  The paper focuses on the stiffness modeling of a new type of compliant
manipulator and its non-linear behavior while interacting with the environment.
The manipulator under study is a serial mechanical structure composed of
dualtriangle segments. The main attention is paid to the initial straight
configuration which may suddenly change its shape under the loading. It was
discovered that under the external loading such manipulator may have six
equilibrium configurations but only two of them are stable. In the neighborhood
of these configurations, the manipulator behavior was analyzed using the
Virtual Joint Method (VJM). This approach allowed us to propose an analytical
technique for computing a critical force causing the buckling and evaluate the
manipulator shape under the loading. A relevant simulation study confirmed the
validity of the developed technique and its advantages in non-linear stiffness
analysis.
