JPS6039235Y2 - Ready-mixed concrete additive dosing control device - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a device for controlling the amount of additives introduced into a mixer drum in order to maintain the quality of fresh concrete in a truck mixer.

The fresh concrete placed in the mixer drum undergoes a hydration reaction over time during transport, gradually losing its fluidity, which leads to a decline in workability during concrete pouring. The liquidity of 'J
It is measured as a slump value as specified in ISAIIO1.

) In recent years, in order to prevent a decrease in the slump value of fresh concrete being transported by a truck mixer, additives have been developed that can be added to and mixed with fresh concrete to freely adjust the slump value.

By adding this additive in small quantities to fresh concrete being stirred by a mixer drum, it is possible to prevent a decrease in slump value by using only a small amount of water that does not adversely affect strength. In addition to being able to obtain ready-mixed concrete with high quality and good workability, it has also become possible to transport high-strength ready-mixed concrete over long distances, which was previously considered impossible.

However, in order to obtain fresh concrete with a predetermined slump value, the amount and interval of addition of additives must be well adjusted.

It is difficult to decide in advance the amount of additive to add each time and the interval between additions because the reaction time varies depending on the quality of fresh concrete, temperature, mix, and other conditions.

Focusing on this problem, when the ready-mixed concrete in the mixer drum drops below the set slump value, a predetermined amount of additive is automatically added to keep the slump value of the ready-mixed concrete constant over a long period of time. A device for controlling the injection of additives that can be transported has already been proposed (Japanese patent application 1972-
No. 77938 (Special Publication No. 51-12045)).

This is used in hydraulically driven truck mixers to detect the operating pressure in the mixer drum's hydraulic motor, which is proportional to the slump value of fresh concrete, and convert it into a current value. Based on this current value (that is, the slump value), additives are It controls input.

By the way, in this type of truck mixer, the hydraulic pump, which is connected to the hydraulic motor in a closed circuit, is directly driven by the car engine, so the amount of hydraulic fluid discharged by the hydraulic pump increases or decreases depending on the engine rotation speed. As a result, the rotation speed of the mixer drum changes.

For example, as the mixer drum rotates faster, the viscosity of the fresh concrete in the mixer drum and the stirring energy increase.
The load increases due to the viscosity of the hydraulic oil in the closed circuit, and even if the slump value of the fresh concrete is the same, the operating pressure increases.

Therefore, in a truck mixer that does not have a control device that keeps the mixer drum rotational speed at a constant optimum level regardless of the rotational speed of the vehicle engine, the actual slump of ready-mixed concrete is increased by the increase in oil pressure due to the increase in mixer drum rotational speed. There is a problem in that the slump value is detected to be higher than the slump value, and as a result, the additives cannot be properly added, and ready-mixed concrete with the desired slump value cannot be obtained.

Therefore, the object of this invention is to solve the above-mentioned problems by detecting the rotational speed of the mixer drum and correcting the detected operating oil pressure of the hydraulic motor based on this detected value, that is, the load fluctuation.

Embodiments of this invention will be described below with reference to the drawings.

FIG. 1 is a schematic cross-sectional view of a track mixer.

1 is a mixer drum, 2 is a hydraulic motor, and a closed circuit 3 is formed between the hydraulic motor 2 and a hydraulic pump (not shown).

Reference numeral 4 denotes a hydraulic pressure detector that detects the inlet pressure of hydraulic oil in the hydraulic motor 2 as an electrical signal.

5 is means for detecting the rotation speed of the mixer drum 1;
This rotation speed detector 5 has a rubber roller 5b attached to the shaft of a tachogenerator 5a, and is freely rotatably supported by a bracket 5c fixed to the mixer frame 6. Being pressed against me.

The tachogenerator 5a generates a voltage corresponding to the rotational speed of the mixer drum 1 transmitted via the rubber roller 5b.

Each output of the oil pressure detector 4 and the rotational speed detector 5 is input to a controller 7, which will be described later, provided in the driver's cab.

Based on these electrical signals, the controller 7 outputs a drive signal to the device 8 for introducing the additive into the mixer drum 1 so that the slump value of the fresh concrete is maintained at the set value.

The circuit configuration of this controller 7 will be explained with reference to the block diagram shown in FIG.

20 is a subtraction circuit, and from the output voltage of the oil pressure detector 4,
The output voltage of the rotational speed detector 5 input through the amplifier 21 is subtracted, and the voltage difference is outputted to the low-pass filter 23 through the amplifier 22.

The low-pass filter 23 removes the high frequency components of this input signal, adjusts the pulse waveform, and outputs it to the monitor meter 24 to display the slump value of the fresh concrete, while the first to third comparators 25 to 27 provided in parallel Output to each.

A comparison voltage from the slump setting circuit 34 is input to the comparators 25 to 27.

