Yaskawa GP8 Home Position and Second Home Position Reference

1. Overview of the Yaskawa GP8 Home Position Architecture

The Yaskawa GP8 is a six-axis, high-speed articulated robot designed for assembly, handling, and material transfer applications. The GP8 supports the IEC 61131-3 and PLCopen programming environments in addition to the native Yaskawa INFORM language running on the YRC1000 controller. The YRC1000 maintains a fixed internal reference called the Home Position and an optional user-defined Second Home Position. These positions are special in that they are tied to the controller's pulse-count origin, the absolute encoder calibration, and several safety/alarm-recovery paths.

Unlike general motion targets that the programmer defines as Cartesian positions or pulse counts in a normal job, the Home Position is reserved by the controller firmware. Yaskawa does not expose a high-level instruction that simply "go to home." Instead, the integrator must build a dedicated JOB that issues a MOV instruction to the stored home coordinates. The same approach is used for the Second Home Position, but the user must first define the position because the factory default leaves the Second Home Position unset (or coincident with the primary home position).

This reference covers:

• The functional difference between Home Position and Second Home Position
• How to create a reusable HOME JOB and a SECOND_HOME JOB
• How to call those jobs from a parent job or from a PLC-controlled cycle
• How to wire I/O interlocks that verify the robot is in a known home reference before cycle start
• Alarm 4107 recovery workflow that depends on the Second Home Position

2. Home Position vs Second Home Position: Functional Differences

From a controller standpoint, the two positions are not interchangeable. The following table summarizes the differences that drive when each is used.

The distinction matters because the controller will only allow a controlled move to Home Position when the absolute encoders still agree with pulse counts. If the encoders have lost absolute reference, the controller raises alarm 4107 and forces the operator to perform a Second Home Position recovery sequence, which is the only path the firmware accepts as valid for re-acquiring absolute position.

3. Alarm 4107 and the Second Home Position Recovery Workflow

Alarm 4107 is raised when the controller detects that one or more axes were moved while the controller was de-energized and the absolute encoder backup battery (typically a BR-series lithium cell on the S, L, U, R, B, T axis motors) has been depleted or disconnected. The pulse counter and the absolute encoder are no longer in agreement, so any move in absolute coordinates would be unverified.

The recovery workflow is:

1. From the teach pendant, navigate to ALARM and acknowledge 4107 after correcting the underlying cause (replace battery, restore wiring, re-seat connectors).
2. Place the controller in TEACH mode at reduced speed.
3. Use the pendant to manually jog each affected axis to its previously recorded Second Home Position alignment marks. The position must match the stored Second Home Position within the controller's tolerance, or absolute data is re-acquired for the axis once the alignment marks match and the operator confirms.
4. After all affected axes are matched, the controller re-establishes the absolute reference and clears 4107.
5. Cycle power, switch to PLAY/REMOTE if needed, and resume.

4. Prerequisites for Home Position Programming on the GP8

Before building the home-position JOBs, verify the following:

• Controller firmware: YRC1000 firmware is at a release that supports the second home position function block. The function is standard on current GP8 production controllers; older DX200 firmware revisions require update before the Second Home Position menu is visible.
• Tool number consistency: The tool number active at the moment the Second Home Position is taught is stored with the position. If the cycle uses multiple tool numbers, the Second Home Position must be set once per tool in environments that store it that way, or a single tool frame must be designated for the recovery motion.
• Mechanical alignment marks visible: Each axis has scribe marks on the housing and the adjacent pulley/harmonic-drive flange. Without visible marks, you cannot reliably re-master the axis.
• Free envelope: Confirm the path from the most likely parked position to the home or second home position is free of fixtures, conveyors, and operator stations. The controller does not check this for you.
• Pendant access: A Yaskawa teach pendant (typical PHC-2 or PHC-3) must be available for the initial teaching and for alarm 4107 recovery.

