46 / 60
g
= acceleration due to gravity (9,81 m/s²)
p
= leadscrew pitch, mm
Although the motor could produce in excess of 1 Nm of torque, we
decided to use a value of 0,4 Nm and efficiency of 0,8. This equates
to 0,4
×
3 = 1,2 Nm on the screw.
Therefore force F = 1,2
×
644
×
0,8
×
9,81/5 N
= 1212,98 N
This is far in excess of what is required on a small machine and should
result in good axis rigidity. Leaving this calculation till the end is de-
liberate, as experience has shown that, provided inertia and speeds
are sensibly chosen, it is rare to find insufficient force produced.
Note that no attempt was made to choose the smallest satisfac-
tory drive motor. We regard this as false economy and a very bad
idea on a new machine.
Here endeth the first lesson!
System description
Details are shown in
Figure 3.
Figure 3: System description.
The Galil motion controller receives an ASCII (American Standard
Code for information interchange) file from the industrial PC. There-
after, the program executes from the Galil’s onboard memory and
the PC acts as an operator interface. This avoids the use of an HMI
(human machine interface) and is by far the most efficient way to
engineer a project of this type. Standard PC literacy is all that is
required of the user.
The Galil controls the axis movement and, in addition, performs
the Programmable Logic (PLC) functions such as checking safety
circuits, and control panel pushbuttons as well as driving indicator
lamps and switched loads such as the coolant pump. In addition, an
analogue output supplies 0-10 V to control the spindle speed. Up
to eight tasks can execute simultaneously.
Figure 4
is a picture of a
typical Galil motion controller
(www.galilmc.com).
Figure 4: Typical Galil motion controller.
Programming
Commands consist of simple two letter acronyms such as:
SH X Servo Here (X axis)
BG X Begin
ST X Stop
etc
Figure 5: A Galil programming tool.
In
Figure 5
, the right hand screen is a text editor. The top left hand
screen is used to execute the program and issue commands on the
fly. The bottom left hand screen shows Galil messages and responses.
ENERGY + ENVIROFICIENCY:
FOCUS ON DRIVES, MOTORS + SWITCHGEAR
Electricity+Control
March ‘16
44