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–1
or greater are required.
To satisfy the processing requirements of these two groups,
FANUC developed two different electric injection units.
To produce moulding products in the first group, the
injection unit is driven by a rotary type servomotor. This
can easily generate the high speed and high filling
pressure (thrust) required. On the other hand, to
produce moulding products in the second group, an
injection unit driven by a linear motor has been
developed to perform ultrahigh speed injection.
Injection unit driven by rotary
servomotor
Features of injection unit
Figure 2 shows an injection unit driven by a rotary
servomotor. Injection (screw advance/retreat) servomo-
tor and screw rotation servomotor are included.
The exclusively designed injection servomotor pro-
duces high speed (fast rotation), with high torque andlow inertia. The rotation speed is reduced by a pulley
and belt, and is transferred to a linear motion by a ball
screw.
Using a reduction mechanism, motor torque can be
amplified, which results in a high injection pressure
(thrust). Furthermore, motor rotation inertia can be
reduced by inverse proportion of the square of the gear
ratio.
A compact structure with concentration of rotation
inertia at the centre of the screw enables rapid
acceleration performance combined with a low inertia
mechanism. The injection cylinder has 1.
5 times or
greater strength of pressure resistance for instantaneous
high pressure at injection. The clamping force is
1000 kN to meet the requirement for moulds for a
cellular phone battery cell or light guide panel. In
addition, thin walled products also need only a small
injection volume. A small diameter 22 mm screw
2 Injection unit driven by rotary motor(maximum injection volume 29 cm3
) is consequently
chosen, in order to prevent material degradation as a
result of excessive residence time in the injection
cylinder.
Figure 3 and Table 1 show the external appearance
and specifications of the Fanuc ROBOSHOT S-
2000i100A electric injection moulding machine, which
has a high speed injection specification, driven by a
rotary type servomotor.
Features of control unit
As a method of improving acceleration of the servo-
motor, compensation for the mechanical delay by
providing advanced motion command is a well known
technique. However, as shown in Fig. 4, a control
method was developed for improving acceleration
performance by additional motor current. Because the
current is higher than normal, a circuit protection
function is added also taking into consideration the
heat duty in the servo drive.
With the above developments, as Fig. 5 shows, 17 ms
of acceleration time could be achieved for 0 to
300 mm s
–1
acceleration, and 71 ms of acceleration time
3 ROBOSHOT S-2000i100A high speed injection
specificationfor 0 to 800 mm s
–1
acceleration (injection flowrate:
304 cm3
s
–1
) in the Fanuc ROBOSHOT S-2000i100A
high speed injection specification machine driven by a
rotary type servomotor.
New injection unit with increased volume
The ‘Fanuc ROBOSHOT S-2000i100A high speed
injection specification’ has a good reputation for thin
walled mouldings such as cellular phone battery cells.
However, the market for products such as light guide
panels is moving to multiple cavity moulds, which
demand injection screw diameters larger than 22 mm, to
increase the injection volume.
Fanuc therefore developed the ‘Fanuc ROBOSHOT
S-2000i100B high speed injection specification’ with a
36 mm screw (maximum shot volume 147 cm3