of the weight G on the shoulder L of the lever (from the axis to the center of gravity of the weight):

R*e=G*L

With an increase in the effort in the rope in excess of the standard, the balance is disturbed, the lever turns until it affects the limit switch and the lifting mechanism is turned off.

A spring can be used as a balancing element instead of a weight. In such load limiters (Fig. 1.36), the force in the ropes 7 is transmitted to an eccentrically mounted block 5, which, when overloaded, causes the lever 4 to rotate relative to axis A, and that, in turn, overcoming the resistance of the balancing spring 2, acts on the pressure bar 1, which , in turn, acts on the limit switch 3. With an increase in the force in the rope in excess of the norm, the lifting mechanism is turned off.

The limiter is equipped with an adjusting screw 6 for adjusting the accuracy of operation.

Rice. 1.37. Torsion type load limiter with spring balancing

The torsion-type load limiters work on the same principle (Fig. 1.37), with the only difference that the balancing of the lever 1 in them is provided by the torsional elasticity of the shaft 2. The forces in the cargo ropes are transferred to the block 3, connected by rods to the lever 7, acting on the switch .

All considered designs of load limiters have a common drawback - they require the installation of springs and other elements of significant dimensions and masses, since they are installed on blocks of the lifting mechanism and are triggered by large forces in the load ropes of the lifting mechanisms.

In this regard, it is preferable to load lifting limiters that use force sensors: limiters OGP-1, ONK-Yu, OGK-1, etc. In sensors of this type, the force in the ropes is transmitted to a steel ring, the deformation of which is transmitted to the rheostat rheo- chord, which changes the resistance in limiter circuits. If the load capacity is exceeded, the drive of the load lifting mechanism is switched off. Forces on limiter sensors are transmitted from leveling or cargo blocks mounted on eccentric axles.

In terms of dimensions and compactness, a scheme is preferable in which the force sensor is installed on the cargo drum, for which one of the supports is made articulated and can be rotated when the shaft is bent, acting on the force sensor. Load limiters of this type are used in lifting mechanisms with a symmetrical load of the drum supports, i.e., with double-threaded drums.

On behalf of the Office for Boiler Supervision and Supervision of Hoisting Structures of the Gosgortekhnadzor of Russia, the All-Russian Research and Design and Technological Institute of Hoisting and Transport Engineering (VNIIPTMash) developed a pilot batch of improved load limiters of the PS-80 series for gantry cranes: PS-80B 100U1 with a lifting capacity of up to Yut, PS-80B 200UG with a load capacity of up to 20 tons and PS-80B 300U1 with a load capacity of up to 30 tons. control signals to turn off the lifting mechanism and turn on the audible alarm when the load exceeds the limit threshold. DST-K modification sensors are designed for installation under the hinged supports of cargo drums; under load, the sensor is deformed and a signal proportional to the load is generated. DST-B sensors are designed for installation in equalizing blocks of load lifting mechanisms; DST-S type sensors - in hook suspensions of cargo chain hoists.

The installation diagram of the PS-80 limiter is shown in fig. 1.38.

Strain gauge force sensor 1, structurally consisting of a thick-walled pipe with strain gauge sensors installed inside and an amplifying microcircuit, is mounted in a special hinged support 3, on which the bearing support 2 of the balancing block of the pulley system of the lifting mechanism is installed.

Rice. 1.38. Scheme of installation of load limiter PS-80

Thus, the DST sensor, constantly perceiving the force on the support from the lifted load, generates the corresponding signal, which is amplified and transmitted through the shielded cable 4 to the driver's cab 5. The relay tuning unit 6 and the logic unit 7 installed there provide a comparison of the current load with a given limit threshold and form the corresponding control signals. When the load on the load gripping body increases, exceeding the limit threshold, an audible signal turns on and the lifting mechanism is turned off.

