Pneumatic actuation
SITEMA - Safety Brakes
Technical Information
TI-B10-EN-04/2009
SITEMA GmbH & Co.KG . Im Mittelfeld 10 . D-76135 Karlsruhe . Phone: +49 (0)721 98661-0 . Fax: -11 . www.sitema.com 2/3
Acting force does not exceed the nominal load M, the movement
of the rod is very small, typically under 0.5 mm. The position
of the clamping ring remains in its original position,
because the spring force V (4) is somewhat larger than M (see
Fig. 1).
Dynamic braking of a falling mass
Fig. 3: Clamped and overloaded, i.e. dynamic braking force substantially
larger than nominal load
If a moving mass has to be stopped, the kinetic energy has to
be dissipated by friction.
For the clamping system, this means that the dynamic forces
become much higher than the static forces. If the load exceeds
the spring force V (4) Fig. 4, than the whole package (clamping
ring (2) + clamping sleeve (1) + annular piston (5)) moves together
with the rod until it gets to the mechanical stop after approx.
2 mm. The spring (4) then bounces slightly, without
reaching the block storage area. The clamping force cannot increase
after this point.
The slipping force for the rod is thus limited and predictable, lying
between 2 and 3.5 times M. The resulting deceleration (if
load is equivalent to M) is thus between g (gravity) and 2.5xg.
The shaded area under the force-deflection curve represents
the dissipated energy.
After stopping, the spring (4) will again raise the mass by a
small amount.
Fig. 4: Force-deflection diagram
Releasing the clamping
If the rod did not move after clamping and therefore no load is
was transferred to the
safety brake, the clamp may be opened
by simply applying the operating pressure.
However, if the clamp is to be released while the KSP Safety
Brake is holding a load, an upward movement of the rod is normally
necessary additionally to the release pressure at port L.
Thus providing the safety advantage that the clamp can generally
only be released as far as the hoist drive is intact and controlled.
However this advantage does not necessarily apply to small
loads with a simultaneously high release pressure (for details
see minimal loads F6 in „Technical Data Sheet TI-B11“).
A standard proximity switch has to be used to indicate signal 2
"Clamping released".
Upward movement
The release pressure should normally be enabled for all upward
movement, as the rod can then move freely.
Upward movement while clamped (without release pressure) is
possible. The friction force then achieves approx. 15-20% of M,
which effect can principally be used for an emergency-stop in
upward movement. In normal conditions, the
safety brake
should always be released during upward movement.
Downward movement
Downward movements are only possible when and as long as
signal 2 „released“ is activated,, it is therefore imperative that
this signal be processed accordingly in the control unit.
3 Control
Fig. 5: Schematic diagramm of pneumatic circuit
* If the pressure (p) is not suficiently constant (e.g. pressure drop at
the beginning of lowering movements) we recommend a check valve
in the p connection of the valve.
Under no circumstances may the outflow of the medium from
connection L be hindered by any additional components.
JAll connection lines must be laid out without kinks. If
there is any danger of kinking appropriate precautions
must be taken (protective tube, thicker hose etc.)
Pressure medium
The compressed air must be dried and filtered
Activation using 3/2-way valve
In most cases, the activation indicated in Fig. 5 will be used.
During every operational cycle, the 3/2-way valve is actuated
electrically and releases the KSP Safety Brake.
Load direction
6
1
2
4
5
3
approx. 2 mm
approx. 0.5 mm
deflection
Part 5 at mechanical stop
Force
pre-tension V
of spring (4)
rated load M
dissipated
energy
* )
p
