2.1 Basic Structure
SMI drives fundamentally consist of the following functional units as shown in the figure.
Electric Motor
Either single-phase asynchronous motors for direct connection to
230V/50Hz networks or DC motors (LoVo) are used here.
Gearbox
The gearboxes convert the relatively small torques of the electric motors to the required
torque at the drive shaft. At the same time, they reduce the high speeds of the
electric motors to the speeds typical for sun protection drives of several
revolutions per minute.
Encoder
The encoders, also called incremental encoders, generate electrical pulses proportional to the motor speed,
which are evaluated by the electronics for speed control and
end position limiting. It is an absolute determination of the
position at any time possible.
Electronics
The electronics evaluate the signals from the encoder. In addition, the electronics determine by the
counting of the electrical pulses, the respective current position of the drive and stop it when
reaching the desired position.
SMI Interface
Communication with the higher-level
building control system takes place via the SMI interface. It can both commands be sent to the SMI drive, as well as
status messages be read from the SMI drive. Data lines and
power supply lines are guided in one line.
2.2 Application of SMI Drive Systems
Although the SMI drives have identical functional units, they differ
considerably in their mechanical design—depending on the products in which they
are used.
Blind and Venetian Blind Drives
This type of drive is installed in the head rail of blinds or venetian blinds for the
outdoor use. The drives are usually designed as center motors,
i.e., the drive has output shafts on both sides. In addition, blind and
venetian blind drives are equipped with an external limit switch for the upper end position.
Tubular drives are used in roller shutter and sun protection applications. Characteristic
here is that the sun protection elements (roller shutter slats or fabric) on a
tube are wound. The tubular drives are inserted into the tube and drive
this via appropriate adapters. The output shaft is located only on one side of the
tubular drive, on the other side the tubular drive is supported.
LoVo Drives
The LoVo drives are primarily used for interior sun protection.
Here, a small size is particularly important, as the sun protection products
for design reasons have small dimensions of the winding mechanisms.
DC motors have the advantage here that smaller sizes than with
AC drives are possible. The LoVo drives can be designed as blind drives and
tubular drives.
Window Drives / Linear Drives
SMI is increasingly used in application areas outside of sun protection.
For drives for windows, skylights or the adjustment of large louvers is a
linear movement required. Also here is the possibility of exact positioning
and the status feedback a decisive reason for the use of SMI.
SMI window drives can be designed both as mains voltage drives as well as
low voltage drives.