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Application of INVT Hydraulic Servo in High Precision Grinder
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Abstract: With the development of electro-hydraulic servo technology and the expansion of industry application, servo technology grinder is becoming more and more popular. Machining industry servo grinder applications have improved the grinding accuracy of grinder and energy saving effect. Servo grinder stepless speed regulation, soft start, constant torque output have greatly meeted the requirements of mechanical processing equipment for constant speed / constant torque grinder.


Key words: high precision grinder, servo stepless variable speed, three pole rotary encoder


1. Preface


Grinder and grinding wheel motors adopted by standard machining are running according to the traditional start circuit. After starting, the motor runs according to the rated rotational speed, because the grid voltage has a certain grinder fluctuations, the friction load of grinding wheel grinder constantly changes, which will affect the rotational speed error of motor grinder.


The starting circuit of grinding wheel motor generally includes only one kind of processing speed, it is difficult to adapt to the relative line speed requirements of different grinder processing for grinder with different work piece size, so that the processing precision of work piece grinder is difficult to guarantee. Therefore, considering from the aspects of processing quality, processing efficiency, energy conservation, adopting the servo technology in grinder can receive a satisfactory grinder effect.


Machining industry grinder can process a wide range of grinder products with different work piece size and required processing accuracy. Relative grinder requires grinding wheel speed different to the spindle grinder line speed; simple grinder adjusts the spindle grinder rotational speed to meet the work piece grinder processing speed, which is difficult to reach the ideal state. Due to the grinder stress bending in the process of axis and shaft parts and different torque of grinding wheel feed grinder in the grinding process, the wheel output speed / torque will present different grinder changes, the corresponding grinder will produce vibration knife sheath/burn patterns, and the grinding accuracy is difficult to guarantee, resulting in low production efficiency, low competitive products rate and so on.


Machining industry servo grinder applications have improved the grinding accuracy of grinder and energy saving effect. Among them, the servo grinder stepless speed regulation, soft start, constant torque output have greatly meeted the requirements of mechanical processing equipment for constant speed / constant torque grinder.


2. Introduction of equipment system

Grinder is mainly composed of the bed, table, wheel frame and other components.
With the increase in the number of high-precision, high-hardness mechanical parts, as well as the development of precision casting and precision forging processes, the performance, variety and yield of grinders are constantly improved and increased.
Cylindrical grinder: it is a common type of base series, and mainly used for grinding cylindrical and conical surface. The main components include head frame, tailstock in addition to bed, table and wheel frame.

Servo system’s application in the grinder mainly refers to the application of grinder in the moving source, and it is a device to provide power and movement for executive component. 

3. Load movement characteristics

The common mechanical transmission of grinder includes belt drive, screw drive and gear drive. The transmission gear must perform tasks such as shifting, changing direction and changing the movement form, so that the actuator can obtain the desired movement speed, direction and form. 
The usage of servo system in the grinder has directly avoided the process of secondary transmission, the servo motor directly drive the wheel to obtain all the functions drive can complete.
The load in the process of grinder machining is relatively simple, the system load is in direct proportion to grinding feed. Processing is completed step by step, coarse grinding molding with large feed will be processed in the initial period, and then conduct the fine processing of 5 to 10 S feed according to the demand to make the chatter mark and smoothness on the surface of work piece reach the standard. The closed-loop speed feedback of servo system has ensured the smooth speed and stable power output.

4. Control requirements
The grinding travel of abrasive particles on the cylindrical surface of grinding wheel in the unit time is known as the wheel peripheral speed, which is expressed with v。. This speed is also the main movement speed of grinding. 
The unit of V。is m / s, and is calculated by the following formula
 
D。- grinding wheel diameter (mm);
n。 - wheel speed (r / min);
v。 - the peripheral speed of grinding wheel (m / s).
The peripheral speed of grinding wheel represents the grinding speed of grinding wheel abrasive, also known as grinding speed.
Cylindrical grinding and surface grinding speed is generally about 30 ~ 35m / s.
The peripheral speed of grinding wheel has a direct effect on grinding quality and productivity. When the wheel diameter becomes smaller, there will be a decline in the quality of grinding, that is, due to the decline in the peripheral speed of grinding wheel.
Adopting servo system can be a good way to avoid the situation above, when the wheel diameter becomes smaller, you can enhance the given speed and ensure the quality of grinding via the servo stepless speed and stable constant power output.