However, depending on the internal resistance values of comparators 25 to 27,
The comparison voltage values are different values, and in this embodiment, the comparison voltage value of the first comparator 25 is the maximum, and is set so that it gradually decreases to the second and third.

Comparators 25-27 compare the output voltage of the low-pass filter 23 with a set voltage, and when the output voltage is greater, output high-level signals to AND circuits 28-30, which will be described later.

AND circuits 28 to 30 open their gates when the outputs of comparators 25 to 27 switch to high level, and oscillation circuit 31
And the output signal from the frequency dividing circuit 32 is sent to the drive circuit 33 of the additive injection device 8.

The frequency of the output signal of the oscillation circuit 31 determines the additive injection interval, and at the same time, the frequency of this output signal is changed to 172.1/4 by the frequency dividing circuit 32 and sent to each of the AND circuits 28 to 30. is input.

That is, when the output voltage of the subtraction circuit 20 is larger than the comparison voltage values of all the comparators 25 to 27, the gates of the AND circuits 28 to 30 are all opened via the comparators 25 to 27, and the drive circuit 33 is connected to the oscillation circuit 31 and A pulse signal from the frequency dividing circuit 32 is input.

In this case, since all the pulse signals are synchronized with each other, the drive circuit 33 operates the additive dosing device 8 with the output pulse corresponding to the pulse signal of the oscillation circuit 31, thereby making the additive dosing interval close, that is, This quickly reduces the slump value of fresh concrete.

If the output voltage of the subtraction circuit 20 decreases and, for example, the comparators 26 and 27 remain unchanged, but the output of the comparator 25 switches to the low level, the AND circuit 28 closes the gate.

Therefore, a pulse signal obtained by dividing the output of the oscillation circuit 31 by two is supplied to the drive circuit 33, and in the same manner, if the output voltage of the subtraction circuit 20 further decreases, the AND circuit 2
9 also closes the gate, and a pulse signal whose frequency is divided by four is supplied, and the amount of additive added decreases in accordance with the decrease in the slump value.

Therefore, it is possible to always supply additives in response to changes in the slump value of fresh concrete.

Note that the amount of additive added at one time can be adjusted by providing a variable resistor in the oscillation circuit 31, changing the resistance value, and expanding/reducing the pulse width of the output signal of the oscillation circuit 31.

By the way, when the slump value of fresh concrete is constant,
When the drum rotation speed changes, the hydraulic motor operating pressure changes accordingly, but the relationship between them is a nearly constant proportional relationship, especially when the drum rotation speed during stirring is 1 to 5R0P,
In the range of M, it is linearly proportional (a straight line graph).

Therefore, the output voltage of the subtraction circuit 20, which is obtained by subtracting the output voltage of the rotational speed detector 5 from the output voltage of the oil pressure detector 4, is the value obtained by correcting the load fluctuation due to the rotational speed of the mixer drum 1 from the working pressure of the hydraulic motor 2. And mixer drum 1
Since the output voltage corresponds only to the actual slump value of the ready-mixed concrete, the slump value can always be detected accurately and the appropriate amount of additive can be added.

Note that the rotational speed detector 5 is not limited to the one in the above embodiment, but may be configured to detect the flow rate of the hydraulic oil in the closed circuit 3 and indirectly detect the rotational speed of the mixer drum 10. You can.

Further, in the above embodiment, the oil pressure detector 4 is provided only at the hydraulic oil inlet of the hydraulic motor 2, but in order to compensate for leakage and temperature rise of the hydraulic oil in the closed circuit 3, a small boost pump is usually installed. In order to eliminate errors caused by this boost pressure, an oil pressure detector 4 is also provided at the hydraulic oil outlet of the hydraulic motor 2, and the operating pressure of the hydraulic motor 2 is detected from the differential pressure between the two oil pressure detectors 4. By doing so, a more accurate slump value can be detected.

As explained above, this invention detects the rotational speed of the mixer drum and compensates for fluctuations in the operating pressure of the hydraulic motor due to changes in the rotational speed of the mixer drum, so the slump value of the ready-mixed concrete on the mixer drum can be adjusted without error. Since it can be detected accurately and the addition of additives can be controlled based on this, the quality of ready-mixed concrete can be controlled with high precision, and the workability of placing concrete can be improved.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, and FIG. 1 is a schematic sectional view of a track mixer, and FIG. 2 is a block diagram showing the circuit configuration of a controller. 1... Mixer drum, 2... Hydraulic motor, 4... Oil pressure detector, 5... Rotation speed detector, 7... Controller .

Claims (1)

[Scope of utility model registration request] A hydraulically driven truck mixer includes means for detecting the working pressure of a hydraulic motor, means for detecting the rotational speed of a mixer drum, means for correcting a slump value calculated from a detected oil pressure value in accordance with a detected speed value, and 1. A ready-mixed concrete additive dosing control device, comprising means for comparing a corrected slump value with a set value and increasing or decreasing the amount of the additive to be added in accordance with the result.