Yaskawa YRC1000 Cubic Interference Zones for Teach Mode Safety

Overview

The Yaskawa Motoman YRC1000 controller exposes a powerful workspace-limiting feature called cubic interference that, when combined with the controller's Concurrent I/O ladder, lets you build positive safe-volume protection for Teach mode. The standard approach is to define one or more "safe" cubes where the TCP may roam freely during manual operation, then write ladder logic that monitors the cube-status bits and asserts a Hold or drops the Servo-On (SVON) request if the TCP leaves the authorized volume. This is the cleanest way to prevent an operator from jogging the arm into fixtures, fixtures-mounted tooling, light curtains, or other equipment that would otherwise be at risk during recovery from an emergency stop or program teach session.

This reference covers the full implementation path: enabling the cubic interference tables, defining the geometric cubes via the YRC1000 teach pendant, capturing the in-cube / out-of-cube status into the I/O image, building a Concurrent I/O ladder that interlocks Hold with the cube-out condition, and recovering motion with a dedicated reset path. It also covers when the Functional Safety Unit (FSU) option should be used instead of, or in addition to, software-based cube logic, and how to verify the system with a controlled commissioning test.

Prerequisites

Before starting, confirm the following are in place on the YRC1000:

• Controller: YRC1000 with firmware current to the maintenance release installed at your site. The cube-interference and Concurrent I/O features have been continuously supported across the YRC1000 product life; confirm the exact firmware label on the pendant Main Menu → System → Setup → Function.
• Robot: GP180 (or any 6-axis / 7-axis Yaskawa manipulator that supports the cubic interference table; this includes the entire GP, MH, MS, and DX-generation series that the YRC1000 supports).
• Option license: The Concurrent I/O function (sometimes labeled as "FD" in option management) must be enabled. If the ladder editor is not visible under Main Menu → Input/Output → Concurrent I/O, the option is not installed and must be activated by Yaskawa or an authorized integrator.
• Pendant: Yaskawa Smart Pendant (PHG-style) with full programming access (Management or Editor security level). Operator-level access cannot modify cubes or ladder.
• Backup: A full controller image backup via Main Menu → System → Setup → Function → Backup. Modifying ladder and cube tables should always be preceded by a verified backup.
• Knowledge: Basic familiarity with Yaskawa INFORM II job syntax, the YRC1000 I/O image (B-relay, W-relay, D-relay numbering), and ladder logic. Engineers trained only on Siemens or Allen-Bradley should expect a small learning curve: Yaskawa ladder is bit/coil/contact based, but rung scan order and I/O numbering follow the YRC1000 conventions in the Concurrent I/O manual.

YRC1000 Workspace Safety Architecture

Three distinct layers contribute to teach-mode motion safety on a YRC1000 installation, and a well-engineered system uses all three in defense-in-depth:

1. Cubic interference zones — Geometric boxes stored inside the controller that the motion planner consults every cycle. Each cube is defined by two diagonal corner coordinates (X, Y, Z) in the robot base frame, plus a class indicating whether motion into the cube is prohibited or required. Status bits reflect whether the TCP is currently inside, outside, or crossing the boundary.
2. Concurrent I/O ladder — A user-editable ladder program scanned every controller cycle (default 8 ms) that can read status bits, B-relay contact states, and operator-panel inputs, and write to outputs and control flags such as Hold, Servo-On request, and alarm annunciation.
3. Functional Safety Unit (FSU) — Optional hardware-based safety controller that monitors dedicated safety inputs (E-Stops, light curtains, safety-rated enable switches) and produces safety-rated outputs including safe torque off (STO) and safe stop. FSU is mandatory for any application where a software-only interlock would be insufficient for compliance.

The cube feature alone can be configured so that motion planning refuses to command joints into a prohibited cube. For a Teach-mode volume limiter, the typical configuration is to define a single large permitted cube (one required zone) and use the "out of cube" status bit in ladder to assert a hold whenever the TCP is at the boundary or beyond it. This gives the operator a positive envelope: movement is allowed as long as the TCP remains inside the cube, and any attempt to drive out triggers an immediate hold.

