Deactive Prismatic Joint in SimMechanics

Hi there,

i have a prismatic joint in my robot model which i would like to deactivate under certain conditions (making it a weld "joint"). I found several similar problems (for example http://www.mathworks.de/matlabcentral/newsreader/view_thread/59528), but the given solutions don't help.

Here is what i tried:

1. Put a joint sensor behind the prismatic block 2. Feed a joint actuator with the joint sensor signals and apply it to the prismatic joint (Actuate with Motion option activated).

This results in a weld block, but it is not interactive. What i need is some kind of enable-signal which activates or deactivates the actuator. I tried to put the sensor/actuator in an enabled subsystem but this doesn't work because a hierarchy doesn't seem to be allowed here.

Has anyone an idea how to solve the problem?