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MITSUBISHI CNC
(2) For servo unbalance axis
The regenerative energy differs in the upward stop and downward stop for an unbalance axis. A
constant regeneration state results during downward movement if the unbalance torque is the same as
or larger than the friction torque.
(Example)
Using a machine tool vertical axis driven by an HF154 motor, reciprocation is carried out with F30000 at
an acceleration/deceleration time constant of 100ms for a distance of 200mm. Obtain the regenerative
energy per reciprocation operation in this case.
Where:
Using expression (7-14), the upward stop regenerative energy E
RU
is as follows:
E
RU
= 5.24×10
-5
×0.85×20×3000×100 - 40 =227.2 (J)
The acceleration/deceleration distance required to accelerate at the 100ms acceleration/deceleration
time constant to 30000mm/min. is as follows:
Therefore, the constant speed travel is 150mm.
The downward stop regenerative energy E
RD
is obtained using the following expression (7-15).
Thus, the regenerative energy per reciprocation operation E
R
is as follows:
E
R
= 227.2 + 601.2 = 828.4 (J)
Regenerative energy
Upward
stop
A regenerative state only occurs when deceleration torque (downward torque) is generat-
ed.
••• (7-14)
η
T
du
N
t
d
Ec
:Motor reverse efficiency
:Upward stop deceleration torque
:Motor speed
:Deceleration time (time constant)
:Unit charging energy
(N•m)
(r/min)
(ms)
(J)
Down-
ward
stop
A regenerative state occurs even during constant rate feed when the upward torque Ts during drop-
ping is generated. Calculate so that Ts = 0 when Ts is down-
ward.
••• (7-15)
η
Ts
L
ΔS
T
dd
N
t
d
Ec
:Motor reverse efficiency
:Upward torque during dropping
:Constant speed travel
:Travel per motor rotation
:Downward stop deceleration torque
:Motor speed
:Deceleration time (time constant)
:Unit charging energy (J)
(N•m)
(mm)
(mm)
(N•m)
(r/min)
(ms)
(J)
The regenerative energy per cycle (E
R
) is obtained using expression (7-16) using one reciprocation as one cycle.
E
R
= E
RU
+ E
RD
(J)
••• (7-16)
Servo drive unit : MDS-D-SVJ3-20NA
Travel per motor rotation : 10 mm
Upward stop deceleration torque : 20 N•m
Downward stop deceleration torque : 30 N•m
Upward torque during downward movement : 3 N•m
E
RU
䋽 5.24×10
-5
T
du
䊶N䊶t
d
䋭 Ec 䋨J䋩
2T
s
L
E
RD
㧩
ΔS
㧗 5.24 ×10
-5
T
dd
Nt
d
㧙 Ec 㧔J㧕
3
0000
×100
2×60×1000
㧩 25㧔mm㧕
× 0.85× 3 × 150
E
RD
㧩
10
㧗 5.24 ×10
-5
× 0.85× 30×3000 ×100㧙40 㧩 601.2㧔J㧕
2