In recent years, much attention has been paid to the problem of identifying the actual loading of cranes by taking into account their operating time. Thus, Sila Plus LLC and the VPIIPTMash Institute developed the Sirena complex system for monitoring the loading and residual life of overhead and gantry cranes. Using the system allows you to determine the initial and actual state of the supporting metal structures of the crane, and in the process of operation to control the reduction of its residual resource. Control over the loading of the crane and the reduction of its residual life is carried out using sensors of the load limiter and a block for collecting, processing and storing information. This information is stored for three years and updated each time the tap is turned on. Based on the information received, the actual loading mode, the class of use of the crane and the current value of the residual resource are calculated.

Gantry cranes and bridge loaders usually operate outdoors, have significant windward areas and are exposed to wind loads. At large values wind pressure, the brakes do not provide reliable retention of the crane from wind hijacking, so cranes must be equipped with anti-theft grippers with manual

or mechanical drive. The grips hold the cranes by means of friction forces between the side surfaces of the rail heads and the jaws of the grips.

In the anti-theft gripping device with a manual drive (Fig. 1.39), to create an anti-theft friction force, the pressing force on the rail 1 of the jaws 2 is provided by means of a screw device 3 with manual tightening. Anti-theft gripping devices are installed in the lower part of the metal structure of the crane supports 4. The disadvantage of manual grips is long time their closure, which is unacceptable during an emergency storm warning, as well as the impossibility of automating the closure process.

Rice. 1.39. Rail anti-theft grab with manual drive
Anti-theft grips with a mechanical drive have a number of design varieties. Driven anti-theft grippers with a screw-nut transmission (Fig. 1.40) are widely used.

Rice. 1.40. Driven anti-theft gripper with screw-nut transmission

The gripping levers 1 in the upper part are pivotally connected to the rollers 2, placed in the inclined grooves of the slider 3. When the slider moves under the influence of the screw pair 4, 5 from the drive 6 and the electric motor 7, the gripping levers connected in the lower part by the coupler 9 rotate, clamping the rail heads , thereby providing anti-theft friction force. To center the grip relative to the rails, side rollers 8 are provided.

Gantry assembly cranes, cranes for hydroelectric power plants, bridge loaders are usually equipped with anti-theft grippers with falling (spacer) wedges (Fig. 1.41).

The wedge 1 is lifted using a hydraulic cylinder 2 or a rope winch. The force of pressing the levers on the rail heads is provided by the weight of the wedge 1 acting on the

when lowering onto rollers 3, installed at the top of the gripping levers 4. After the force of pressing the wedge on the levers is removed, the latter return to their original position under the action of the forces of the springs 5. Anti-theft grippers of this type are installed on the bogie to ensure that the jaws of the levers constantly hit the side surfaces of the rails because they bend under load.

To dampen the energy of movement of cranes and crane trolleys, dead ends are installed at the end of the rail tracks. To reduce shock and dynamic loads during collisions, they are equipped with buffer devices, which by design can be rubber, spring, hydraulic and friction (Fig. 1.42).

Rice. 1.42. Buffer devices: a - rubber; b - spring; c - hydraulic; g - friction

Rubber buffers (Fig. 1.42, a) have a non-linear elastic force characteristic, which contributes to better energy dissipation and low recoil after a collision, but they are relatively short-lived. Spring buffers (Fig. 1.42, b), installed on heavy cranes, usually have four springs - two internal and two external. To eliminate the twisting of the springs under loading, the winding direction of each pair of them is opposite. Spring buffers are quite bulky; their work is accompanied by a significant recoil force.

This drawback is eliminated in hydraulic buffers (Fig. 1.42, c), in which the impact energy is absorbed by forcing the liquid through the annular gap 1 between the piston bottoms 2 and the rod 3. The piston is filled with working fluid and is installed in the housing 4. Impact when hitting the stop is perceived by the tip 5 and the accelerating spring 6, which transmits pressure to the piston, which, when moving relative to the body, opens an annular hole in the center of the piston, through which the working fluid flows. The rod 3 has a variable cross section, which allows you to control the rate of fluid flow and obtain the necessary law of resistance to the movement of the piston, and hence the absorption of energy.

