Home search is the procedure to synchronize the machine reference system.
This operation must be carried out when the CNC loses the machine position (e.g. by turning the machine off or if an emergency occurs).
Home Search may be done in three ways:
Homing
:
G102
directly in a G-Code program/macro/MDI.
Start Axes Homing Input
parameter of Homing
sheet from the menu Setup → Board Settings… → Inputs
.
In order to perform the Home Search procedure, the machine manufacturer has set particular points of the machine: the Machine Zero and the Machine Reference Point.
Homing: Offset
. Homing: Offset
is the difference between machine zero and the machine reference point.
Each axis can be configured to have a specific home search mode, speed, and acceleration.
The Board setting parameter Homing: Mode
in the Axes tab specifies the homing mode:
Homing: Offset
value. Homing: Direction
) until the axis meets the Homing sensor (Speed is set by Board Setting parameter Homing: Velocity
), then reverse direction, decrease velocity by a factor defined by Board Setting general parameter Velocity Divider
and when Homing sensor escapes Homing: Offset
value will be load into axis machine position. Finally, the axis is moved to Homing: Final Position
.Homing: Index Input
is set, the Homing search procedure uses also the Index Input to archive more precision. Homing: Index Input
is not permitted. Servodrive position
minus board setting parameter Homing: Offset
.
Homing: Final Position
.
Homing: Direction
) until the axis meets the Homing sensor (Speed is set by Board Setting parameter Homing: Velocity
), then a digital output is activated (selected by Board Setting parameter Homing: Pushing output
) generally used to reduce the current in the stepper motor. The axes start a movement of Homing: Pushing Position
value in the same direction to meet a mechanical lock. After that, the digital output will reset and the axis reverse direction to meet the homing sensor again as for Falling Edge mode. This mode is used when the axis step dir signals move two motors drive. The pushing movement is used to align the two axes thanks to the mechanical lock. Homing: Index Input
is not permitted.
When a Home Search is started for All axes it is possible to define the order of axis execution.
Each axis has a Board setting parameter Homing: Sequence
. Possible values are from 1 to 6.
Initially, the Home Search the Home Search is started for all axes set to Sequence 1, after axes with Sequence 2, and so on up to Sequence 6.
For a simple three-axis mill machine a typical set is Z-axis with sequence 1 and X and Y axes with sequence 2.
For every axis, it is possible to define the acceleration and the deceleration value during Home Search (see Homing: Acceleration
and Homing Deceleration
).
Please note that deceleration is important if the machine reference position is closed to a mechanical lock.
When the axis is searching the Homing Sensor at Homing: Velocity
, it will travel an extra space due to deceleration.
During this space, the axis must not meet the limit switch or the mechanical block.
To help this check the Board settings panel in RosettaCNC software calculate the Homing: Deceleration Space
according to deceleration and velocity.
Please check that axis have this space between the machine reference point and limit switch (or the mechanical block).
To save machine cost and electrical complexity it is possible to share the same sensor for the Home Search procedure and for the axis Limit Switch.
To enable this share check the appropriate settings in Board Setting Inputs as shown in the following image:
In this way when a Home Search procedure is active the Homing input acts as Homing Sensor, in other cases the Homing input is the limit switch.
Please take care that if you share the sensor it is necessary to set the Homing: Final Position
different from Homing: Offset
to avoid that at the end of the home search the sensor will not yet active and causes a LIMIT Alarm.
It is possible to use a button with a lamp to add to the CNC console the possibility to start Home Search procedure and show the Homing Done status.
To do this:
Start Axes Homing Input
according to the user input number.
Axes Homing Done
according to the user output number.
When the Home Search procedure for an axis ends, the CNC Board calculates the correction that the procedure has made to the machine position.
This value is displayed in the panel Setup → Board Monitor… → Home Corrections Space
The calculated value can be useful in two cases:
If the Home Search procedure has not been performed, dangerous conditions could occur.
