This OPC UA ObjectType represents a CNC channel with all its necessary elements. All Objects of Type CncChannelType are listed in the CncChannelList of the CncInterface Object.
Additionally to data that is relevant for a CNC Channel, CncChannelType organizes Objects of type CncAxisType and CncSpindleType. That is to indicate which components are currently administrated by this channel.
Objects of CncChannelType may generate two kinds of events: Events of type CncMessageType and of type GeneralModelChangeEventType.
Events of Type CncMessageType are used to provide channel specific messages that are not an alarm but an uncritical information, e.g. a user created message out of the CNC part program.
Events of type GeneralModelChangeEventType are used to inform about changes in the Information Model. Examples for the need of a model change event:
- A CNC channel can administrate a different set of components during runtime, meaning that an axis or a spindle can change its channel affiliation during runtime of the CNC system; for instance this may be the case if one spindle is used in combination with different axis groups.
- Spindles allow different kind of operation modes, for instance a spindle can change its mode of operation from speed to position control and therefore has to be represented once as spindle (CncSpindleType) and once as rotational axis (CncAxisType). Instances of CncChannelType provide the position of the channel’s tool center point in different coordinate systems. Therefore, the following definitions have to be considered:
Tool carrier zero point: The tool carrier zero point is a reference point on the tool carrier as illustrated in Figure 10.
Figure 10 – Tool carrier zero point for milling and turning tools
Tool center point: The tool center point of tools for milling operations is usually the intersection of the tool centerline and the lowest positioned cutting tip (edge). For turning operations the tool center point is an imaginary tool point of the cutting insert, because most tools have a cutting edge with a built-in radius. The tool center point of point-to-point tools, such as drills, is the extreme tip of the tool, as measured along the Z axis. Figure 11 and Figure 12 illustrate some common tool center points.
Figure 11 – Example tool center points for milling tools
Figure 12 – Example tool center points for turning tools
Machine tool coordinate systems: This companion standard refers to two coordinate systems (see Figure 13 for illustration):
- Base coordinate system: The base coordinate system (BCS) is a coordinate system defined by the machine tool manufacturer. It has its origin within the machine tool’s zero point M.
- Workpiece coordinate system: The workpiece coordinate system (WCS) is a user defined coordinate system and allows considering the clamping position and orientation of a workpiece. It has its origin within the workpiece zero point W.
Figure 13 – Machine tool’s coordinate systems and reference points
The coordinate systems are built based on the right-hand-rule, illustrated in Figure 14.
Figure 14 – Coordinate systems: positive directions and orientations (DIN66217)
Figure 15 – CncChannelType