Diagnosis and elimination of simple faults of the

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Diagnosis and troubleshooting of simple faults of torque limiter

torque limiter is an important safety device on crane, but because it uses complex electronic components, many users are afraid of it, so once there is a slight fault, it will be shelved. In fact, most of the time, the torque limiter does not have too much failure, and it can be restored to normal use as long as it is slightly adjusted. Next, taking the Japanese MS-3 torque limiter as an example, starting from the principle, we will talk about the diagnosis and troubleshooting of simple faults of the torque limiter

1 working principle of torque limiter

torque limiter is a device to prevent the lifting torque or lifting capacity of crane from exceeding the maximum allowable load under the current state of machinery. Its working principle is: according to the mechanical state parameters set before work and the mechanical state parameters detected during work, retrieve the maximum allowable load under the current state of the machine pre stored in the memory, and take this as the standard to compare the detected actual load with it, so as to determine whether the working state of the machine is safe. From the working process of the crane, the main parameters affecting its working condition are as follows:

· boom length L, which should be preset for fixed boom machinery such as crawler cranes, and detected by boom length sensor for telescopic boom cranes

· reduce the jib angle by lifting the accumulation of gas and coal dust θ, Detected by the angle sensor

· working radius R

· working area only affects cranes with different lifting curves in 360 ° different areas, such as most truck cranes

· hoisting wire rope magnification, preset

· lifting torque, detected by sensor

· lifting capacity, detected by transmitter

the voltage signal detected by the sensor is amplified at multiple levels and then converted into a/D signal, which is provided to the CPU. The CPU completes the retrieval, comparison and display of data, and sends an alarm when the lifting load is overloaded, and sends a stop command to the actuator at the same time. Figure 1 shows the schematic diagram of MS-3 torque limiter

2 fault diagnosis and troubleshooting

generally speaking, the faults of torque limiter are no more than five parts: sensor, gain circuit, central processing and storage, display and actuator. Generally speaking, the failure probability of the central processing, storage and display parts is small, and once there is a failure, you can only ask the manufacturer for help. In addition, other parts can be repaired

2.1 sensor

potentiometer is generally used for angle detection, arm length detection and azimuth detection. Its common fault phenomenon is that the displayed value on the display jumps, remains unchanged or changes randomly. Since these three sensors are only a simple mechanical device, and the maintenance is simple, the fault diagnosis usually starts from here. The inspection method is to use a multimeter to detect whether the output signal of the sensor is continuous, or remove the sensor, rotate it at a uniform speed by hand, and check whether the resistance change at the output end and the total resistance are consistent with the calibration value through the multimeter. If there is any difference, the specific phenomenon is common, indicating that the sensor has a problem, and replace it. These three sensors can be replaced by domestic products of the same specification, but the installation position of angle detector and azimuth detector is very important. Appropriate marks should be made during disassembly and installation should be done carefully

torque detection or weight detection sensors are generally electric bridges composed of strain gauges. There is a very simple method to judge whether a crane is equipped with a torque detection sensor or a weight detection sensor, that is, to see whether it is required to input the lifting wire rope magnification when setting the torque limiter. If necessary, it is a weight detection sensor, and vice versa. The common weight detection sensor is three roller type, and some crawler cranes install it on the gantry pulley. The most common torque detection sensor is installed at the connecting pin of the luffing hydraulic cylinder. Generally speaking, if these two kinds of sensors are broken, they cannot be repaired if the export amount in the first half of this year is not optimistic. We can only find the original manufacturer or professional manufacturer to solve the problem. Because these two kinds of sensors are electric bridges, the potential level is low and very sensitive, so shielded wires are often used, and once the shielding layer or joint is damaged, it often has a great impact on the test results. Therefore, when replacing the cable, we must use a whole intact shielded wire, and the solder joint is required to be smooth and reliable, and the joint should also pay attention to waterproof

2.2 amplification circuit

amplification circuit is an analog circuit on the main board, which is mainly used to gain torque or weight signals with low potential level. Common faults also show abnormal or no display. After eliminating the possibility of sensor faults, you can check this part. At present, most of the commonly used torque limiter amplification circuits use integrated circuits, so the substitution method can be used to check

there are two adjustment points in the amplification circuit, one is zero adjust and the other is span adjust. Some torque limiters (such as aml-m1 torque limiter commonly used on tadano crane) even directly lead out these two adjustment points and make them into knobs for adjustment. When the display is inaccurate, these two knobs can be adjusted. But before the adjustment, we should find out which one should be adjusted. Take the lifting weight as an example, use a group of weights with known weight as weights, lift them one by one, record the displayed value, and compare the difference between the displayed value and the real value. If the difference of each group remains unchanged, it should be adjusted to zero. If the difference of each group increases with the increase of lifting weight, the magnification should be adjusted

2.3 actuator

actuator is usually solenoid valve. The fault phenomenon is that everything is normal and the torque limiter also alarms, but the operation that should stop automatically can still be operated. At this time, you can check whether the corresponding solenoid valve coil is normal and whether there is an electrical signal to the solenoid valve when the crane is in the state that it should stop, so as to judge whether the fault is the solenoid valve or the outlet

2.4 maintenance example

a Ishikawa ihi500cch crawler crane used by our company, its boom base joint was damaged. When testing the new boom, the torque limiter showed that everything was normal, but during the full load test, it was found that when the lifted weight was actually overloaded according to the lifting curve table, but the torque limiter showed that it was still within the safe range, and the larger the angle, the more obvious this phenomenon. After verification, the weight of the lifted weight is consistent with the display, and the crane adopts a weight detection sensor, which is installed on the gantry. The arm length of 36m is preset, and there is no problem. Therefore, it is suspected that the position of the angle sensor is offset during installation. However, the base section of the crane boom is a truss structure, so it is difficult to find an accurate horizontal datum point. Therefore, the working radius of the boom at different angles (displayed values) was actually measured with a tape measure, as shown in Table 1

it can be seen from table 1 that there is a deviation between the displayed value and the measured value. According to the formula Δθ=θ Display - θ Measured = arccos (r display/l) - arccos (r measured/L) calculate the difference under each angle and take the average value. It is concluded that the display angle is about 3 ° larger than the measured angle. Since the machine has no angle zero adjustment knob, the fault disappears after turning the sensor counterclockwise about 3 ° around the hinge point of the pendulum

torque limiter is actually a simple example of the application of single chip microcomputer in industry. Its circuit is not too complex. As long as it has a certain foundation of Applied Electronic Technology and understands its basic principle, it is not difficult to repair. In the whole torque limiter, the data stored in ROM is actually the most valuable. Therefore, when repairing the motherboard, we must standardize the operation to prevent the data stored in ROM from being damaged. (end)

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