Soft Limits

For each axis, minimum and maximum travel values are required as part of the axis calibration process. These values are used by the system to check whether a requested motion command is within the travel limits of the axis.

If the requested motion is outside the limits, the motion is not executed and a soft limit alarm is displayed on the screen.

When setting soft limits, ensure that the machine coordinate 0 is included within the axis limits (e.g. X0, Y0, Z0, A0, B0).

The machine coordinate 0 is used for various functions. For example, Z0 is used as the position for tool changers and G28 moves.
 

Understanding Soft Limits

Soft limits define the working boundaries of the machine. They define how wide, deep, and tall the working area is. MASSO uses this information to determine if a program will move outside these limits.

Soft limits help prevent the machine from crashing at the ends of travel or into a tool changer.

Coordinate Systems

There are two coordinate systems used in CNC:

• Machine coordinates
• Working coordinates

Both can be viewed on the F2 screen:

• Large DRO values represent working coordinates
• Smaller values under the MACHINE section represent machine coordinates

Soft limits are based on machine coordinates, which are fixed after homing.

Working coordinates are used during machining and are defined in the G-code.

Soft Limit Settings

Soft limits are defined by the minimum and maximum machine coordinates for each axis.

The minimum value must always be smaller than the maximum value.

Soft Limit Alarm

If a soft limit alarm occurs, the MASSO display will indicate:

• The line number in the program
• The axis causing the issue

Use the F6 screen editor to locate the line of G-code.

Do not rely on N line numbers in the G-code file, as CAM software may use different numbering increments. Always use the line number shown in the editor.

Finding the Problem

The easiest way to diagnose a soft limit issue is to jog the machine:

• Move the axis to a safe area
• Jog the axis toward the problem direction
• Observe the machine coordinate limits on the screen

If the axis cannot reach the requested position, it means the motion exceeds the defined soft limit.

Even a very small violation will trigger a soft limit alarm.

Solutions

A common cause of soft limit alarms is tool length:

• If the tool is shorter than before, it may not reach the required depth
• If the tool is inserted further into the collet, it may reduce reach

After adjusting the tool:

• Re-home the machine
• Re-set tool zero
• Resume machining

Soft limit issues can also occur at the top of the Z axis if the tool is too long.

Material placement affects X and Y soft limits. Ensure the workpiece is positioned within the machine limits.

General Rule for Z Axis Soft Limit Alarms

• If the alarm occurs while moving down, the tool stick-out is too short
• If the alarm occurs while moving up, the tool stick-out is too long

Tool Changers

Tool changers, such as linear tool changers, can be placed outside the soft limit area.

This prevents accidental collisions during machining and jogging.

Disabling Soft Limits

Soft limits can be disabled in the machine settings.

• Disabling applies only during machining
• Jogging is still restricted by minimum and maximum travel values

Disabling soft limits prevents alarms during machining but does not stop motion beyond limits. This may result in machine crashes or damage.

Soft limits should not be disabled unless absolutely necessary. It is recommended to identify and fix the cause of the issue instead.

Hard Limits

All homing inputs on MASSO are automatically used as hard limit inputs.

• During homing, these inputs are used to locate each axis
• After homing, they act as limit switches

If triggered, a hard limit alarm will stop all motion and the spindle immediately.

Hard Limit Setup

In an ideal setup:

• The limit switch or sensor is mounted on the moving axis
• Triggers are placed at both ends of travel

This reduces the number of sensors required and simplifies wiring.

If using existing machines with sensors at both ends, the signals must be multiplexed so that a trigger at either end activates the input.

Paired sensors must be of the same type when multiplexing.

Tool Changers and Limits

Tool changers can be placed outside the soft limit area to prevent accidental collisions.

Auto Tool Zero Tool Setter

The tool setter used for Auto Tool Zero must be placed inside the soft limit area.

If it is outside the soft limit area, the machine will generate an alarm during homing when attempting to measure the tool.