How to Set the Zero Point on a Mitsubishi CNC (M70 / M80) — Absolute Position Initialization

Mitsubishi M70 and M80 controls raise alarm Z71 (absolute position lost) or Z70 (absolute position initialization incomplete) after a battery failure, encoder replacement or motor swap. Production cannot restart until the zero point is re-initialized. Here is the complete procedure, using the control's built-in Absolute Position Setting screen.

Before you start

• Know which initialization method your machine builder used: marked point (align to a scribe mark), machine end / stopper (push against a mechanical stop), or dog-type. Marked point is the most common on machining centers.
• If a Z71 appeared after battery change, replace the battery first — initializing with a dead battery will just lose the position again at the next power off.
• Clear the work area; the axis will be jogged across its travel.

Marked-point initialization procedure

1. Open Maintenance → enter the password (usually MPARA or the builder's code) → select Abs pos set (Absolute Position Setting screen).
2. Select the axis to initialize. Set #0 Absolute posn set = 1. The state display shows [AX. NOT COMP].
3. Set #2 Zero-P to the builder's zero-point offset value if specified (from the machine data sheet), otherwise leave 0.
4. In handle mode, jog the axis until the alignment marks on the slide and the way cover / casting line up exactly. Use the 1µm handle increment for the final approach.
5. Set #1 Origin-P = 1. The state changes to [ORIGIN SET] and then [AX. COMP] — the zero point is stored.
6. Repeat for each axis showing Z71.
7. Power the control OFF and back ON. Confirm no Z70/Z71 alarm and that the machine position reads correctly at the marks.

Stopper (machine end) method — quick notes

1. On the same screen set #0 = 1, then select the stopper method (parameter #2049 Type = 3 on most builds).
2. Start the cycle; the axis pushes against the mechanical stop at low torque twice, and the control computes the zero point from the stop position plus the builder's offset.
3. Complete with power OFF/ON as above.

Common problems

• Z71 returns after power off — battery flat, battery cable open, or encoder backup circuit faulty. Measure the battery: below ~3.2 V (single cell) replace it.
• [ORIGIN SET] will not accept — check the axis is in handle/jog mode and the servo is ON (not in emergency stop).
• Position off by a few mm after initialization — wrong #2 Zero-P offset; pull the correct value from the builder's documentation.
• Z70 remains after completing all axes — one axis (often a rotary or the spindle C-axis) still uninitialized; check every axis on the Abs pos set screen.

Related guides

• How to replace a Mitsubishi CNC battery
• Mitsubishi M70 / M80 alarm list
• Forum: Z71 after battery change — restore without a crash