JPH07245987A - Load monitoring apparatus - Google Patents

Abstract

PURPOSE:To make it possible to monitor load with a motor power corresponding to the load of operation itself, by determining a motor power value based on a value obtained by subtracting a motor power during idle running from that during duty operation. CONSTITUTION:A motor power during idle operation is determined by means of a power calculating means 21, and is stored in a storage unit 12. The motor power is read from the storage unit 12, and is subtracted from a motor power during duty operation determined by means of the power calculating means 21. A comparing means 26 compares the resultant value of power with a proper motor power range read from the storage unit 12, and judges whether the result of the subtraction is within the proper range. If the subtraction result is out of the range, a trouble signal is output to an output unit 15, and a motor control unit 2 interrupts the power supply to a motor M.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for monitoring loads on various machines such as machine tools in which an electric motor is used as a drive source.

[0002]

2. Description of the Related Art A motor is used as a drive source,
For example, in a machine tool, when an abnormal load condition occurs,
Continuing to drive the motor as it is will result in burnout of the motor, damage to the tools, and a significant reduction in efficiency. Therefore, monitoring the load during work is an essential monitoring task. It is one of the items. Therefore, conventionally, the power supply value to the motor (referred to as motor power value) is detected, the load is calculated, the motor power is adjusted so that the load is within an appropriate range, and the power supply to the motor is cut off. There is.

[0003]

However, in the prior art, the load is monitored by obtaining the motor power while the machine tool is working, that is, during load operation. Although there is no problem in the above, in recent years, not only the overload monitoring but also the load (actual load) fluctuation of the work itself performed by the machine tool, the motor torque value monitoring, and the torque fluctuation through the display Although there are strong demands for various functions such as observation by magnifying observation, there was a problem that it was not possible to cope with these.

The present invention has been made in view of the above circumstances, and an object thereof is to subtract the motor power value during idle operation from the motor power value during load operation to realize the actual work corresponding to the work itself. It is an object of the present invention to provide a load monitoring device capable of monitoring the load and the actual torque and also capable of enlarging and displaying the electric power value and the torque value as necessary by changing the display scale.

[0005]

A load monitoring device according to a first aspect of the present invention includes a motor as a power source, and a motor power value during load operation in a load monitored machine in which idle operation and load operation are performed. In the device for monitoring the motor load by determining whether or not the motor power value is within a predetermined appropriate power range, the motor power value during idle operation and the appropriate motor power range during load operation are stored. And a storage unit for obtaining a motor power value during load operation,
Means for subtracting the motor power value during idle operation stored in the storage unit from the motor power value during load operation obtained by the means, and the subtracted power value obtained by the means are stored in the storage unit. And comparing means for comparing whether or not the power is within the appropriate power range, and outputting an abnormal signal when the power is out of the appropriate power range.

A load monitoring apparatus according to a second aspect of the present invention includes a motor as a power source, a load is connected to the motor via a power transmission mechanism, and the load monitoring target machine performs idle operation and load operation. In the device for monitoring the load by determining the torque value from the motor power value during the load operation in step 1, and determining whether the torque value is appropriate,
A storage unit that stores a motor power value during idle operation and an appropriate torque range during load operation, power calculation means that determines the motor power value during load operation, and motor power value during load operation that is calculated by the power calculation means Means for obtaining a subtracted power value obtained by subtracting the motor power value during idle operation stored in the storage section, means for detecting the frequency of the motor power source during load operation, or the rotation speed of the output shaft of the power transmission mechanism. And a means for obtaining a torque value during load operation based on the obtained motor power supply frequency or the rotational speed of the output shaft, the subtracted power value, and the motor specifications stored in the storage section. It is characterized by further comprising: comparing means for comparing the obtained torque value with an appropriate torque range stored in the storage unit, and for outputting an abnormal signal when the value is out of the appropriate torque range.

