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Application of INVT Servo System in Vertical Machining Center
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1.  Preface

Thispaper mainly introduces the application of Shanghai INVT H600 high precisionservo system as a feed drive in vertical machining center.


2. Vertical machining center
Vertical machining center refers to the machining center with vertical axis, its structure is mostly fixed column, the table is rectangular with non-indexing rotary function, suitable for processing disk, sets, plate parts, it generally includes three linear motion axis, and a rotary table along the horizontal axis can be installed in the table for the processing of spiral parts.
Vertical machining center is convenient for loading card and easy to operate or observe the processing situation; and it has easy debugging procedures with wide application. 
3. Processing center technical requirements

Table size ( W X L )

590*1450 mm

Table tee slots

18*5*125 mm

Max load of table

1350 kg

X/Y/Z travel

1270/610/760mm

X/Y/Z guideway type

滑轨

X/Y/Z Rapid speed

20 m/min

Cutting feed speed range

1~8000 mm

Distance from spindle center to vertical guideway

635 mm

Distance from spindle nose to table center

150~910 mm

Taper of spindle

ISO50

Spindle motor power

11/15 kw

Spindle speed range

20~6000 rpm

Max.output of spinder

95.4 N.m

Tool magazine capacity / type

斗笠式、圆盘式

Max.weight of tool

15 kg

Max.dia/length of tool

147 / 350 mm

Tool change time (T-T)

8 s

Position accruacy of coordinate

+0.010 mm

Repeatability

+0.005 mm

Total motor power

35 kw

Overall dimensions (LxWxH)

3200X2650X3320 mm

Weight of machine


4. Servo and host computer wiring diagram


The host computer and servo drive only rely on an industrial network cable to achieve data transmission and feedback via ETHERCAT communication, the wiring is simple with high synchronization and fast speed.


4.1 Applied EtherCAT communication of H600 Servo


EtherCAT is an open real-time Ethernet communication protocol originally developed by Beckhoff Automation GmbH. EtherCAT sets new standards for system real-time performance and topology flexibility, and it also meets or even reduces the cost of fieldbus usage. EtherCAT features include high-precision device synchronization, optional cable redundancy, and functional security protocols (SIL3). 


Operating principle:
After using EtherCAT technology, Beckhoff breaks through these system limitations of other Ethernet solutions: it is no longer necessary to receive Ethernet packets at each connection point as before, and then decode and copy them into process data. When the frame passes through each device (including the underlying terminal device), the EtherCAT slave controller reads the important data of the device.
Similarly, the input data can be inserted into the message when it passes. When the frame is passed (only a few bits), the slave recognizes relevant command and processes it. This process is implemented via hardware in the slave controller and is therefore independent of the real-time operating system or processor performance of the protocol stack software. The last EtherCAT slave in the network segment returns the fully processed message so that the message is returned as a response packet from the first slave to the master.
Terminal implementation Ethernet: Each device in the system is guaranteed to use the complete Ethernet protocol, and even each I / O terminal without the usage of sub-bus. Simply transferring the coupler's transmission medium from twisted pair (100baseTX) to E bus can meet the requirements of electronic terminal block. The E bus signal type (LVDS) in terminal strip is not dedicated and can also be used for 10 Gigabit Ethernet. At the end of terminal block, the physical bus characteristics are converted back to the 100baseTX standard.


Standard Ethernet MAC or an cheap standard network card (NIC) is sufficient for being used as a hardware in controller. DMA (direct memory access) is used to transfer data to a PC. This means that network access has no effect on CPU performance. The same principle is used in Beckhoff multi-port card, which bundles up to four Ethernet channels in one PCI slot.
Protocol: The EtherCAT protocol is optimized for process data, which is directly transferred to an Ethernet frame or compressed into UDP / IP datagrams. UDP protocol is used in the EtherCAT network segment of other subnet when the router is addressed. The Ethernet frame may contain several EtherCAT packets, each dedicated to a specific storage area, which can compose a logical process image of up to 4 GB in size. Since the data link is independent of the physical order of EtherCAT terminals, the EtherCAT terminals can be addressed arbitrarily. Broadcast, multicast and communication can be conducted between two slave stations.
In addition to the data exchange that complies with the master / slave principle, EtherCAT is well suited for communication between controllers (master / master). Freely programmable process data network variables and a variety of parameterization, diagnostics, programming and remote control services can meet various requirements. The data interface for master / slave and master / master communication is the same.


Performance: EtherCAT has reached a new level in network performance. The refresh cycle 1000 distributed I / O data is only 30μs, including the terminal cycle time. Through an Ethernet frame, you can exchange the process data up to 1486 bytes, almost equivalent to 12,000 digital I / O. And the data amount transmission is only 300μs.
Communication with 100 servo axes is only 100μs. During this time, set and control data can be provided to all axes and their actual positions and status are reported. The distributed clock technology ensures that the synchronization time deviation between these axes is less than 1 microsecond.
With the excellent performance of EtherCAT technology, control methods that cannot be achieved with traditional fieldbus systems can be implemented. In this way, a high-speed control loop can be formed via the bus. Functions that previously required native-specific hardware support can now be mapped in software. Huge bandwidth resources allow state data to be transmitted in parallel with any data. EtherCAT technology enables communication technology to match the modern high-performance industrial PCs. The bus system is no longer a bottleneck of control concept. Distributed I / O data transfer has surpassed the performance achieved by the local I / O interface.


4.2 On-site electronic control cabinet structure picture

In the test machine process, the servo drive is deliberately installed close together for testing its working performance in poor heat dissipation environment. After a long time running in the poor heat dissipation environment, H600, test results exist no problems.


4.3 Pictures of processing work piece 

The surface roughness of work piece is very good without sign of the quadrant bulge (the surface quadrant bulge due to the XY axis pass through the quadrant intersection in the process of circular interpolation). It’s the result of high response of XY axis servo feed in the whole circular interpolation process. 


Conclusion: H600 servo’s application in vertical machining center, with the usage of EtherCAT technology in the host computer, Beckhoff broke through these system limits of other Ethernet solutions, reaching a new height in network performance. Therefore, due to the height synchronization of each axis, the work piece has a great processing effect in the machining process, it will be a new breakthrough of drive feed direction in the field of machine tool processing.






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