A clamping apparatus includes a housing and a pivot pin mounted for pivoting movement about an axis of rotation with respect to the housing. A clamp member is connected to the pivot pin and is moveable between a clamped position and a released position in response to rotation of the pivot pin. The pivot pin has an arm extending radially outwardly from the axis of rotation. A drive member is mounted for linear reciprocal movement along a fixed path with respect to the housing, and a linkage connects the drive member to the arm of the pivot pin for converting reciprocal movement of the drive member into pivoting movement of the pivot pin. An electric motor is connected to an output shaft with an axis of rotation, and an adjustable converting mechanism connects the drive member to the electric motor for adjustably converting the rotary motion driving force into a linear reciprocal harmonic motion of the drive member. The adjustable converting mechanism allows the stroke of the linear reciprocal motion to be adjusted. In addition, an automatic adjusting mechanism allows the drive member to adjust its length in response to the driving force of the electric motor and the position of the clamp member.