A load monitoring apparatus according to a third aspect of the present invention includes a motor as a power source, a load is connected to the motor via a power transmission mechanism, and the load monitoring target is subjected to idle operation and load operation. In a device for obtaining a torque value from a motor power value during the load operation of a machine, determining whether or not the torque value is appropriate, and monitoring the load, the motor specifications, the motor power value during the idle operation, the display unit Storage unit for storing the display scale data and the appropriate torque range, power calculation means for obtaining the motor power value during the load operation, and the storage unit for storing the motor power value during the load operation obtained by the power calculation means. Means for subtracting the electric power value of the motor during idle operation to obtain the subtracted electric power value, and means for detecting the motor power supply frequency during load operation or the output of the power transmission mechanism And a means for determining the torque value during load operation based on the obtained motor power supply frequency, or the rotation speed of the output shaft, the subtracted power value, and the motor specifications stored in the storage unit. Scaling means for displaying the torque value on the display unit based on the torque value obtained by the means and the display scale data stored in the storage unit; and the torque value stored in the storage unit. It is characterized by further comprising: comparing means for comparing with the proper torque range and outputting an abnormal signal when the torque is out of the proper torque range.

[0008]

According to the first aspect of the present invention, whether or not the value obtained by canceling the no-load loss during idle operation by subtracting the motor power value during idle operation from the motor power value during load operation is within the proper motor power range. In addition to being able to judge the actual load of the work itself, it is also possible to quickly take measures such as cutoff of power supply to the motor by the abnormal signal output when it is outside the proper motor power range. Becomes

According to the second aspect of the invention, the motor torque value is obtained based on the value obtained by canceling the no-load loss during idle operation, the motor specification and the motor power supply frequency, or the rotation speed of the output shaft of the power transmission mechanism. This makes it possible to monitor the load with the actual torque value corresponding to the work itself.

In the third aspect of the invention, similarly, the torque value is obtained based on the value obtained by canceling the no-load loss during idle operation, and the scaling calculation means displays the torque value on the display unit based on the torque value and the display scale data. By changing the scale, the transition of the torque value can be visually recognized more finely.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. (Embodiment 1) FIG. 1 is a block diagram showing the configuration of a load monitoring apparatus according to the present invention, in which M is a motor, 1 is a power supply, and 2 is a power supply.
Is a motor controller, 3 is a power supply line for the motor M, and 6 is a load monitoring device according to the present invention.

The power supplied from the power source 1 is adjusted by the motor control unit 2 and supplied to the motor M. For example, a tool of a machine tool is connected to the motor M via a power transmission mechanism (not shown), and a load is applied to the tool. The motor control unit 2 adjusts the power supply to the motor M, and also controls the power supply to the electric motor M based on a command from the load monitoring device 6. The load monitoring device 6 includes a CPU 11, a storage unit 12, a display unit 13, a key / terminal input unit 14, and an output unit 15.

The storage unit 12 has a CPU 11 through a keyboard connected to the key / terminal input unit 14 by an operator.
Is operated to write the upper limit value and the lower limit value that define the proper motor power range, and when the motor M and the machine tool are idle, the power calculation means of the CPU 11 is operated by the timing signal from the key / terminal input unit 14. The electric power value of the motor at the time of idle operation output from 21 is written. The upper and lower limits that specify the proper motor power range are the upper and lower limits of the load corresponding to the work itself performed by the machine tool, that is, the actual load, even if the machine tool is continuously operated. It is determined experimentally and empirically as a value that does not cause burnout and tool damage, and that can obtain sufficient work efficiency.

The CPU 11 includes a power calculation means 21, a no-load loss canceling means 22 during idle operation, and a comparing means 26.
It has the function as. In the electric power calculation means 21, the motor M is in the idle operation state (the tool of the machine tool is idling) based on the data obtained from the motor control unit 2 through the power supply line 3 to the motor M and the key / terminal input unit 14. In that case, the motor power value is calculated, and when the motor M is working with a machine tool, the motor power value is calculated. The timing signal from 14 is stored in the storage unit 12, and the motor power value during load operation is given to the no-load loss cancel calculation unit 22 during idle operation. As the motor power value during idle operation, a value that has been empirically obtained in advance may be stored in the storage unit 12.

The no-load loss canceling calculation means 22 during idle operation subtracts the motor power value during idle operation read from the storage unit 12 from the motor power value during load operation given from the power calculation means 21 and subtracts it. The power value is given to the comparison means 26 and displayed on the display unit 13.

The display unit 13 displays the value obtained by canceling the no-load loss during idling as shown in FIG. 2 (a), for example. FIG. 2A shows a display mode on the display unit 13 of the first embodiment, and FIG. 2B shows a display mode on the display unit 13 when the no-load loss cancellation calculation means 22 at the time of idling is not provided. 4A and 4B are explanatory diagrams respectively showing the time on the horizontal axis and the motor power value (%) when the rated power of the motor is 100% on the vertical axis.