The return stroke of the piston is provided by a return spring 7. Hydraulic buffers are more complex in design and require high manufacturability in their manufacture and maintenance.

Friction ball buffers are simpler in design (Fig. 1.42, d), in which, when the buffer rod 2, which receives the load, moves, the balls 5 fall into the conical cavity created by the inner insert 4 and the rod, and due to the friction forces between the balls, as well as between the body 1, conical surfaces and balls, the kinetic energy of the moving masses of the crane or reloader is absorbed. The reverse motion of the cones and balls is produced by a return spring 3. Such buffers are small in size, they almost completely lack recoil; they can be used to absorb the significant movement energies of cranes and material handlers.

Gantry cranes and overhead loaders, due to their design features, are subject to such a phenomenon as distortions, i.e. running or falling behind one of the sides of the crane when moving. Distortions of cranes as an undesirable phenomenon, causing increased loads on the metal structure and mechanisms, are due to a number of reasons: deviation from the design dimensions of the elements of mechanisms, metal structures and crane tracks, differences in the mechanical characteristics of electric motors, external climatic factors, etc.

Therefore, gantry cranes and bridge loaders must be designed for the maximum possible skew force that occurs during their movement, and, in justified cases, are equipped with skew limiters, which should operate automatically when an unacceptable skew value occurs.

There is a wide variety of designs of skew limiters. One of the most common are the so-called skew rod limiters, triggered by tensile-compression deformations of a special rod 1 mounted on a rigid crane support (Fig. 1.43).

Rice. 1.43. Installation of a swash rod on a rigid support

When the support runs out, its stand and rod 1 fixed on the support are deformed. To ensure the stability of the rod along its entire length, limiters 2 are installed. The deformation of the rod is transmitted to the hinged lever 3 of a special profile, which acts on the limit switches 4, which turn off the motors of the “run-out” support, turning them on only after the position of the supports is aligned. A light alarm is installed on the crane control panel to warn the driver about the presence of skew.

Specialists of the Staro-Kramatorsk Machine-Building Plant proposed a skew limiter mounted on a flexible support. In the limiter of this design, the deformation of the support is transmitted to the flexible rope 1 (Fig. 1.44), fixed on the span of the crane through the spring 2 and passing through the guide rollers 3 on the lower part of the flexible supports.

When running out, one leg of the support is subject to tension, the other to compression. Deformations of the racks cause the rope to move along the rollers. Rails 4 are fixed on the rope, which are engaged with a block of two wheels 5. A wheel of a larger diameter of the wheel block is engaged with rails 6 fixed on a rod 7. The movement of the rope 1 when the support runs out through the rails 4, the block of wheels 5 and rails 6 is transmitted rod 7, which with its protrusions acts on the limit switches 8, 9, 10, 11, which turn on the light and sound alarms, turn off the engine drive of the run-out support when a skew occurs, and also start the engine after the supports are aligned.

There are skew limiters that are triggered by torsion deformations of supports in the event of skew forces (Fig. 1.45).

Rice. 1.44. Warp limiter designed by B. V. Beglov and A. Ya. Ziskin

Rice. 1.45. Warp limiter, triggered by torsion deformations of a rigid support

An angular rod 2 is installed on the support 1, which, in the event of a misalignment, receives rotation along with the support. When turning the bar with its horizontal part, it acts on the limit switch 3, which is included in the motor circuit of the movement mechanism of the "run out" support. When the support runs out, the motor of the movement mechanism is turned off, when the supports are leveled, it turns on again.

In recent years, swashplates with selsyn type sensors have been increasingly used on cranes and loaders. Structurally, it is done like this. A non-drive trolley is attached to each of the supports, from the running wheels of which the selsyns rotate through the multiplier. The magnitude of the signal generated by the selsyns depends on the path traveled by the trolleys when moving the crane or loader. The selsyns are connected to a bridge circuit and, with uniform movement of both supports, the diagonals of the measuring bridge are balanced. When one of the supports runs out, the balance of the bridge is disturbed and the generated signal, which is fed into the electrical control circuit of the engine for moving the support, turns it off.