5. Creating a HOME Position JOB on the GP8

Although the Home Position is a reserved controller state, there is no dedicated "go home" instruction in INFORM. The integrator must build a JOB that contains a MOV instruction targeting the home coordinates. The JOB can be named anything; common conventions are HOME_POS, JOB_HOME, or GOHOME.

Step-by-step procedure (YRC1000 / DX200-class teach pendant):

1. From the job list, create a new job and name it HOME_POS. Set the job type to Robot.
2. Set the speed override to 10% (low speed) for first execution.
3. Teach a single position step at the Home Position. To do this, select TEACH > POSITION, jog all six axes to the home alignment marks (pulse count should read 0 on each axis), then ENTER to record.
4. In the job edit screen, insert a MOVL (linear move) or MOVJ (joint move) instruction referencing the taught position. Use MOVJ for a safe, joint-interpolated approach to avoid Cartesian collisions with fixtures.
5. Optionally, add a DOUT instruction before the MOVJ to set a Going Home status bit for the PLC (for example, output 20010 = ON).
6. Add a WAIT or TIMER to ensure the PLC has read the status bit before motion begins.
7. Add a DOUT after the move to set an At Home bit (for example, output 20011 = ON) when the move completes and the robot is within the in-position window.

A minimal INFORM job body looks like this in conceptual form (literal syntax follows Yaskawa conventions; consult the YRC1000 operator's manual for the exact column layout):

// JOB: HOME_POS
N000  JOB HEADER          // standard header, group 1, R1
N005  DOUT OT#(20010) ON  // "Going Home" status to PLC
N010  WAIT IN#(10050)=ON  // optional PLC permission gate
N015  MOVJ VJ=10.00 P000  // joint move to recorded home position P000
N020  DOUT OT#(20010) OFF // clear going-home bit
N025  DOUT OT#(20011) ON  // "At Home" bit set
N030  END

The position variable P000 is a local position in the job. If you want the home target to be portable across jobs, register a Position Variable in the range P1..P999 from the variable editor and reference it in the move instruction. A typical convention is to reserve P900..P909 for system positions such as P_HOME, P_HOME2, P_PARK.

6. Creating a SECOND_HOME Position JOB

The Second Home Position is taught from SETUP > SECOND HOME POSITION on the pendant, or by selecting function code 0380 from the function-code menu. The procedure is:

1. Place the robot in a safe, repeatable posture that is reachable from any realistic parked position. The integrator chooses this posture, not the controller.
2. Open SETUP > SECOND HOME POSITION.
3. Select the tool number that will be active during the recovery motion. Per the HC Series Second Home Position article, the controller stores the tool number with the position and applies the corresponding tool frame on a forward to that position.
4. Jog each axis so the mechanical alignment marks line up. Press MODIFY for each axis to latch the position.
5. Confirm and exit.

Once the Second Home Position is stored, create a JOB named SECOND_HOME with a MOVJ to that position. The JOB is structurally identical to the HOME_POS job in section 5, but it targets the Second Home Position variable. Use the same status-bit conventions to the PLC so the HMI can show "At Home 1" versus "At Home 2" if both are used.

7. Calling Home Positions from Within Another JOB

There are two principal ways to call a home-position job from a parent job in INFORM.

Method A — Direct call (CALL instruction):

// In a parent job, e.g. PALLET_01
N000  JOB HEADER
N005  DOUT OT#(20010) ON      // Going Home
N010  CALL JOB: HOME_POS      // direct sub-job call
N015  IF B001<>ON JUMP L100   // optional: verify At Home bit
N020  ... continue cycle ...

Method B — Indirect call (CALLI instruction with a job name variable):

// Indirect call, e.g. driven by a B-variable so PLC can swap targets
N005  LET B010=$B_HOME_TARGET   // string variable with the job name
N010  CALLI JOB: *B010

For a multi-recipe cell, Method B is preferred because the PLC can write the job name variable to direct the robot to a different home target for each recipe without modifying the program.

