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    User Guide: Actuator Mapping & Configuration Details

    This guide provides a detailed explanation of the Actuator Mapping process, including EtherCAT protocols, transmission theory, and parameter definitions.

    1. Motor Information

    This section defines the physical characteristics of the motor hardware.

    • Source: Values must be taken directly from the manufacturer's Specification Sheet.
    • Scope: Enter only the raw motor data here. Gear reducers and transmission elements are configured in a separate "Transmission" step to ensure accurate dynamics modeling.

    2. EtherCAT Settings (Advanced)

    EtherCAT settings define how the controller communicates with the servo driver. Incorrect settings here can lead to initialization failures or erratic motion.

    A. SDO Settings (Initialization Parameters)

    SDOs (Service Data Objects) are used for non-real-time configuration, typically during the startup phase.

    • Absolute Encoder Object: This object is used to clear absolute encoder errors (e.g., after battery replacement). The method of resetting varies by drive architecture.

      1. Atomic Execution Model (Supported via SDO):

        • Description: Standard drives allow the encoder to be reset by writing a single value (e.g., 1) to a designated SDO Index.
        • Action: Enter the register address here. The system will automatically trigger the reset during initialization.

      2. Transactional Execution Model (Requires Direct Connection):

        • Description: High-performance drives (e.g., Synapticon SOMANET) use a safety handshake protocol (Request → Processing → Response) rather than a simple register write.
        • Action: Leave the SDO Entry 1 field blank. Connect directly to the servo drive using the manufacturer's tool to perform the reset.

    B. PDO Mapping (Real-time Data)

    PDOs (Process Data Objects) handle periodic, high-speed data exchange.

    • RxPDO (Controller → Driver): Must include Control Word, Target Position, Target Torque, Torque Offset, Mode of Operation.
    • TxPDO (Driver → Controller): Must include Status Word, Position Actual Value, Velocity Actual Value, Torque Actual Value, Mode of Operation Display.

    Critical Warning: Verify PDO Mapping Indices

    Ensure you use User-Defined Mapping indices (e.g., 0x1600/0x1A00 for Synapticon). Using "Manufacturer Specific" or reserved areas will result in EtherCAT application errors.

    3. Transmission System (Actuator-Joint Relationship)

    The Position/Velocity commands issued to each actuator (motor) are converted through a linear transformation before reaching the robot link’s ideal joint.

    A. Overview & Terminology

    • 1 : 1 Mapping: Each actuator drives exactly one joint (e.g., Simple 2-Bar Robot).
    • n : 1 Composite Mapping: Two or more actuators share one joint (e.g., SCARA Z-axis + Θ4, or Differential Wrists).

    simple direction Figure 1: 1:1 Mapping

    multi direction Figure 2: Composite Mapping

    Term Meaning
    Gear ratio Input-shaft angle / Output-shaft angle
    Edge Value Conversion coefficient Actuator i → Joint j

    B. How to Calculate Edge Values

    The controller computes the joint vector \(q\) using the matrix \(U\):

    \[ q = U \cdot a \]

    (Where \(q\) is the joint vector and \(a\) is the actuator vector)

    Case 1: 1 : 1 Mapping (Standard)

    1. Add an edge connecting Actuator \(i\) to Joint \(i\).
    2. Enter the scale coefficient:
      • Gearbox: \(1 / \text{Gear Ratio}\)
        • Example: 1 : 50 gearbox → 1.0 / 50.0 = 0.02
      • Ballscrew: \(\text{Lead} / (2 \pi)\)
        • Example: Lead = 0.020 m → 0.02 / (2π) ≈ 0.0031831
    3. Reverse Direction: If the joint moves opposite to the command, flip the sign (e.g., -0.02).

    Case 2: Composite Mapping (Differential)

    For complex mechanisms where multiple motors drive a single axis (like a SCARA Z-axis/Theta combined), you must fill the Upper-Triangular Matrix.

    Example Matrix Form:

          ┌                                     ┐
      │ 0.02      0        0        0       │
U  =  │   0     0.02       0        0       │
      │   0       0     0.00254  0.000254   │
      │   0       0        0      0.1       │
      └                                     ┘

    This implies:

    • q3 is affected by both a3 and a4 (Main lead + Secondary mechanical offset).
    • q4 is driven by a4.

    C. FAQ

    • Q. I have a two-stage gearbox. What do I enter?

      • A. Multiply the two ratios to get the final ratio, then input 1 / (Final Ratio).

    • Q. I’m confused about the sign.

      • A. If the joint moves opposite to the command, simply flip the edge’s sign to negative.