Compliant mechanisms have drawn the attention recently in developing surgical robotic manipulators for minimally invasive surgery (MIS) owing to their capabilities in making miniaturized, simple, dexterous mechanical structures. Robotically assisted MIS demands instruments with higher precision, higher output force and a higher range of motion (ROM) for better performances. On the other hand, because of the behaviour of the elastic elements, compromising these factors is challenging. In a compliant mechanism, the rigidity of the elastic element determines the precision and output force. In this paper, we study the behaviour of rigidity and the ROM of elastic elements using previously developed surgical robotic forceps based on a compliant mechanism. To tackle this problem, we studied the variation of ROM of the compliant mechanism at different rigidity values of the compliant structure by changing its thickness. The results showed the linear relationship between the ROM and the rigidity of a compliant mechanical manipulator, suggesting the optimized balance point in this trade-off.