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Figure 1: Someone is using the VFD.

The Variable Frequency Drive (VFD) is a device widely used to convert the constant voltage of an autonomous AC power source into a variable voltage for controlling the torque and speed of the motor. They are ideal for motors that drive loads on mechanical equipment. A VFD offers higher efficiency than simple inline motors, as well as a degree of control not available with simple drive motors. These factors can save energy costs, improve production performance and extend motor life.

Challenges of VFD

The VFD is also known as VSD and ASD. Troubleshooting and testing are usually performed by experts using a variety of test instruments, including oscilloscopes, multimeters, or other tools. These tests may involve some degree of trial and error using the ancient method of elimination. Because of the complexity of the motor system, testing is usually done once a year unless the system starts to fail. Given that equipment often lacks or has an incomplete record, it’s difficult to determine where to start testing. This includes recording specific tests and measurements performed previously, the completed work, or the individual components after adjustments. Advances in testing technology have solved some of the challenges. New instruments such as the Fluke Motor Drive Analyzer (MDA-510 and MDA-550) are designed to make VFDs more efficient, and to document the process step by step. These reports can be saved and compared with subsequent test results for a more complete understanding of the motor driver's maintenance history.

Figure 2: The Fluke Motor Drive Analyzer.

Figure 1: The tire pressure monitoring system.

Automotive sensors are the fastest growing and most used type in recent years. The development of the automotive industry stimulates the improvement of automotive pressure sensors. Advanced manufacturing and process technology strengthen the performance of sensors, and tire pressure monitoring is increasingly accurate. At present, in order to ensure the safety of driving, most car tires are equipped with pressure sensors to detect pressure change. When the tire pressure reached a reasonable value, it can improve safety, but also can save fuel consumption, according to the relevant data statistics.

Tire Pressure Sensor Working Principle

Tire pressure monitoring system (TPMS) mainly has two kinds of solutions, direct system and indirect system. A direct tire pressure monitoring system is the use of pressure sensors installed in each tire to directly measure the tire pressure, and display and monitor it. When the pressure is too low, the system will automatically alarm.

Indirect TPMS

As for the indirect tire pressure monitoring system, the wheel speed sensor of the automobile ABS system compares the speed difference between tires, so as to achieve the purpose of monitoring tire pressure. And the main disadvantages lie in the following three aspects. The exact instantaneous pressure of each tire cannot be displayed. It can not alarm when the pressure of the same axle or wheel on the same side or all tires drop at the same time. The factors such as speed and detection accuracy cannot be taken into account simultaneously.

Direct TPMS

The direct tire pressure monitoring system is divided into two types that are active and passive. * Active System The active system is achieved by using mems technology on silicon capacitive or piezoresistive pressure sensors. The pressure sensor is installed on each wheel rim, transmitting a radio frequency signal. Then the wireless receiver installed in the cab receives the pressure sensor signals, after a certain signal processing, and shows the tire pressure. The active system is a relatively mature technology, and the developed module can be applied to the tires of various brands. But its disadvantage is also prominent, whose induction module needs battery power, so there is a problem of service life.

Figure 2: Some tire pressure sensors.

* Passive System The sensor of the passive tire pressure monitoring system is designed by a surface acoustic wave, and it produces a surface acoustic wave through a radio frequency electric field. When the surface acoustic wave reaches the surface of the piezoelectric substrate materials, there will be changes. By detecting the change, the tire pressure is known. Although this type of technology does not need battery power, it requires transponders to be integrated into tires, requiring common standards from tire manufacturers. The monitoring system can detect the abnormal condition of tire pressure only with high resolution. Battery life is limited, and capacity is also affected by temperature. In order to improve the reliability of the monitoring system, it is better for the sensor to carry out passive detection. The research shows that the information collected by a tire pressure sensor can be used to monitor the fault of the vehicle suspension system and correct the navigation system.

Figure 1: Cutaway 3D model of a car AC compressor.

Cylinder Block and Cylinder Head Repair

Using a straight edge and a feeler gauge to examine the flatness error between cylinder head, cylinder block, crankcase and bottom cover, which should not be more than 0.05mm, otherwise, you should grind it. If there are cracks in the cylinder block and cylinder head through observing or knocking, replace them with new ones.

Cylinder Wear Repair

Use the cylinder gauge to check the wear condition of the cylinder. If the cylindricity error is more than 0.25mm and the roundness error is more than 0.08mm, you should bore and grind the cylinder. The boring and grinding operation shall be carried out according to the repair dimension, generally divided into five grades and each step shall be increased by 0.25mm. When the cylinder is bored to the last-level repair dimension, you can repair it by reinserting the sleeve. When you insert the case, the interference of the matching shall be 0.05mm ~ 0.12mm.