As is clear from comparison between FIG. 2 (a) and FIG. 2 (b), in FIG. 2 (b), since the motor power value includes the load during idle operation, the load of the work itself is Although difficult to recognize, in FIG. 2A, the subtracted power value obtained by subtracting the motor power value during idle operation from the motor power value during load operation is displayed. As a result, the motor power value corresponding to the actual load is displayed. Thus, the actual load can be seen at a glance.

The comparing means 26 determines whether or not the subtracted power value given from the no-load loss canceling operation means 22 during the idle operation is between the upper limit value and the lower limit value defining the proper motor power range read from the storage section 12. That is, it is determined whether or not it is within the proper motor power range. If it is within the proper motor power range, no signal is output, but if it is outside the proper motor power range, an abnormal signal is output to the output unit 15.

When an abnormal signal is input, the output unit 15 outputs a control signal to the motor control unit 2 so that the motor control unit 2 cuts off power supply to the motor M.

FIG. 3 is a flow chart showing the processing steps in the first embodiment. First, the CPU 11 is set to the program mode according to an instruction input by the operator through the keyboard connected to the key / terminal input unit 14 (S
1), the upper limit value and the lower limit value that define the appropriate motor power range are stored in the storage unit 12, the motor M and the machine tool are idled, and the motor power value at that time is obtained by the power calculation means 21. Is stored in the storage unit 12 (S
2). Next, similarly, the CPU 11 is set to the monitoring mode according to the instruction input through the keyboard (S3).

In the load operating state, the electric power calculating means 21 obtains the motor electric power value, and the no-load loss canceling arithmetic operation means 22 during the idling operation subtracts the motor electric power value during the idling operation from this motor electric power value. Figure 2 shows the subtracted power value
The display unit 13 is displayed in the manner as shown in (a), and the comparison unit 26 monitors the comparison with the proper motor power range. If the range is outside the proper motor power range, an abnormal signal is output to the output unit 15. Then, the output unit 15 outputs a control signal to the motor control unit 2 to cut off the power supply to the motor M. In the first embodiment as described above, the motor electric power value corresponding to the actual load of the work can be obtained, which is extremely convenient for directly monitoring the actual load change.

(Embodiment 2) In this embodiment 2, a power supply power value (referred to as motor power) is obtained based on data obtained from the motor control unit 2 through the power supply line 3 to the motor M during load operation, and this motor power value is obtained. It is possible to subtract the motor power value at the time of idling from this, obtain a torque value (hereinafter referred to as the actual torque value) from this subtracted power value, and display this.

FIG. 4 is a block diagram showing the structure of the second embodiment. In the second embodiment, the upper limit value and the lower limit value for defining the proper torque range in the storage unit 12, the motor specifications including the number of motor poles, and the idle value are set. The motor power value and the like during operation are stored as in the case of the first embodiment. The proper torque range is the upper and lower limits of the actual torque value corresponding to the actual load of the work itself performed by the machine tool. C
The PU 11 has the functions of the frequency calculating means 23 and the torque calculating means 24 of the motor power source in addition to the functions of the power calculating means 21, the no-load loss canceling calculating means 22 at the time of idle operation, and the comparing means 26 shown in FIG. .

The motor power supply frequency detecting means 23 is a power supply line 3 from the motor control section 2 to the motor M 3, a key / terminal input section 1
4, the data is taken in, the frequency of the motor power supply is detected, and this is given to the torque calculation means 24. The torque calculation means 24 is located between the no-load loss cancellation calculation means 22 at the time of idling and the display unit 13 and the comparison means 26.
Based on the subtracted power value given from the no-load loss cancellation calculation means 22 at the time of idle operation, the motor power supply frequency given from the frequency detection means 23, and the motor specifications (the number of motor poles, etc.) read from the storage unit 12. , For example, the torque T is calculated according to the following equation (1), and the calculated torque T is displayed on the display unit 13
And to the comparison means 26. T = (974 × W) / N (1) where N = (120 × f) / P W: subtracted power value f: motor power supply frequency P: motor pole number N: motor rotation speed

The display unit 13 displays the motor torque value T corresponding to the actual load in time series. Further, the comparison means 26 compares the motor torque value T given from the torque calculation means 24 with the upper limit value and the lower limit value defining the proper torque range read from the storage section 12, and the motor torque value T is within the proper torque range. In the case where it is out of the proper torque range, an abnormal signal is output to the output unit 15. The output unit 15 outputs a control signal to the motor control unit 2 to cut off the power supply to the motor M. Note that the entire processing procedure is substantially the same as the flowchart shown in FIG.

