Protection Zones

A travel limit is the outer boundary of where the machine may go. It cannot describe a tool rack standing in the middle of that boundary, because the envelope has to contain the rack: the tool changer must reach it. The obstacle is inside the permitted volume, not outside it.

A protection zone is that obstacle, declared as a volume the machine may not enter.

What a zone is

An axis-aligned box in machine coordinates, given as a minimum and a maximum on X, Y and Z, with its own Enabled. They are set on the channel, under Settings → Protection Zones.

Field	What to enter	Unit
Lower Corner (Min)	X, Y and Z of the low corner of the obstacle, in machine coordinates	mm
Upper Corner (Max)	X, Y and Z of the high corner	mm
Enabled	whether this zone is armed	none

Add Zone starts another one. The name beside it labels the row in the IDE and in the messages the IDE itself raises about the configuration; the machine does not report it.

Machine coordinates, not work coordinates: the rack does not move when a part zero is set. A box whose minimum is not below its maximum on every axis is not a volume, and it is refused rather than stored.

What happens when a move would enter one

Move	What the control does
Programmed	the block that would enter the zone is rejected before it runs
Jog	the axis is clamped at the zone face and stops there

A programmed move is checked on the volume it sweeps, not on its endpoints, so a move whose start and end are both legal is still rejected when the straight line between them crosses the zone.

Jog binds separately, because a manual move never reaches the check above. One axis is clamped at a time and the others are read where they stand. If a linear axis position cannot be read, the jogged axis freezes where it is rather than being let through. An armed zone that cannot be evaluated must not behave like one that cleared the move.

A move that starts inside a zone is allowed as long as it ends outside it. A zone narrowed after it was first authored, a changed home offset, or a machine pushed in by hand would otherwise reject the very move that recovers from it.

Jog is deliberately the stricter of the two: sliding along a zone face is refused for the axis entering it, while the same geometry passes as a programmed move. Where a zone face sits exactly on a travel limit, an axis parked on that limit would otherwise have a zero-width way around the whole zone.

Standing a zone down

Zones start armed. G22 arms them and G23 stands them down.

G23 is refused from a part program. Only a protected builder macro may switch obstacle protection off, and only for as long as that macro runs. A tool change reaching into the rack is the case it exists for. A part program that could disarm a zone would make the zone advisory rather than a guarantee.

What a zone does not cover

• Moves under tool centre point control. A zone is a volume in Cartesian machine space, which the path is not in while G43.4, G43.5, G43.8 or G43.9 is active, so the check stands down for the duration. Keep tool centre point work clear of the obstacles by program, and switch it off before a move that approaches one.
• The tool body. The check follows the gauge point, the path the spindle nose is on, not a long tool hanging below it. A tool can reach into a zone the gauge point clears, so author the zone with the longest tool in mind, or keep the retract height above the obstacle.
• Rotary axes. A zone is bounded on X, Y and Z. Jogging a rotary axis is not clamped against one.
• Anything that is not a box. A zone is axis-aligned. A round or angled obstacle is declared as the box that contains it.
• Anything that moves. A zone sits at fixed machine coordinates. A tailstock that is wound along the bed is only protected where its zone says it is.

Where to go next

• Axes & Channels: travel limits, and the rest of the channel’s settings.
• G & M Code List: G22 and G23.