Tooth by Tooth: Circular saw sharpener with ProSyCon IPC-based controller 

Some processes were already outdated in the Middle Ages, as illustrated by a scene from the past: A man is watching a craftsman who is strug-gling to cut through a beam with a saw. He calls over to him:  "Carpenter, you really need to sharpen your saw!"  "I don't have time to do that", he retorts, "I need to saw through this beam", no carpenter can afford to be so incredibly short-sighted. Apart from him, today, many engineering works and steelworks depend on sharp saw blades in their production facilities. Instead of waiting for a mobile knife grinder, industrial saws are regularly maintained by service providers that offer the appropriate equipment. The Circular Saw Service Centers from Loroch GmbH offer fully automatic machines for sharpening saw blades, in particular blades designed to cut metal. The machines are equipped with an industrial PC-based controller. 

KSC sharpening machines sharpen up to eighty different saw blades from stacks in a single run. The blade diameter (within a range of 20 to 710 mm), tooth geometry, tooth pitch and bore width can vary. In the CBN deep grinding process, which takes about fifteen minutes per saw blade, a robot arm on the machine removes a blade from the stack, swivels it round and places it on the grinding unit where it is clamped in position.

Fig.: 1

KSC series Metal Circular Saw Service Centers by Loroch can machine up to eighty saw blades in one run

The perfect finish 

To machine the saw blade, the rotating grinding wheel slowly approaches until a sensor registers contact with the tip or flank of a tooth. The controller registers the position reached, retracts the wheel slightly and rotates the saw blade by a fixed angle. The measuring process is repeated in the new position. Once all of the necessary data (blade diameter, tooth positions and dimensions etc.) has been determined, the actual grinding cycle can begin: Here, the grinding wheel with a spindle rotating at 5700 rpm is guided vertically up and down. A servo axis manages the movement of the vertical support while another axis rotates the saw blade. The feed rate reaches up to sixty sharpened teeth per minute. With the coordinated movement of the blade and the vertical support, almost any tooth shape can be generated.

Fig.: 2

3D CAD model: The up and down movement of the vertical support is aligned to match the rotation of the saw blade to sharpen it.

Traveling along a path with PC control

The machine is equipped with a SCHLEICHER ProSyCon controller as well as drives connected via CANopen. Decentralized RIO modules for inputs and out-puts are available via the bus. An industrial PC is the core of the control system. Despite well known advantages such as performance, flexibility and user-friendliness, many users have reservations about using PC technology, particu larly when used in sensitive realtime applications. A "blue screen" is all too common an occurrence and high-profile technology in particular gives good reason to be skeptical about using PC controllers for time-critical tasks: This brings to mind the delays that crashing PC control systems repeatedly cause in the ICE 3 between Nuremberg and Leipzig... The "timetable" for circular saw service centers is quite a bit more sensitive than that. Errors and delays are usually fatal: A delayed grinding wheel destroys both the saw blade and itself. A completely reliable controller is not only indispensable for precise measure-ments and distance calculations, but also in this situation. The conclusion is obvious: PC-based controllers can only be considered if they include suitable precautions that guarantee reliable operation without fail. For this purpose, Pro-SyCon systems rely on an operating system design that is tried and trusted.

Fig.: 3

Visualization and operation of ProSyCon controllers can be managed in Windows.

Right on track  

The realtime operating system VxWorks is used as a platform for the CNC core and a soft PLC - it is no coincidence that this system is used in Mars probes. The visualization and operation programmed in Pascal for the Circular Saw Service Center on the other hand runs in Windows using OPC and ensures that the ProSyCon system is both user-friendly and convenient. VxWorks only swit-ches over to Windows if the task management of the realtime operating system reports no-load operation to ensure that a change to another environment is only ever made once all realtime tasks have been completed. Windows works in its own memory area that is separate from VxWorks. This software and hard-ware design ensures that the controller works permanently without malfunction-ing. Although both operating systems run on the same processor, they do not use all of the same hardware resources: PCI and ISA cards can be assigned selectively and exclusively to one of the operating systems. Hardware interrupts that are generated by one of the printed circuit boards used by VxWorks are always registered immediately and can be processed in realtime, as they are always given a higher priority than Windows tasks and all interrupts from the plug-in cards operated by Windows.

Open to Special Know-how 

With the ProSyCon system, only the PLC part (IEC 61131) of the Schleicher controller famous for its CNC core is used - the combined CNC/PLC solution is available in the ProNumeric line as an alternative. Due to its open design, the system allows the incorporation of technology modules and simplifies the inte gration of customer-specific know-how, in particular: Loroch makes use of Car-tesian interpolation that has been created in C for the slideway and controls the servo drives in realtime via the CAN bus. Here, only the new coordinates (rela tive position) and the accelerations are transmitted to the drives which manage the position, rotational speed and power regulation. Similar solutions have also been realized for ProSyCon system with other machine tools. The digital drive interface SERCOS is also supported in addition to CANopen. Not only is it possible to connect the controllers to higher order systems quickly and easily, but internal interfaces also offer the option of remote diagnosis and maintenance without requiring additional software.

Fig.: 4

ProSyCon systems with VxWorks offer a secure operating system for realtime tasks.

Conclusion

The fully automated Metal Circular Saw Service Centers made by Loroch work quickly and precisely with their PC-based control solution. The open interfaces of the ProSyCon allow the seamless integration of separate application know-how. The system offers all the advantages of PC technology, mainly the con-venience of visualizing and operating in the Windows environment, but ensures absolute stability with VxWorks as the realtime operating system.