Crankshaft Repair

Through visual inspection, if you find cracks on the crankshaft, replace it with a new one. If the clearance between crankshaft journal and ball bearing is more than 0.02mm, you could repair the journal by chromium plating or surfacing welding, or replace it with new parts. If the roundness error of the connecting rod journal exceeds 0.10 mm, you should ground the connecting rod journal or replace it. If the limit wear is exceeded, you must replace the connecting rod journal.

Repair of Connecting Rod Group of the Piston

The piston connecting rod group includes a piston, a piston ring, a piston pin, and a connecting rod. If the connecting rod is bent, you should correct it. If there are cracks, replace the connecting rod with a new one. The new piston shall meet all technical standards. The matching clearance between the new piston and the cylinder is 0.03mm-0.09mm. When the fit clearance between connecting rod bearing and journal exceeds 0.12mm, use a new bearing instead.

Figure 2: Connecting rod group of a piston compressor manufactured by Kawasaki, including connecting rod, piston, piston pin, etc.

Figure 1: Cutaway 3D model of a car AC compressor.

Cylinder Block and Cylinder Head Repair

Using a straight edge and a feeler gauge to examine the flatness error between cylinder head, cylinder block, crankcase and bottom cover, which should not be more than 0.05mm, otherwise, you should grind it. If there are cracks in the cylinder block and cylinder head through observing or knocking, replace them with new ones.

Cylinder Wear Repair

Use the cylinder gauge to check the wear condition of the cylinder. If the cylindricity error is more than 0.25mm and the roundness error is more than 0.08mm, you should bore and grind the cylinder. The boring and grinding operation shall be carried out according to the repair dimension, generally divided into five grades and each step shall be increased by 0.25mm. When the cylinder is bored to the last-level repair dimension, you can repair it by reinserting the sleeve. When you insert the case, the interference of the matching shall be 0.05mm ~ 0.12mm.

Crankshaft Repair

Through visual inspection, if you find cracks on the crankshaft, replace it with a new one. If the clearance between crankshaft journal and ball bearing is more than 0.02mm, you could repair the journal by chromium plating or surfacing welding, or replace it with new parts. If the roundness error of the connecting rod journal exceeds 0.10 mm, you should ground the connecting rod journal or replace it. If the limit wear is exceeded, you must replace the connecting rod journal.

Repair of Connecting Rod Group of the Piston

The piston connecting rod group includes a piston, a piston ring, a piston pin, and a connecting rod. If the connecting rod is bent, you should correct it. If there are cracks, replace the connecting rod with a new one. The new piston shall meet all technical standards. The matching clearance between the new piston and the cylinder is 0.03mm-0.09mm. When the fit clearance between connecting rod bearing and journal exceeds 0.12mm, use a new bearing instead.

Figure 2: Connecting rod group of a piston compressor manufactured by Kawasaki, including connecting rod, piston, piston pin, etc.

Figure 1: Servo motor is a core part of servo system.

With the development of information, communication and automation technology, a wide variety of automatic control devices have been used in industry production and daily life of modern world. As one of the most common devices for automatic control, servo system, constituted by servo motor and servo drive has been widely used in our daily life. With our article here, you can get a deeper understanding where exactly can servo motor and servo drive can be used.

1. What is Servo System?

Servo system, is a feedback control system used to accurately follow or reproduce a process. As one of the key components of a servo system and the execution part of it, servo motor changes the object's position, orientation, state and other output controlled quantity following the input (or a given value). Its task is to amplify, transform and regulate the power according to the requirements of the control command, so that the output torque, speed and position control of the driving device is very flexible and convenient.

2. Components of Servo System

The system is mainly composed of HMI touch screen, PLC, servo drive, permanent magnet synchronous servo motor. The servo motor is the executive mechanism of the movement. It does position, speed and current control, so as to meet the user's functional requirements.

Figure 2: Servo system is composed of PLC, drive, motor, reducer and interface.

3. Features, Uses and Types of Servo System

3.1 Features of Servo System

It needs accurate detection device to compose closed speed and position loop.

Various Feedback and Comparison Principles

There are a variety of feedback comparison principles and methods. According to the different principles of detection device to achieve information feedback and different methods of feedback comparison, there are pulse comparison, phase comparison and amplitude comparison in common use.

High Performance Servo Motor

In NC machine tools for efficient and complex surface processing, the servo system will often be in the process of frequent start and brake. So the ratio of the motor's output torque to the moment of inertia is required to be large enough to generate a large acceleration or braking torque. And also the servo motor is required to have large enough output torque at low speed and smooth operation, so as to minimize the intermediate link in the connection with the mechanical moving part.