JPS6037410B2 - How to detect load on hoisting machine in crane etc. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting the load of a hoisted load when a crane or the like performs hoisting work on a hoisted rock.

Conventional methods for detecting the load on a hoisting rock using this type of crane include a load cell method in which a load cell is installed on the hoisting rock on a club trolley to display the load, and a current transformer (CT) is installed on the input side of the hoisting motor. A power-based load display method has been proposed in which the output current of the current transformer is applied to an indicator meter via a power converter, and the load is displayed according to changes in the input current.

However, in the former case, the mechanical structure is complicated because the load cell is attached to the bottom of the hoisting rock, and wiring from the crane body is required, making the whole thing expensive.
Furthermore, in the latter case, mechanical considerations are not required compared to the load cell method, but a potential transformer (PT) and two current transformers (CT) are required.

Furthermore, in the case of light loads, detection errors increase due to the no-load current of the hoisting motor, limiting the load detection range, which limits the range of use for crane cargo handling where the suspended load is not constant. There are other difficulties.

The present invention detects the load by capturing the secondary current characteristics of the motor. It can be detected with only one CT, has fewer components and fewer wirings, and can display the load over a wide range. We aim to ensure that this is carried out throughout the period.

The present invention will be explained below based on examples.

That is, the present invention extracts a value proportional to the secondary current of the hoisting motor with a current detector 1, squares that value with a square integration circuit 2, and calculates a predetermined cycle of the current of the generation cycle on the secondary side. The number of pulses generated by the constant pulse generation circuit 3 during the cycle is compared, and the number of pulses generated by the constant pulse generation circuit 3 is compared.
Then, by measuring the number of pulses during the cycle, a signal that is a constant of the motor slip is generated, and after integrating the output value of the F/V converter 5 and the square value of the current using the integrating circuit 6. The gist is that the voltage adjustment circuit 7 converts the tare value of the hoisted rock into a signal proportional to the subtracted hanging load, and the suspended load is displayed on the display 8.

FIG. 1 is an electric circuit diagram (equivalent circuit of a three-phase wire-wound motor) for explaining the principle of a method for detecting a load on a hoisted rock in a crane or the like according to the present invention.

In the figure, the secondary circuit C2 of the motor is shown as a series loop consisting of a resistor r2/S and an actance x2 generated by the above-mentioned coil.

In the figure, S indicates slippage. Now, assuming that the generation circuit of the motor secondary circuit is 12 and the secondary voltage is E2, the secondary input, that is, the synchronous wattage P2 is expressed by the following equation.

P2 = 31 times W) ------'1} That is, motor torque T is proportional to P2. T=KP2 where K is a constant.

In addition, in equation (1), resistance r2 may be changed at the time of starting when secondary resistance control is performed, but it remains constant during operation, so motor torque T is the sum of the square value of current value 12 and slip S. Therefore, the change in load according to motor torque can be accurately determined by measuring the square value of the current value 12 and the slip S.

The present invention has been made based on the above principle, and its gist will be further explained based on FIG. 2.

What is shown in FIG. 2 is a block diagram illustrating the load detection method of the present invention. A current value i proportional to the secondary current 12 of the hoisting motor IM is now taken out by a current detector 1 having a current transformer or the like, and the value of this current value i is set as i2 by a square integration circuit 2. At the same time, the detection circuit a is applied to the slip measurement circuit b.

This measurement circuit b consists of a constant pulse generation circuit 3 and a gate circuit 4.
It is mainly composed of a frequency-to-voltage converter (F/V converter) 5. Originally, the slip S is s when the synchronous rotation speed with respect to the frequency is Ns and the actual rotation speed of the motor is NR.
The cycle f generated in the detection circuit a is proportional to the motor rotation speed NR.

That is, the S ratio becomes f, and as the load increases, f decreases.
That is, since the time for one cycle (or 1/2 cycle) is long, the above-mentioned constant pulse generation circuit 3 is used to measure this time. In other words, the length of the cycle, i.e., the slippage, is numerically displayed based on the number of pulses included in the cycle f, and the detection circuit a and the constant pulse generation circuit 3 are applied to the gate circuit 4 in parallel. ,
The circuit 4 generates the number of pulses in one cycle.

Figure 3 shows the gist of this process, and to simplify the explanation, it shows an example of generating the number of pulses during a half cycle. The number N of pulses P applied from 3 is measured by the gate circuit 4, and the number of pulses is applied to the F/V converter 5 as a number of pulses with a constant amplitude, and the converter 5 converts it into a DC voltage. Then, the slip is extracted as a voltage based on the difference with the DC voltage that should be obtained at the number of cycles corresponding to the synchronous rotational speed NS, and is applied to the integration circuit 6 as the reciprocal 1/S.

Then, the integrating circuit 6 outputs a signal electromagnetic signal of the product of the squared current value i2, that is, i2×. Next, the signal voltage here is subtracted by the tare value of the onboard machine, and is applied to the voltage adjustment circuit 7 in order to match the suspended load value.

The load value W which is proportional to the hanging load value after adjusting the tare value to 0 by this voltage adjustment circuit is displayed on the load display 8. Therefore, according to the present invention, a decrease in the rotational speed of the motor (reduction in the number of cycles) and a change in the secondary/side current value and slip are detected as the load changes, and the load is detected based on this. This solves the drawbacks of the conventional load cell method being complicated and expensive, or the complexity of the detector in the method of measuring input current and voltage changes of motors.
It also has the advantage of being able to perform accurate measurements over a wide range of conditions, from light loads to heavy loads, and having a simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram for explaining the principle of the method of the present invention, FIG. 2 is a block diagram, and FIG. 3 is a diagram for explaining the cycle-pulse relationship in a gate circuit. 1... Current detector, 2... Square multiplying circuit, 3... Constant pulse generation circuit, 4...
・Gate circuit, 5...F/V converter, 6...
・Integrator circuit, 7... Voltage adjustment circuit, 8...
Load indicator, IM...Hoisting motor, 12...
...Secondary current of the hoisting motor, i...Current value,
W...Load value. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. A value proportional to the secondary current of the hoisting motor of a hoisting machine in a crane, etc. is taken out by a current detector, that value is squared by a square integration circuit, and the pulse of the secondary current is calculated by a predetermined cycle. The slip of the motor is measured by comparing the number of pulses generated from a constant pulse generation circuit and the number of pulses during the cycle, and after integrating the square value of the current and the time of one cycle, the voltage is applied to the voltage regulation circuit. A method for detecting a load on a hoisting machine in a crane or the like, characterized in that the tare value of the hoisting machine is subtracted from the hoisting machine, and the suspended load is measured or displayed by subtracting the tare value of the hoisting machine and converting it into a signal proportional to the suspended load.