5. Hardware configuration
the grinder servo motor generally uses anti-oil, anti-shake, dust-proof rotary encoder which is resistant to bad environment. However, the common rotary encoders are 1 polar, and in the process of speed sampling, the feedback of speed change cannot meet the speed requirement of high precision grinder. So after trying a variety of ways, it is clear that the usage of 3 polars rotary encoder on the grinder can rapidly reflect the motor speed in real-time, and the speed fluctuation can be controlled in a better range. 


6. Electrical connection

As for the grinder processing, speed stability is an important criterion to determine the product quality, so the servo system mainly receives the speed given signal from the grinder host computer. It will feedback the signal of alarm output, fault reset, drive enable to the host computer.

7. Protection function
The application of servo system on the grinder can achieve the protection of system through the following sets of drive protection functions

code

Protection content

meaning

code

Protection content

meaning

Err01

fault

The power module instantaneously passes the short circuit current

Err02

overload

The output current exceeds the permissible operating current of the driver

 

Err03

DC overvoltage

The main circuit DC voltage is abnormally high

Err04

DC undervoltage

When the motor is energized, the main circuit DC voltage drops to the protection value below

Err05

Forward overspeed

The forward speed of servo motor is abnormally high

Err06

Module overtemperature

The heat sink of servo drive is overheated

Err07

Motor overtemperature

Servo motor winding overheat

Err08

Software fault

The servo drive software is running abnormally

Err09

CAN fault

used in debugging, the user program does not include this alarm

Err10

Environmental overtemperature

The air temperature in the drive is overheated

Err11

Self-test failure

Drive internal hardware abnormal

Err12

Task reentry

Software program call error

Err15

Pressure sensor failure

The pressure sensor wiring is wrong or itself is damaged

Err14

Reverse overspeed

In process control mode, the motor reverses overspeed

Err17

AC overvoltage

The input AC voltage is too high

Err18

EEPROM fault

Servo Unit EEPROM Data Abnormal

Err19

Enable undervoltage

When the motor is energized, the main circuit DC voltage is too low

Err20

AC undervoltage

The input AC voltage is too low

Err23

Rectifier unit failure

AC voltage does not match the DC voltage detection value

Err24

Power on timeout

Power-up relay pull-up time-out

Err25

485 communication failure

When the process instruction mode is 485 consecutive, the 485 communication abnormal driver reports the fault

 

 

 

8. Debugging points
During normal connection commissioning, conduct the normal commissioning steps (Power on> Enable disabled> Motor selection> Rotation initial angle test> Jog motor> Speed calibration> Enable on> Run). Subsequent debugging focuses on the speed to conduct fine-tuning, change the motor rotation into 3 polars rotation, coordinate with the INVT drive to control the speed deviation at plus or minus 2 rpm.



9. Introduction of product features
Advantages of INVT Servo System
1. The Product performance advantages
 INVT servo drive is the servo drive special for plastic machine, overload coefficient reaches 2.5 to 3 times; compared to the so-called servo (vector inverter) 1.5 times the overload coefficient transformed from the inverter in the market, INVT products have a unique advantage of professional servo. 
 Speed response time 30MS
2. Control the quality of products according to the control process of automobile products
2.1Comprehensive test of high and low temperature conditions
2.1Strict vibration test
2.3ISO90001 / TS16949 supply chain management process, and production process control
2.4Strict release aging test for motor and servo drive to eliminate the early failure of electronic components
2.5INVT servo products gain the European electromagnetic compatibility standard CE certification
2.6Two years quality assurance period of drive, so that customers are worry-free to regain the investment costs (energy saving / efficient)
3. Advanced motor control algorithms and injection molding control strategies
3.1 Modern motor sinusoidal vector control algorithm to achieve the perfect torque control of motor:
3.2The efficiency of the whole system is higher (system efficiency is greater than 90%);
3.3 Speed closed-loop control to ensure the speed requirements of craft process;
Conclusion:
The application of servo technology in high precision grinder has not only fully achieved the standard of original grinder technology, but also reduced the usage of the transmission part of traditional grinder application. It is a trend that cannot be neglected in the development of future grinder


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