The manipulation phase of a multifingered robot hand is initialized, upon contact, by the impact force patterns imparted to the object at contact points, in the final state of a preshaped hand closure. The object then inherits from contacts different helix motion tendencies (translation, rotation) as the initial conditions of manipulation. These motion tendencies are caused by the forces/torques imparted to the object upon impact, and are generated by changes of momenta of the closing hand preshape at the contact locations. The generalized impact force patterns vary for different hand preshapes, since each preshape closes upon an object with different momenta types. Consequently, the purposive closing of a preshaped hand should be kinematically modeled in such a way that impact force patterns can be naturally deduced from the model and compared to the desired ones so that this preshaped dosing can be optimized according to the impact force pattern it applies to the object at contact. This would generate the optimal initial conditions of manipulation. Our work in this two part article focuses on developing methods of determining, optimally, the preshape of a robot hand closing onto an object, in order to achieve at contact a certain stability and manipulability degree based on kinematic considerations. Toward this objective, in Part I of the manuscript we define the stability and manipulability criteria of a robot hand preshape based on vortex theory, dealing with the analysis of vorticities in the robot hand workspace. (C) 2000 John Wiley & Sons, Inc.