FIG. 5 is a flow chart showing a torque value calculation process in the CPU 11 in the second embodiment. The motor power supply frequency is measured (S11), and the motor power supply frequency and the no-load loss cancel calculation means 22 at the time of idle operation are shown.
The rotation speed N of the motor is obtained from the subtracted power value given from the above and the number of motor poles which is the motor specification stored in the storage unit 12 (S12), and the motor torque value T is calculated from the equation (1).
Is calculated (S13). Other configurations and operations are substantially the same as the configurations of the first embodiment shown in FIG. 1, and corresponding parts are designated by the same reference numerals and description thereof is omitted.

In the second embodiment, the motor torque value is calculated based on the subtracted power value obtained by subtracting the motor power value during idle operation from the motor power value during load operation,
By displaying this on the display unit 13, it becomes possible to monitor the load with a torque value corresponding to the actual load.

(Third Embodiment) In the third embodiment, the motor torque value corresponding to the actual load is scale-converted and displayed on the display unit. FIG. 6 is a block diagram showing the configuration of the third embodiment. In the third embodiment, the storage unit 12 has a motor specification including the number of motor poles, an upper limit value and a lower limit value that define an appropriate torque range, and an idle operation. In addition to the motor power value at that time, scale conversion data is stored. The upper and lower limits of the appropriate torque range are the torque values corresponding to the actual load multiplied by the conversion rate of the scale conversion data. Further, the CPU 11 has a function as a scaling calculation means 25 in addition to the configuration of the second embodiment shown in FIG.

The scaling calculation means 25 is located between the torque calculation means 24 and the display section 13 and the comparison means 26, and converts the motor torque value given from the torque calculation means 24 and the scale conversion data read from the storage section 12. Based on this, the motor torque value is displayed on the display unit 13 in the manner as shown in FIG. FIG. 7A shows the display mode of the motor torque value displayed on the display unit 13 in the third embodiment, and FIG. 7B shows the scaling calculation means 2.
6 is an explanatory diagram showing a display mode of a motor torque value displayed on a display unit 13 when the display device 13 does not include 5; FIG.

In each of FIGS. 7A and 7B, the horizontal axis represents time and the vertical axis represents motor torque (%) (ratio when motor rated output is 100%). The graph of FIG. 7A shows a case where the upper limit side of 50% is enlarged to 100% and the lower limit side of 25% is enlarged to 0% as scale conversion data stored in the storage unit 12. There is.
As is clear from comparison between FIG. 7 (a) and FIG. 7 (b), the motor torque range of 25% to 50% shown in FIG. 7 (b) becomes 0% to 100% in FIG. 7 (a). The image is enlarged, in other words, enlarged four times in the vertical axis direction.

Next, the operation of the third embodiment will be described with reference to the flow chart shown in FIG. First, the load monitoring device 6
The program mode is set by the operator through the keyboard connected to the key / terminal input section 14 (S2).
1) Then, in addition to the motor specification, the upper limit value and the lower limit value that define the proper torque range through the keyboard, two values on the vertical axis to be expanded as scaling conversion data, for example, in the case of FIG. A motor torque value of 50% that expands to 100% is set to a program address, and a motor torque value of 25% that expands to 0% is set to another program address (S2
2) After that, it switches to the monitoring mode through the keyboard (S23). As a result, the motor torque value obtained by the torque calculating means 24 is given to the scaling calculating means 25, and the scaling calculating means 25 displays the motor on the display unit 13 in the manner shown in FIG. 7A based on the set scale conversion data. Display the torque value.

In the third embodiment, the torque calculation means 2
Although the motor torque value calculated in 4 is given to the comparison means 26 through the scaling calculation means 25, the motor torque value may be directly given to the comparison means 26 from the torque calculation means 24. Other configurations and operations are substantially the same as those of the second embodiment, and corresponding parts are denoted by the same reference numerals and the description thereof is omitted.