Step 1 — Define the Safe Cube on the Teach Pendant

1. Set the pendant to Management or Editor security level and switch the controller to Teach mode.
2. Navigate to Main Menu → Robot → Interference → Cubic Interference.
3. Select an unused cube number (1 through 32, depending on option; the YRC1000 supports up to 32 simultaneous cubes).
4. Choose Required Zone (the motion planner will refuse commands that leave this volume) rather than Prohibited Zone for the safe volume itself. Use Prohibited Zones for obstacles inside the safe volume if needed.
5. Jog the robot to the first corner of the safe volume, capture the (X, Y, Z, Rx, Ry, Rz) pose with Modify → Record. Repeat for the diagonally opposite corner. The YRC1000 stores the cube as an axis-aligned bounding box; orientation is not used for the volume test.
6. Set a Disable Bit address (optional) so the cube can be temporarily bypassed from a B-relay — useful for the operator "reset to recover" path described in Step 4.
7. Save and exit. Verify the table entry via Display; the controller will plot the cube overlay on the position screen.

Step 2 — Read Cube Status into the I/O Image

Every cubic interference zone exposes a set of dedicated status bits in the YRC1000 system area. The exact labels and indices are documented in the Concurrent I/O manual; the canonical bit group is typically referenced as B4A / B4B for cube "in" / "out" status. Confirm against the manual that ships with your firmware build, but the functional behavior is stable across releases:

The "in" / "out" / "boundary" bits are updated every motion-control cycle and remain valid regardless of mode. They are read-only; your ladder consumes them as contacts.

Step 3 — Build the Concurrent I/O Ladder

Open Main Menu → Input/Output → Concurrent I/O. If the editor is not visible, the option is not licensed. Yaskawa's offline tool M-LADDER can edit the same file (.LAD) in a text or graphical format and the file can be transferred to the controller; the field report thread on Mladder notes that "Mladder shows the ladder graphically but the changes need to be made in text." Use whichever method your site supports, but always back up the original *.LAD file first.

The ladder below is a minimal, representative implementation for a single permitted safe cube. It is written in Yaskawa ladder text format. Adapt the bit addresses to the ones confirmed in your manual page.

|--[ B4A0 ]--+--[ B0100 ]--( OUT  B0200 )--|   ; "Inside Safe Cube" lamp
|            |
|            +--[ B0100 ]--( OUT  B0201 )--|   ; "Operator In Teach" latched
|
|--[ B4B0 ]--+--[ B0100 ]--+--[ B0210 ]--( OUT  B0030 )--|   ; Hold request when out-of-cube in teach
|            |              |
|            |              +--[ NOT B0210 ]--( OUT  B0031 )--|  ; alarm output
|
|--[ B0101 ]--+--( RST  B0201 )--|                          ; Operator reset pushbutton
|
|--[ B0100 ]--+--( RST  B0030 )--+--[ B4A0 ]--|              ; Allow reset only if TCP is back inside

Where:

• B0100 = "Teach Mode Active" (system status input)
• B0101 = "Operator Reset" pushbutton on the operator panel (debounced in PLC input)
• B0030 = "Cube Out Hold" (wired to the controller's external Hold input via the user I/O mapping)
• B0031 = "Cube Out Alarm" (annunciator + tower light)
• B0200 / B0201 = internal status for HMI indication

The key behavior is the interlock at the bottom rung: the operator can press Reset, but the Hold will only clear if the TCP is back inside the cube. The Hold remains asserted the entire time the TCP is out-of-cube, so the operator cannot simply press Reset and continue jogging out of the safe volume. A small corrective jog brings the TCP back in, the "in" contact closes, and the reset takes effect on the next press.

