Rotation Tool Center Point

The concept of Rotation Tool Center Point (RTCP) is a crucial feature in multi-axis CNC machining, particularly for 5-axis machines. It allows the tool to maintain a consistent orientation relative to the workpiece, even as the machine’s axes move. This is essential for achieving precise machining results on complex, three-dimensional parts.

Key Points about RTCP

1. Definition:
   • RTCP enables the tool to rotate around a fixed point in space, known as the Tool Center Point (TCP). This point is typically the tip of the cutting tool.
   • The TCP can be defined in the machine’s coordinate system, and the tool’s orientation is adjusted dynamically as the machine moves, ensuring that the tool tip follows the programmed path accurately.
2. Advantages:
   • Precision: RTCP ensures that the tool tip follows the programmed path with high precision, even when the tool is tilted or rotated.
   • Flexibility: It allows for complex machining operations, such as milling at various angles and orientations, which would be difficult or impossible with traditional 3-axis machining.
   • Efficiency: By maintaining the correct tool orientation, RTCP reduces the need for frequent tool changes and manual adjustments, leading to more efficient machining processes.
3. Programming Considerations:
   • Tool Length Compensation (TLC): This function adjusts the tool length to ensure that the TCP remains consistent, even if the tool length changes (e.g., due to wear or tool change).
   • Tool Radius Compensation (TRC): This function adjusts the tool path to account for the tool’s radius, ensuring that the tool tip follows the exact programmed path.
   • Coordinate Systems: RTCP often involves the use of multiple coordinate systems, including the machine coordinate system (MCS), workpiece coordinate system (WCS), and tool coordinate system (TCS).
4. Implementation:
   • Activation: RTCP is typically activated using a specific command in the CNC program, such as #TRAFO ON or #TRAFO OFF to enable or disable the transformation.
   • Configuration: The TCP and other parameters must be correctly configured in the CNC control system. This includes setting the tool length, tool radius, and other relevant parameters.
   • Monitoring: The CNC control system continuously monitors the tool’s position and orientation, making real-time adjustments to maintain the TCP.

How to use RTCP in Fanuc CNC?

1. Activate RTCP: Use the G code G43.4 to activate RTCP.
2. Set the tool length compensation: Use the H code (e.g., H10) to specify the tool length compensation value.
3. Program the tool path: Define the tool path using standard G codes for linear and circular interpolation.
4. Deactivate RTCP: Use the G code G43.5 to deactivate RTCP when finished.

Example Program:

%RTCP_Example
N10 G90 G00 X0 Y0 Z0        ; Rapid move to start position
N20 G43.4                    ; Activate RTCP
N30 G01 X100 Y50 Z-20 F500  ; Linear interpolation
N40 G02 X150 Y100 Z-30 I50 J0 F500 ; Circular interpolation
N50 G43.5                    ; Deactivate RTCP
N60 M30                      ; Program end

Key Parameters for RTCP:

• Tool length compensation: Set using H codes (e.g., H10).
• Rotation axis center: The center of rotation for the axes (e.g., A, B, C) must be defined in the machine parameters.

Applications:

RTCP is ideal for complex 5-axis machining tasks, such as:

• Aerospace components: Machining turbine blades and other complex shapes.
• Precision engineering: Ensuring high accuracy in intricate parts.

By using RTCP, you can achieve efficient and precise 5-axis machining, reducing programming complexity and production costs.

In Heidenhain CNC systems, Rotation Tool Center Point (RTCP) functionality ensures precise tool positioning during multi-axis machining by compensating for rotary axis movements. Here’s how it works and its implementation:

Key Features in Heidenhain CNC:

1. Activation via M128 Code
   Heidenhain uses the M128 command to enable RTCP mode, analogous to Fanuc’s G43.4 . This allows the control to dynamically adjust the tool’s position to maintain the programmed center point relative to the workpiece during rotations.
2. Integration with Kinematic Models
   The TNC 640 control, for example, employs kinematic modeling to account for the machine’s specific rotary axis configuration (e.g., tilting spindle or rotating table). This ensures real-time compensation for angular changes .
3. Tool Measurement and Data Accuracy
   Heidenhain systems rely on accurate tool geometry (length, radius) stored in the tool table. Tools like the HEIDENHAIN TT touch probe automate tool measurement, ensuring precise input data for RTCP calculations .
4. Collision Avoidance
   The TNC 640’s RTCP functionality includes collision monitoring, leveraging predefined machine kinematics to prevent interference between the tool, spindle, and workpiece during complex 5-axis movements .