(Embodiment 4) It is inevitable that a slip of 3 to 5% usually occurs in the motor and the power transmission mechanism.
Conventionally, the motor torque value is calculated assuming that there is no such slip, and an error due to this is inevitable. In the fourth embodiment, the rotation speed sensor 5 is provided on the output shaft of the power transmission mechanism 4 for transmitting the motor output to the tool or the like in order to eliminate the error caused by the slip, and the output is obtained from the rotation speed sensor 5. The output shaft torque value is calculated by the torque calculation means 24 from the rotation speed and the output from the no-load loss cancellation calculation means 22 during idle operation.

FIG. 9 is a block diagram showing the configuration of the fourth embodiment. In the fourth embodiment, the storage section 12 stores motor data such as the number of motor poles and motor efficiency, machine tool data such as efficiency, and scale conversion data. The upper limit value, the lower limit value, and the motor power value during idle operation that define the proper output shaft torque range are stored. The CPU 11 is the CPU shown in FIG.
The rotation speed sensor 5 provided on the output shaft of the power transmission mechanism 4 in place of the function of the frequency detection means 23 of the motor power source 11
Speed detecting means 2 for detecting the rotation speed of the output shaft from the output of
It has substantially the same configuration as that having the function of 7. The rotation speed detection means 27 detects the rotation speed N of the output shaft of the power transmission mechanism 4 based on the output signal from the rotation speed sensor 5, and supplies this to the torque calculation means 24.

The torque calculation means 24 stores the rotation speed N, the motor power value corresponding to the actual load given from the no-load loss cancellation calculation means 22 during idle operation, and the storage section 12.
Based on the machine tool data such as the motor pole number, the motor data including the motor efficiency, and the efficiency read from the following, the output shaft torque value T (kgf.
m) is calculated, and this is given to the scaling calculation means 25. T = (974 × W _out ) / N (2) where W _out = W _IN × η W _out : Motor output W _IN : Motor input power η: Efficiency according to rotation speed and load factor Scaling calculation means 25 The output shaft torque value T is displayed on the display unit 13 based on the scale conversion data read from the storage unit 12, and the output shaft torque value T corresponding to the value obtained by multiplying the scale conversion rate is given to the comparison unit 26. The comparison means 26 determines whether the output shaft torque value T is within the proper output shaft torque range read from the storage unit 12, and if it is outside the proper output shaft torque range, outputs an abnormal signal to the output unit 15. The other structure is substantially the same as that of the third embodiment,
Corresponding parts are assigned the same numbers and explanations thereof are omitted.

Next, the operation of the fourth embodiment will be described with reference to the flow chart shown in FIG. FIG. 10 is a flowchart showing the processing steps in the monitoring mode in the fourth embodiment. During the load operation, the output signal from the rotation speed sensor 5 is taken in to obtain the rotation speed of the output shaft of the power transmission mechanism 4 by the rotation speed detecting means 27 (S31), while the motor power value is calculated by the power calculating means 21. Ask (S32). The no-load loss cancellation calculation means 22 during idle operation subtracts the motor power value during idle operation from the motor power value during load operation, and the torque calculation means 24 calculates the subtracted power value and the output shaft of the power transmission mechanism 4. The output shaft torque value T is obtained based on the rotation speed of the motor, the motor data, and the machine tool data (S33).
In step S34, it is determined whether the torque is within the proper output shaft torque range and the load is monitored through the torque value.

The other operation is substantially the same as that of the third embodiment, and the explanation is omitted. In the fourth embodiment as described above, the error caused by the slip of the power transmission mechanism on the way from the motor to the tool can be eliminated, and finer monitoring can be performed based on the actual torque value corresponding to the work load. Become.
The output of the torque calculating means 24 may be directly applied to the comparing means 26 without passing through the scaling calculating means 25. Further, the rotation speed sensor 5 and the rotation speed detecting means 27 shown in the fourth embodiment may be applied instead of the frequency detecting means 23 in the second embodiment.

[0038]

As described above, according to the first aspect of the present invention, it is determined whether the comparison means is within the proper motor power range based on the value obtained by subtracting the motor power value during idle operation from the motor power value during load operation. Therefore, the actual load corresponding to the work itself can be monitored. In the second aspect of the invention, the torque value of the motor is obtained based on the value obtained by subtracting the motor power value during idle operation from the motor power value during load operation, and the comparison means determines whether this is within the proper torque range. Since it is determined whether or not it is possible to obtain a motor torque value or an accurate output shaft torque value corresponding to the work itself, more precise monitoring is possible.