In this case, the machine axis positions are not synchronized and the software limits cannot be applied.
The Allowed Commands without Homing Done
, in the menu Setup → Board Settings → General
panel, defines the CNC Board behavior in case of Home Search not executed.
Possible parameter options are:
If the CNC Board is controlling an axis with a Stepper Motor, when an ALARM occurs, the Axis Homing Search Done status will be reset.
The axis position, in the Control Software UI, will appear red-colored to indicate that the machine position could be not synchronized.
In some CNC configurations, it is never necessary to start a Home Search procedure on a single axis.
In these cases, the Homing button on the status bar can be configured to have the Home All
axes function only.
To do this set the field Homing Button Type
to Homing of all Axes
in the menu Setup → Program Settings.. → ToolBar → Geneal
sheet.
A Gantry axis is a pair of axes that, due to the way the machine is built, must move at the same time and in synchronism.
At the CNC, only the movements of one of the axes must be programmed (the master or main gantry axis).
The other axis (slave gantry axis) is not programmable.
The CNC can manage a maximum of two gantry units. In the following description, reference is made only to gantry 1.
Now we discuss and show the homing search solutions in case of Gantry axis configuration.
Please note that in a gantry configuration during the Home Search it is also necessary to perform a movement to realign the axis, so that the two motors have a position that makes the axis movement without geometric errors.
There are three gantry axis configurations:
Pushing Switch Rising Edge
mode for details.
This is a very simple configuration.
If stepper drivers support the motor current reduction by digital input, connect a RosettaCNC digital output as described in Pushing Switch Rising Edge mode.
Please note that steps for one motor revolution must be the same for the two motors.
Finally, make sure that the fault signals of the two drives are connected to the CNC.
We call one axis master gantry and another slave gantry.
When the Home search procedure is started, both motors move and the axis uses the home sensor of the master gantry.
Then the external switches are activated and only the “slave gantry” motor moves and performs its home search using its home sensor.
To do this we need two external commutators connected to one RosettaCNC User Output. A commutator when activated interrupts the signals to the master gantry stepper drive.
The second switch is a diverter and when activated the signal of the slave gantry home switch is connected to the CNC (when it is deactivated the home sensor of the master gantry is connected to the CNC).
For the configuration:
Y
sheet from the menu Setup → Board Settings… → Axes
) as usual.
Gantry 1
sheet from the menu Setup → Board Settings… → Gantries
Mode
to Use only master motor control
Master Axis
to the master gantry (for example Y
)
Homing: Mode
to Master held during alignment
Homing: Digital Output
to the User Output connected with commutators
Homing: Max Disalignment
to the maximum space that the gantry axis can be misaligned.
Homing: Switch Compensation
to zero value initially. Then if the geometry of the gantry has errors it is possible to make a small correction by modifying this value instead of moving the position of the homing sensor.
Max Disalignment
not used in case of Use only master motor control
mode.
Please note that:
We call one axis master gantry and another slave gantry.
No the external commutator is needed. Every axis has its home sensor.
For the configuration:
Y
sheet from the menu Setup → Board Settings… → Axes
) as usual.
A
sheet from the menu Setup → Board Settings… → Axes
) as usual.
A
) as Slave Axis of Gantry 1
in Machine
sheet from the menu Setup → Board Settings… → General
).
Gantry 1
sheet from the menu Setup → Board Settings… → Gantries
Mode
to Use slave motor control
Master Axis
to the master gantry (for example Y
)
Homing: Mode
to Master held during alignment
Homing: Digital Output
nor used in this case but it can be configured.
Homing: Max Disalignment
to the maximum space that the gantry axis can be misaligned.
Homing: Switch Compensation
to zero value initially. Then if the geometry of the gantry has errors it is possible to make a small correction by modifying this value instead of moving the position of the homing sensor.
Max Disalignment
used only in case of EtherCAT control.