Motoman Home Position Calibration: Tools, MotoCalV-EG, and DX200

Overview: Why Home Position Matters on Motoman Robots

Every Motoman (Yaskawa) articulated robot stores its absolute mechanical zero in a multi-turn absolute encoder backed by a backup battery. When the absolute pulse counter (APOS) data is lost - typically after encoder battery depletion, an S-axis, L-axis, U-axis, R-axis, B-axis, or T-axis motor swap, or a controlled-power-down longer than the controller's battery retention window - the controller raises a "3170 Absolute Data Lost" or similar alarm and refuses to enter play mode until the affected axis is re-mastered.

Home position calibration (also called "absolute reset," "mastering," or "zeroing") re-establishes the relationship between the motor shaft pulse count and the mechanical alignment marks. The Yaskawa Motoman ecosystem offers three escalating accuracy tiers:

1. Mechanical arrow alignment - using the cast alignment marks and red arrow stickers on each axis joint.
2. Per-model mastering pin / knockout pin set - mechanical fixtures that constrain the axis to a precise datum, used when red arrows alone are unreliable.
3. MotoCalV-EG / MOTOCAL software-based calibration - computer-assisted absolute accuracy correction, TCP measurement, and cell-level compensation.

Absolute Encoder System and Pulse-Count Drift

Each Yaskawa Sigma-series servo used in Motoman robots contains a 20-bit single-turn resolver plus a multi-turn counter. The multi-turn counter is sustained by a 3.6 V lithium backup battery pack (commonly ER14505 or a 2-cell equivalent, located inside the manipulator base or inside the battery box on the controller cabinet door, depending on the generation). Typical retention is rated for approximately 5 years with the controller powered off, but ambient temperature above 45 °C and shorted cells can collapse this to under one year.

After a battery event, the operator typically sets the home position by manually aligning the red arrows, then selecting ROBOT → HOME POSITION and writing the new pulse count. Field observation shows that even when the arrows are perfectly lined up, the recorded pulse value for the same axis can vary by several counts between attempts if the battery has not been replaced first. The root cause is residual charge in the backup circuit: the absolute counter is latching a non-zero offset each time power is removed. The corrective action is always replace the absolute-data backup battery first, then perform mastering - never the other way around.

Typical Pulse Value Drift Symptoms

Mechanical Mastering: Red Arrow Alignment Method

The red arrow method is the factory-default mastering technique and is documented in the controller's operator manual. It is also the method most often performed first on a service call because it requires no special tooling beyond a standard teach pendant and a 6 mm hex key for unlocking the brakes.

Step-by-Step Red Arrow Procedure (DX200 / FS100 / YRC1000)

1. Place the controller in TEACH mode and select ROBOT on the main menu, then HOME POSITION to open the HOME POSITIONING window. Confirm the menu path on the knowledge base article: Home Position Calibration - Yaskawa Knowledge Center.
2. For each affected axis, release the brake using the pendant's ENABLE + axis-direction deadman and manually rotate the joint until the painted red arrow on the arm lines up with the cast (machined) reference arrow on the next link.
3. Once aligned, press MODIFY (DX200 / FS100) or EDIT (YRC1000) to overwrite the absolute pulse data. The controller will display a confirmation prompt.
4. Cycle controller power. The 3170 alarm should clear and the robot should re-enter PLAY mode.

Mechanical Mastering: Per-Model Pin and Jig Sets

Red arrow alignment is only as accurate as the stamped paint line. On units that have been overhauled, repainted, or where the arrow sticker has migrated out of the casting recess, the visible arrow is not trustworthy. Motoman therefore offers model-specific mastering pin sets that mechanically constrain the joint to a datum machined into the link itself, independent of paint.

Tooling Scope by Series (Reference: Service Manual Set)

When to Use the Pin Method

• The red arrow paint is damaged, repainted, or missing.
• Multiple absolute data lost events have occurred on the same axis within 12 months (indicates the pin is the only reliable datum).
• A motor swap has been performed - the S-axis absolute count must match the new encoder's first-turn zero to within ±1 count.
• The joint was disassembled for a harmonic-drive replacement.

