A method and apparatus for impacting a surface with a desired kinetic impact energy wherein an impacting device which can apply a variable impact energy corresponding to the magnitude of an input control signal is provided and placed adjacent the surface to be impacted. Thereafter, an input control signal of a preset magnitude is applied to the impact device to initiate an impact, the kinetic energy of the impact is determined, the value of the determined kinetic energy is compared with a value corresponding to the desired kinetic impact energy, the results of the comparison are indicated, the preset magnitude of the signal used for the control signal is adjusted to reduce any difference noted as a result of the comparison, and the process is repeated until a repeatable impact of the desired impact energy is determined and indicated. Preferably, the impacting device is a solenoid whose plunger provides the impact, the input control signal is an input voltage applied across the solenoid coil, and the impact energy is determined by measuring the velocity of the plunger just prior to impact by: sampling the magnitude of a signal, whose magnitude is proportional to the distance moved by said plunger, at uniform time increments; subtracting the sampled values from successive sampling times to provide difference values; and, upon detecting a zero difference value, indicating that impact has occurred, utilizing the immediately previously provided difference value as a measure of the velocity of the plunger just prior to impact, and thus of the kinetic impact energy.