In the third invention, the output shaft torque value corresponding to the work itself can be displayed on the display unit based on the scale conversion data, and the transition of the torque value can be visually recognized in more detail.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing a display mode on a screen of a display unit.

FIG. 3 is an explanatory diagram showing a processing process in the first embodiment.

FIG. 4 is a block diagram showing a configuration of a second embodiment.

FIG. 5 is a flowchart showing a processing procedure in a monitoring mode according to the second embodiment.

FIG. 6 is a block diagram showing a configuration of a third embodiment.

FIG. 7 is a schematic diagram showing a display mode on a screen of a display unit.

FIG. 8 is a flowchart showing the processing steps of the third embodiment.

FIG. 9 is a block diagram showing a configuration of a fourth embodiment.

FIG. 10 is a flowchart showing a processing procedure in a monitoring mode according to the fourth embodiment.

[Explanation of symbols]

 1 power supply 2 motor control unit 3 power supply 4 power transmission mechanism 5 rotation speed sensor 6 load monitoring device 11 CPU 12 storage unit 13 display unit 14 key / terminal input unit 15 output unit 21 power calculation unit 22 no load loss during idle operation Cancel calculation means 23 Motor power frequency detection means 24 Torque calculation means 25 Scaling calculation means 26 Comparison means 27 Rotation speed detection means

Claims (3)

[Claims] 1. A motor power source is provided, and a motor power value at the time of the load operation in a load monitoring target machine in which idle operation and load operation are carried out is obtained, and this motor power value is within a predetermined appropriate power range. In a device for monitoring a motor load by determining whether or not it is, a storage unit that stores a motor power value during idle operation and an appropriate motor power range during load operation, and a unit that determines a motor power value during load operation And means for subtracting the motor power value during idle operation stored in the storage unit from the motor power value during load operation obtained by the means, and the subtracted power value obtained by the means in the storage unit. A load monitoring device comprising: a comparison unit that compares whether or not it is within a stored proper power range, and outputs an abnormal signal when it is outside the proper power range. 2. A motor power value at the time of load operation in a load monitoring target machine in which a load is connected by interposing a power transmission mechanism on the motor as a power source, and a load is connected to the motor. In a device that determines a torque value from the torque value and determines whether the torque value is appropriate and monitors the load, a storage unit that stores a motor specification, a motor power value during idle operation, and an appropriate torque range during load operation, Power calculation means for obtaining a motor power value during load operation, and a subtracted power value obtained by subtracting the motor power value during idle operation stored in the storage unit from the motor power value during load operation obtained by the power calculation means And a means for detecting the frequency of the motor power supply during load operation or a means for determining the rotation speed of the output shaft of the power transmission mechanism, and the obtained motor power supply frequency or output A means for obtaining a torque value during load operation based on the rotation speed of the shaft, the subtracted power value, and the motor specifications stored in the storage portion; and the torque value obtained by the means is stored in the storage portion. A load monitoring device comprising: a comparison unit that compares the current torque with the appropriate torque range and outputs an abnormal signal when the torque is outside the appropriate torque range. 3. A motor power value at the time of load operation in a load monitoring target machine in which a motor as a power source is provided, a load is connected to the motor through a power transmission mechanism, and idle operation and load operation are performed. In the device that monitors the load by determining the torque value from the torque value from the motor specifications, the motor power value during idle operation,
A storage unit that stores display scale data and an appropriate torque range on the display unit, an electric power calculation unit that obtains a motor electric power value during the load operation, and a motor electric power value during the load operation that is obtained by the electric power calculation unit. Means for subtracting the motor power value during idle operation stored in the storage unit to obtain the subtracted power value, means for detecting the motor power supply frequency during load operation, or means for determining the rotational speed of the output shaft of the power transmission mechanism And a means for obtaining a torque value during load operation based on the obtained motor power supply frequency, or the number of revolutions of the output shaft, the subtracted power value, and the motor specifications stored in the storage unit, and the torque obtained by the means. Scaling calculation means for displaying a torque value on the display unit based on the value and display scale data stored in the storage unit; and the torque value in the storage unit. Compared with proper torque range that is 憶, in the case of out of the proper torque range, the load monitoring device, characterized in that it comprises a comparing means for outputting an abnormality signal.