For PLCopen-style control on the GP8 IEC variant, the equivalent is the MC_MoveAbsolute or a custom function block that posts the target position variable. Yaskawa's PLCopen implementation exposes a job-call instruction that maps to CALL in INFORM.

8. PLC Interlock Design for Home Position Verification

A robust cycle-start architecture treats Home Position verification as a precondition for cycle start. The minimum recommended I/O exchange between the YRC1000 and the supervising PLC is summarized below.

Logic on the PLC side, in structured text idiom:

// Pseudo structured text (IEC 61131-3)
IF (Robot_At_Home OR Robot_At_Home_2) AND NOT Estop_Active AND NOT Alarm_4107_Active THEN
    Cycle_Start_Permit := TRUE;
ELSE
    Cycle_Start_Permit := FALSE;
END_IF;

IF Home_Request AND NOT Robot_Going_Home THEN
    Robot_Home_Cmd := TRUE;        // latched; cleared by Robot Going Home rising edge
END_IF;

The double condition (Home or Home 2) gives the cell the option to start the cycle after either a controlled homing or a 4107-recovery homing, which matches the way Yaskawa documents the recovery path.

9. Parameter Reference and Informational Variables

The YRC1000 exposes a number of system variables and parameters relevant to the home positions. The exact set depends on the firmware release; the table below is representative of the production release line for the GP8.

10. Verification and Commissioning Procedure

Commissioning a new home-position architecture on a GP8 cell should follow the sequence below.

1. Mechanical check. With the controller off, manually move each axis and verify the alignment marks are visible and clean. Replace any worn label or stamp.
2. Initial calibration. Power up, run the calibration sequence for every axis. Confirm all six axes report pulse count = 0 at the marks.
3. Teach Home Position. Record the primary home in P_HOME (P900). Record the job HOME_POS in INFORM with a MOVJ at 10% override.
4. Test in TEACH. Run HOME_POS from a different pose. Verify the path is free and the robot reaches the in-position window.
5. Teach Second Home Position. Choose a pose that is reachable from any realistic stuck position without collision. Teach it through function code 0380 and select the recovery tool number.
6. Create the SECOND_HOME JOB. Mirror the structure of HOME_POS, target P_HOME2.
7. PLC interlock test. Cycle the Home Request bit from the PLC and confirm the At Home bit returns within the expected window. Force the Cycle Start Permit low and confirm the controller refuses a new cycle start.
8. Alarm 4107 simulation. With the cell in a safe state, disconnect an absolute-encoder backup battery, power-cycle, and confirm alarm 4107 is raised. Then run the recovery flow, drive to the Second Home Position, and confirm absolute reference is re-acquired and the alarm clears.
9. Full speed qualification. With the cell guarded and the operator outside the safeguarded space, raise the speed override on the HOME_POS job to 100% and run a full auto cycle that starts with a home call.

11. Troubleshooting Common Home Position Issues

12. Best Practices for Long-Term Maintainability

• Reserve a position-variable range for system poses. Use P900–P909 for P_HOME, P_HOME2, P_PARK, P_TOOLCHANGE, and any other fixed system positions. This makes them easy to find in the variable editor and easy to back up.
• Document the Second Home Position in the cell's E-stop recovery procedure. A line operator who has never seen alarm 4107 should still be able to read the procedure and execute the recovery without calling a service engineer.
• Mirror the home status on the HMI. Show both At Home and At Home 2 as discrete indicator widgets. A single "At Home" widget hides the difference between a controlled home and a 4107-recovery home.
• Back up the job, variable, and parameter files after every teach. Yaskawa controllers support CF-card or USB backup of *.JBI, *.DAT, and parameter sets. A backup taken immediately after the home jobs are qualified is the fastest way to recover from a controller replacement.
• Re-qualify the home jobs after any mechanical work. Any change to the manipulator (motor swap, harmonic-drive replacement, brake adjustment) can shift the calibration reference. Re-teach and re-verify before returning the cell to production.