Practical Implementation:

• Programming: Use Heidenhain’s conversational programming (e.g., TNC 640) to define toolpaths with RTCP enabled via M128. The control automatically adjusts linear and rotary axes to maintain the tool center point .
• Applications: Ideal for aerospace and mold-making, where maintaining precise contact with complex surfaces is critical .

Example Workflow:

1. Measure the tool using a HEIDENHAIN TT probe to populate the tool table with exact dimensions .
2. Activate RTCP with M128 in the NC program.
3. Program the toolpath using the workpiece coordinate system; the TNC 640 handles rotary axis compensation dynamically .

Note: Heidenhain’s RTCP implementation emphasizes seamless integration with its hardware (e.g., touch probes) and software (kinematic models), reducing manual adjustments and enhancing precision .

Here’s an example of a Heidenhain CNC program using M128 for RTCP (Rotation Tool Center Point) control, based on typical workflows and references from the knowledge base:

Example Program: 5-Axis Machining with RTCP (M128)

BEGIN PGM 5AXIS_EXAMPLE MM
1. TOOL CALL 1 Z S4000        ; Select tool T1 (e.g., Ø10mm end mill) 
2. L M6                       ; Tool change
3. M3                         ; Spindle ON (clockwise)
4. M7                         ; Coolant ON
5. M128                       ; Activate RTCP mode 
6. CYCL DEF 247 TCPM          ; Optional: Define TCPM parameters (if supported) 
7. L X0 Y0 Z10 R0 B0 C0 FMAX ; Rapid to safe position (B/C axes at 0°)
8. L Z-5 F200                 ; Plunge to cutting depth
9. APPR CT X10 Y10 Z-5        ; Approach arc center (RTCP adjusts for B/C rotations) 
10. FC DR+ CPA+180            ; Circular interpolation (full circle)
11. DEP CT X10 Y10 Z-5        ; Depart arc
12. L Z10 FMAX                ; Retract
13. M9                        ; Coolant OFF
14. M5                        ; Spindle OFF
15. M30                       ; Program end
END PGM 5AXIS_EXAMPLE MM

Key Notes:

1. M128 (RTCP Activation):
   Enables RTCP mode, ensuring the tool center point remains fixed relative to the workpiece during rotary axis movements . This compensates for kinematic shifts caused by B/C rotations.
2. Tool and Workpiece Setup:
   • Tool data (length/radius) must be pre-measured using a HEIDENHAIN touch probe for accuracy .
   • Workpiece coordinate system (e.g., CYCL DEF 247 TCPM) defines the TCP frame .
3. Motion Commands:
   • Lines 9–11 use circular interpolation (FC) with RTCP compensation. The control adjusts linear/rotary axes dynamically to maintain the tool’s cutting point .
   • Rotary axes (B/C) are programmed in degrees (e.g., B45 for 45° tilt) but omitted here for simplicity.
4. Collision Avoidance:
   • The TNC 640 (with RTCP) automatically checks for collisions between the tool, spindle, and machine components .

Practical Considerations:

• Post-Processor Setup: Ensure the CAM system outputs RTCP-enabled code with M128 and correct coordinate transformations .
• Kinematic Configuration: The machine’s rotary axis kinematics (e.g., tilting table vs. spindle) must be defined in the TNC control .
• Legacy Systems: Older controls like the TNC430 may require manual adjustments or lack advanced TCPM features .

For complex 5-axis paths, use Heidenhain’s conversational programming or CAM software (e.g., HEIDENHAIN MillPlus) to generate RTCP-optimized toolpaths .