Sensor-Based Zeroing (Factory-Option)

Yaskawa offers a sensor-based zeroing function on certain robot models. A limit or proximity sensor is mounted to the link and detects a reference feature (lug, boss, or flag) on the adjacent link as the axis rotates. The robot's jog routine drives the axis through the sensor transition, and the controller rewrites the absolute data automatically. This is the closest functional equivalent to KUKA's Electronic Mastering tool.

Crucially, this sensor is not a field-installable upgrade. The sensor bracket is part of the link casting, and the cable routing is pre-engineered with the controller harness. If a robot was ordered without the zeroing option, the castings, cable channels, and software parameters required are absent. Retrofit is not supported. Order the option at the time of purchase if the application involves frequent motor swaps, battery service, or field-recoverable error conditions.

MotoCalV-EG Software Calibration

For applications requiring absolute positioning accuracy better than ±0.5 mm at the TCP, or for cells where mechanical arrow drift cannot be eliminated, Motoman provides the Robot Calibration Software - MotoCalV-EG toolset. The "EG" suffix denotes the Enhanced Graphics / Ethernet Generation release that communicates with the controller over Ethernet rather than the legacy RS-232 maintenance port.

MotoCalV-EG bundles five calibration utilities that improve absolute positioning accuracy, tool center point (TCP) data, and base-frame alignment:

1. Leveling calibration - corrects base-frame tilt when the robot is mounted on a non-ideal surface.
2. Zero-point master calibration - rewrites the absolute pulse counts for all six axes in a single coordinated procedure, eliminating the per-axis drift issue observed with arrow-only mastering.
3. TCP / tool-frame calibration - measures each tool's XYZ and orientation to sub-millimeter accuracy using a 4- or 5-point reference procedure.
4. Payload identification - runs an automatic inertia routine to characterize the mass, CoG, and moments of inertia of the current end-effector + workpiece, and writes these into the controller's payload table.
5. Cell-level kinematic compensation - applies a DH-parameter correction map that improves absolute accuracy throughout the working envelope, not just at the home position.

HC-Series Second Home Position

For HC-series (collaborative) controllers, the home position is supplemented by a "Second Home Position" that pairs a positional datum with a tool number. When the operator commands FORWARD to the Second Home Position, the controller moves to the stored configuration and automatically applies the corresponding tool frame, user frame, and payload parameters. This is documented in HC Series Second Home Position - Yaskawa Knowledge Center and is intended for collaborative cells that swap between two tooling configurations without operator intervention.

The Second Home Position is also affected by absolute data loss. If the master pulse data is corrupted, the Second Home Position must be re-taught after the underlying home position is re-mastered - the controller will not re-derive one from the other.

Troubleshooting Matrix

Safety Considerations During Mastering

Mastering is performed with the brake released, the joint driven by hand, and the controller in TEACH mode. The following constraints are non-negotiable:

• Verify the work envelope is clear of personnel. A free-spinning axis can pinch or strike a hand caught in the joint.
• Lock out energy to end-effectors and external axes. A gripper closing during mastering is a common cause of finger injuries.
• Use the hold-to-run / deadman switch as a fail-safe. If anything unexpected occurs, releasing the deadman will engage the brake.
• Never bypass a 3170 alarm with a software tool or by writing a "known good" pulse value from a backup. The encoder is the source of truth.

Verification Procedure After Re-Mastering

1. Cycle controller power; confirm no alarms on startup.
2. In TEACH mode, jog the robot to a known reference fixture (a dowel pin in a master plate is standard) and record the X/Y/Z position. The values should match the as-built reference within ±0.1 mm for high-accuracy cells.
3. Command a HOME move from PLAY mode. The robot should move smoothly to the calibrated zero without audible cogging or servo following errors.
4. Run a representative production program for at least 30 minutes to confirm thermal stability - harmonic drive backlash shifts with temperature, and a hot robot's home position can differ by 1-2 encoder counts from a cold robot.
5. Save a backup of the controller image (all + parameters) to external media. This is the post-mastering reference; if a second mastering is required in the future, the saved pulse values are a useful sanity check.

FAQ