SU368175A1 - LOAD LIMITER - Google Patents

Description

one

The invention relates to the field of lifting and transport machinery, in particular, to limiters of lifting capacity.

Load capacity limiters are known, which contain a mechanical tension sensor in the load edge, a contact system connected to the sensor, and an elevator motor control circuit relay. An element is also provided in these limiters to ensure the transmission of dynamic overloads. Such an element prevents the operation of the limiter under the action of dynamic overloads accompanying the operation of the load lifting mechanism, especially in the initial period of cargo separation from the base.

In order to increase the accuracy of the operation, the dynamic overload element in the proposed limiter is implemented as a delay unit connected in series with the mechanical sensor contact set up to open when exceeded, the operating load limit, and the delay contacts of the relay ... are included in the lift motor control circuit the response time of the block is assumed to be equal to the duration of the open contact in the open state when the force changes cyclically in the lift m rope during lifting.

In addition, the described limiter can be made with an additional mechanical sensor contact, which deactivates the delay unit when peak loads occur. This ensures reliable protection of the crane against significant overloads.

FIG. I shows the scheme of installation of the limiter on the mechanism of lifting; in fig. 2 - principle electrical circuit of the limiter; in fig. 3 - schedule limiter.

The load limiter is mounted on the crane truck and contains a mechanical sensor / load, to the crank 2 of which a hoisting cable 3 is connected, supporting the hook suspension 4.

Sensor 1 is connected to normally closed contacts K1 and K2. Electrical circuit

the limiter is powered by direct current. The winding of the electromagnetic relay is connected to the mains through the contact / C / and its own interlocking contact. Parallel to relay P, in series with contacton K1, there is a delay chain formed by capacitance C, as well as fixed and adjustable resistors R and Rp. The second contact of the K2 sensor is included in this chain. Through the contacts of the relay P is also carried out

powering red lamp LK (alarm

overload), a green lamp LZ (normal operation) and power supply goes to the device / W of the engine starts of the load lifting mechanism in the lifting direction. The circuit also provides for the button / Sr when the contacts are closed, which supplies power to the device 0/7 of switching on the lifting motor to lowering and to the relay P to bring eiro to a state (restoration of the contact circuit /).

When lifting loads of the maximum weight (or close in weight to the limit) by a bridge-type crane, regardless of the position of the load carriage, the natural oscillation periods of the structure will have an approximately stable value. The tension in the hoisting rope will vary accordingly. The graphs of the force changes in the rope for the case of lifting loads, weighing Q and Q are given in FIG. 3, respectively, solid and dash-dotted lines. These loads correspond to the upper and lower limits, the limiter at which the values of dynamic overloads, typical for a normal operation of the crane, the greatest for a given crane, should allow its operation.

The value of Q is established for reasons of ensuring the durability of the crane. The value of Q is determined by the fact that the time ti at which the contacts / C / of the mechanical sensor, adjusted to the maximum allowable during operation Qb, slightly exceeding Ql, remain open, would be the same for both Q and Q.

Obviously, in the event that the value of the lifted load exceeds the value of Q, the upper limit of the stresses increases, and with it the duration of the period at which the dynamic load value exceeds ti also increases. Accordingly, the residence time of contact K.1 increases in an opened state.

When the load lifting mechanism is activated, power is simultaneously supplied to the limiter. Pressing the / C "button supplies power to the coil of the relay P, whose contacts are closed, as a result of which the LZ lamp and the LK lamp come on. goes out, and the latching contact provides power to the coil even after the / C "button is turned off. The NM lifting chain is also closed. A capacitor C of the delay chain is charged. When lifting a load, if the magnitude of the dynamic -load exceeds Q, the contact L / opens. However, the winding of the relay P receives power from the delay chain, and this provides the necessary delay in the operation of the relay P for time / 4er. In case the load exceeds Q, the opening time of contact K1 will exceed 4. and charging capacity C will be insufficient to hold the relay core P, the latter will open, as a result of which the / 7M circuit will open, the LZ lamp will go out and the overload lamp will light up.

Contact K2 will continue to be closed. Correspondingly, its position of the circuit elements is shown graphically in FIG. 3 (diagram I).

To turn on the engine to lower, press the I button, which will close the OP circuit.

In the case of a rapid lifting of a very large weight load on the ropes will increase dramatically (the dash-dotted line in Fig. 3).

Here, contact K.1 is initially opened, however, the delay chain will still hold the relay P. After this, contact K2 is triggered, which is tuned to the limit

the peak load Qz, as a result of which the relay P will be de-energized. The lifting mechanism will immediately stop (diagram II in FIG. 3). Thus, protection against

overloads of loads that exceed the limit set by weight Q. At the same time, dynamic overloads that can occur during normal crane operation are passed through and speed is provided

limiter when lifting loads that are significantly higher than the weight permissible and l l under the action of peak loads.

Subject invention

Claims (2)

1. A load limiter mainly for bridge-type edges, comprising a mechanical force sensor in a hoisting rope, a contact system associated with the sensor, a dynamic overload admission element and a lifting mechanism motor control relay, characterized in that, in order to increase the accuracy of the limiter, the element Dynamic overloads pass is made in the form of a delay unit connected in series with the set to open when the maximum operating load is exceeded and the mechanical contact sensor, wherein the block lag relay contacts are included in a lifting motor control circuit, and the response time of the block is received equal to the length of residence in the open state of said contact force changing in cyclic in the lifting rope in the process of lifting. 2. The load limiter of claim 1, characterized in that, in order to ensure reliable protection of the crane against overloads, it made with an additional contact of the mechanical sensor, disconnecting the delay unit when peak loads occur. ff p to LJUHL on pm R  R fa-i-- -4 bP v | o o-1