Uncontrolled vibrations may cause a large deviation from the target position and affect the dynamic performance of the endpoint in flexible robot arms. Suppression of vibrations increases the sensitivity of the endpoint in engineering applications. In this paper, the posicast control of a 4 degree of freedom mass-spring-damper system is investigated. A flexible robot arm is considered a lumped parameter system. The mathematical model of the system is obtained by utilizing the Lagrange equations. The input is the based excitation with a step function while the output is an endpoint displacement. The open loop and closed loop block diagrams are established. The input is shaped with the three step posicast technique. The natural frequency and amplitude of the free vibration response of the system are also employed for the input shaping. The shaped input is applied to the open loop and closed loop systems. Simulations are performed in MATLAB. Endpoint vibration responses are obtained with and without input shaping. The time parameters of the input shaping are determined for five different cycles as half, one-third, one-quarter, one-fifth, one-sixth of the system. The results show that the posicast technique reduces the overshoot of the system responses and provides a significant reduction in forced vibrations.