Step 4 — Operator Reset and Controlled Recovery

The original question raised a concern: how does the operator recover once a hold has latched at the boundary? The answer is that the hold is conditional on the cube-out state, not latched. As long as the TCP remains outside, the hold reasserts on every cycle. The operator's only legal recovery path is to:

1. Recognize the alarm condition (tower light, pendant message, or HMI pop-up).
2. Use slow-step Teach jog (±5%, with the dead-man engaged) to move the TCP back into the safe cube.
3. Once the "in" contact is true, press the dedicated Reset button on the operator panel.
4. The hold clears, motion is restored, and the operator can continue in the authorized volume.

Servo-On vs. Hold — Choosing the Right Action

The discussion raises whether to drop the Servo-On (SVON) signal or just assert a Hold. The recommended approach for a Teach-mode volume limiter is Hold, not Servo-Off:

Cutting SVON in a teach-only violation creates a worse recovery story than a Hold and is not necessary because the controller's motion planner already prevents motion into prohibited cubes at the trajectory level. Use SVON cut only when the application demands it (for example, when the entire safe volume is configured as a required zone and any motion outside is impossible by design).

Functional Safety Unit (FSU) Integration

• Safe Torque Off (STO) on every axis with redundant hardware paths
• Safe Stop 1 (SS1) and Safe Stop 2 (SS2) with monitored deceleration
• Safe Operating Stop (SOS)
• Safely-Limited Speed (SLS) with monitored speed feedback
• Safely-Limited Position (SLP), which is the FSU-equivalent of a "cube" but with safety-rated monitoring

If your application requires the operator to enter the cell with the cell in automatic mode under reduced speed, or if compliance with ISO 10218-1 / ISO 13849-1 PL d is required, configure SLP zones in the FSU and wire the SLS to a 250 mm/s enable. The cube feature is then a soft envelope used during full-speed teaching, while the FSU is the hard envelope for all operational states.

Verification and Commissioning

After saving the ladder and cube definitions, perform a documented commissioning pass before allowing the operator on the cell:

1. Backup: Save a controller image and a copy of the *.LAD file to the engineering workstation.
2. Static test: With the robot in Teach and the TCP parked at the geometric center of the cube, verify the "in" bit is on and the hold output is off.
3. Boundary drive test: At 5% Teach speed, drive the TCP slowly toward the cube boundary along +X, +Y, +Z, -X, -Y, -Z. The hold should engage within 25 mm of the boundary on each axis, and the operator should not be able to push through with the dead-man fully engaged.
4. Reset test: With the hold engaged, press Reset. The hold should not clear because the TCP is still out. Drive back inside, press Reset, verify motion is restored.
5. Mode test: Switch to Play/Remote. The cube interlock should not interfere with normal job execution unless the job itself is configured to honor it. If the job requires motion into a prohibited cube (for example, to pick a part stored outside the safe volume), the cube is correctly configured as "Prohibited" only for Teach-mode teaching, not for production paths. Confirm the cube class and the job's path coverage before running production.
6. Power-cycle test: Cycle the controller main power. The ladder and cube table should reload from non-volatile storage. Verify the cube status bits are correct on the first scan.
7. Alarm acknowledgment: Force the cube-out condition from the I/O monitor screen, confirm the alarm text appears on the pendant, confirm the tower light pattern matches the E-Stop matrix, and confirm the HMI displays the in-cube / out-of-cube status correctly.

Troubleshooting Matrix

Best Practices Checklist

• Always back up the controller image and the *.LAD file before editing the cube table or ladder.
• Always keep one engineering-level Disable bit per cube, but never expose that bit to the operator panel.
• Use Hold, not Servo-Off, for teach-mode volume violations to preserve controlled recovery.
• Deploy the FSU option for any application with regulatory safety requirements; the cube feature complements but does not replace FSU.
• Document the cube geometry on the cell layout drawing and in the operator manual so the team can verify boundary alignment over time.
• Schedule a quarterly boundary test as part of preventive maintenance; mechanical drift or fixture changes can invalidate a previously verified cube.
• If you have multiple robots sharing a workspace (for example an ArcWorld 6200/6300/6400 cell as described in the YRC1000 Coordinated and Multiple Robot Control Group Programming Module), consider the coordinated cube tables and shared interference zones, and re-verify the boundary logic with both robots energized.

FAQ