The electron-source array of the present invention is provided with cathode electrodes placed on an insulation substrate in the form of lines; and gate electrodes that are placed face to face with the cathode electrodes with the insulation film being interpolated in between. The modular spring assembly may be positioned coaxially with a pivot axis of the folding tool and interconnected to the folding tool. Both surfaces of the driver bodies and the proof masses respectively include a number of grooves respectively perpendicular to a first axis and a second axis.