No abstract

Mechanical, potentiometric, and photoelectric indicators have been used to study hand-operated impact machines. The angular velocity and torque are determined oscillographically by means of sensitive generators and elastic potentiometer devices [1,2,3,4,5]. The joint use of these methods involves the adjustment of complex electrical circuits, which is time-consuming. This article describes the use of high-speed cinematography to study the dynamics of an electromechanical hammer. This method requires much less time than the others, and is simpler in experimental technique.The electromechanical hammer studied is a hand tool in which the rotation of the armature of an electric motor is converted to reciprocating motion by means of two disc-shaped cams, arranged symmetrically about the hammerhead's axis and with working contours on their inner surfaces [6]. In action, the motor turns the cams, whose contours run on rollers in the head and raise it, compressing the drive spring. The head then breaks away and delivers the blow. After recoil and shock-absorption the cycle is repeated.The presence in the kinematic chain of the hammer mechanism of a spring, which plays the part of a semirigid link, means that there is an unknown recoil, Krec; furthermore, our inadequate knowledge of the practical friction conditions required us to compare the theoretical behavior of the mechanism with its actual behavior. To measure the latter we used a high-speed cine-camera.The films were taken as follows. A slot was made in the hammer frame for observation of the spring coils and head, and an indicating device was fixed on the drive shaft to register the torque (Fig. 1). Its mechanical base was borrowed from a potentiometric torque transducer [2]. It consists of two discs joined by a cylindrical helical spring which acts as a torsion shaft. This is fixed between the drive shaft and the driven shaft. According to the torque magnitude, the spring becomes twisted to a greater or lesser extent, its angular displacement being imparted to the discs. The angle can be read off from the relative positions of graduations painted in white on the edgesofthe discs.The films were recorded at 800 frames/sec on 16-mm film by means of an SKS-1 camera of Soviet manufacture. The frame frequency was determined from the trace of a neon time indicator. Illumination was by a lamp projector giving 15000 lux at the object. The film was of type DK. Measurements on the film were made with a microscope of type ChP (clockwork projector).The use of high-speed cinematography enabled us to solve the entire complex problem. A single film yielded the time-dependence of several variables characterizing the action of the mechanism-the displacement of the head and spring coils, the angular velocity of the shaft, and the torque and the work and power expended by it.The displacement of the indicator discs gives the indicated torque, which is proportional to it since the indicator spring is within its elastic limit. In the process under examination, the torque and angular ve...