CURRENT SWITCHING AMPLIFIER
22
CEDRAT TECHNOLOGIES
Current Switching Amplifier
18/12/2017
8.3.3.Rheostatic braking
The amplifier includes energy recovery capability which is useful to recover the energy stored in electrical
element such as inductance of magnetic actuators and the mechanical energy.
Most of the time the rheostatic braking system is not necessary because linear actuators have a limited stored
energy. However, if the energy to recover is high and no braking system is present, damage on the amplifier
may happen.
The next equations are a rough estimation of the energy recovered by the amplifier (frictions are neglected).
They consider kinetic and magnetic energy:
𝐸
𝑘
= ∆𝑥 𝐹 = 𝑊
𝐸
𝑙
=
1
2
𝐿 𝐼
2
Where Δx is half of the full course, F is the maximum force. If this energy is less than 3.5J, there no need for
a rheostat.
Example:
For a MICA200, Δx = 2mm and F = 200N.
𝐸
𝑘
= 2𝑚𝑚 × 200𝑁 = 0.4𝐽
𝐸
𝑙
=
1
2
× 6𝑚𝐻 × 20𝐴
2
= 1.2𝐽
Thus, there no need for a rheostat with a MICA200.
When the computed energy is higher than 3.5J, the power of the rheostat needed is:
𝑃 = (𝐸
𝑘
+ 𝐸
𝑙
− 3.5𝐽)𝑓
The resistance value will be:
𝑅 =
𝑉
𝑏𝑢𝑠
2
𝑃
Vbus = 96V for the internal supply or 200V if an external supply is chosen.
The resistance can’t be lower than 10Ω.
It is up to the user to add margin on the ratings of the rheostat.
