Tormach PCNC 770 - Page 203

Chapter 10
203
UM10350_PCNC770_Manual_0916A
Troubleshooting
A full wave bridge recer on the DC bus board in conjuncon with a 15,000 μF (micro-Farad)
capacitor connected (wires 300 {common} and 301) to the DC bus board provide a nominal 65 VDC
supply for the electronic driver modules which can be measured on wires 300 and 301. This supply
is individually fused for each axis and distributed to each axis. See Table 4.4.
Control signals to move the axes are created by the PathPilot controller. The controller sends the
axis commands via the mill interface board to the main control board, which processes these signals
and distributes them to the individual axes through a ribbon cable plugged into the axis drivers.
The X- ,Y-, and Z-axis each has one limit switch which actuates at the end of travel in each direcon.
These limit switches are used to stop the travel of an axis before the mechanical limit is reached. The
limit switches are also used to stop an axis near its extreme travel posion in a reference procedure.
Sensors such as limit switches are the most common source of problems on a mill. By necessity
they need to be mounted where they are detecng events such as end of travel. This makes them
vulnerable to damage. They can get fouled by coolant, chips, or by physical contact. Scking and
wire damage are also common problems.
PCNC mill electronics are such that if any one limit switch is actuated, or the control board thinks
the switch is actuated, the mill will not come out of reset. In order to temporarily work around a
faulty limit switch, you may check the Disable Home Switches checkbox on the Sengs tab. This will
allow you to jog the mill to the home posion and reference the axes manually by pressing the Ref
buons. This will establish so limits, and allow you to use the mill unl you repair the faulty switch.
The limit switches are all wired normally closed. Therefore, a broken wire or defecve connecons
results in the control board detecng a limit switch is actuated. The diagnosc screen shows the
status of the switches.
The axes are driven by axis motors that have no feedback. It is possible that an axis can be commanded
to move but will not move as far as it is commanded to. This is commonly referred to as losing steps.
Excessive fricon or load in the mechanical system will cause the loss of steps. When losing steps it
is usually possible to hear a cogging noise from the motor. The probability of losing a single step or
a few steps from a mechanical problem is very low. Mechanical issues most oen result in losing a
large number of steps or stalling the motor.
Addional Notes on Lost Steps
In the spirit and philosophy of this guide, divide and conquer has no beer applicaon than in
the case of trouble shoong loss of posion, or lost steps. As a general rule, a properly operang
PCNC mill being used in overloaded cung situaons should experience a spindle stall (or a broken
cung tool) long before an axis sees so high a cung force that it stalls or skips. Keeping this in
mind, it is worth menoning that the vast majority of problems that are mistakenly associated with
lost steps are actually due to one or more of the following:
• Improper use or call-out of mill osets such as G54/55, as well as G43
• Tool pull out as a result of a cuer or holder not secured properly