In the course of work the load-lifting equipment carries out many actions at the same time. At the same time, synchronicity is important. This is the most important factor in the smooth functioning of the machine. Special devices help control the workflow and ensure the safety of the operator and employees present on the site, the safety of other mechanisms and property: sensors, stops, etc.

The main purpose of safety devices for lifting equipment is to collect, process and record information about the position of the device, loading, preventing uncontrolled movement, impact. According to the requirements, each of the types of mechanisms must have appropriate devices, depending on design features and location. The purpose of the sensors is to fix the slightest malfunctions, send an alarm signal, which causes a complete stop for diagnostics and troubleshooting.

Types of crane safety devices

The operation of industrial and any other lifting equipment can pose a threat to employees performing their duties in the same area. For this reason, all devices are equipped with crane safety devices. The list is as follows:

limiter - automatically turns off the drive of the device if the maximum load capacity of the equipment is exceeded;
limit switch - a fuse that will allow you to turn off the drive in automatic mode when moving parts move outside the working area;
boom departure limiter - installed on jib cranes to turn off the mechanism when the minimum or maximum indicator is reached;
brake system (installed on actuators) - the main purpose is to reduce the speed of rotation of devices, a complete stop in order to fix the load in a certain position;
rotation limiter - prevents rotation of the rotary part in order to prevent breakage of electrical wires;
load capacity indicator - allows you to prevent overloading of crane equipment;
anemometer - determines the wind speed at which the operation of the device may be dangerous;
anti-theft device - prevents tower and gantry cranes from derailing under the influence of strong wind;
additional supports - ensure the stability of the equipment;
dead ends - are installed along the edges of the rails, beams in order to prevent the crane from coming off;
buffer devices - soften the possible impact of the stops against each other (rubber pillows, wooden blocks, hydraulic-type mechanisms are most often used).

This is far from full list instruments and sensors designed to ensure the safe operation of lifting equipment.

In addition, all easily accessible parts of the crane must be fenced. For this, lightweight metal structures are used, which can be removed for carrying out Maintenance, performance checks, settings, diagnostics and other activities provided for by security rules.

Lighting and signaling

All types of lifting equipment must be equipped with lighting devices for working in the dark and at night. The reason for this is also operation in poor visibility (for example, in fog). Installation of a tower crane involves the installation of fixtures that fully illuminate working area devices. In this case, the inclusion must be carried out by an independent electrical device, which must be placed on the portal. The working and equipment cabin, the machine room must also be illuminated. This applies to all types of cranes (tower, overhead, gantry, cantilever) and other types of lifting equipment. Lamps installed on the mechanisms themselves, even after the end of the working day, should remain on. In addition, lifting equipment must be equipped with an alarm. The sounds of the device must be well audible in the places of movement, lowering and lifting of the load, even in strong wind, rain and other adverse weather conditions.

Maintenance features

When should a crane be serviced? Most often it is carried out during the verification and diagnostics of the lifting device itself. The installer adjusts the systems in accordance with the current rules and regulations. When undergoing maintenance, the following are carried out:

external inspection of devices in order to check the quality of the installation;
determination of the state and correctness of the connection of electrical wires;
cleaning from pollution;
adjustment of systems and mechanisms;
definition of integrity metal structures, electrical mechanism and other systems;
checking the integrity of the installed seals, serviceability, performance.

After the maintenance is completed, the installer makes an appropriate entry in the log.

Repair and diagnostics

In the event of failure of lifting equipment, a thorough inspection should be carried out to identify the causes of failure. Most often, some parts and components require replacement, for example, microcircuits, sensors and boards. Repair is quite difficult technological process, which a professional adjuster with the appropriate permission and qualification has the right to perform. If malfunctions are detected, the operation of lifting equipment should be suspended until the breakdown is eliminated. After the repair, the service technician adjusts the required parameters. The frequency of inspection depends on the type of equipment, its carrying capacity, operating conditions and other important factors.