Automatic Pendulum Return
Pendulum impact tests require latching of the pendulum at the desired release angle (typically 135 degrees). For large capacity test machines (100 ft-lbs to 300 ft-lbs), this operation requires considerable strength to raise the hammer above eye level. After the impact event, it is common practice in some laboratories to step into the swing path to catch the hammer on the return swing and manually return it to the latch position. This practice is dangerous and can result in serious injury. While the danger is less with smaller capacity tabletop machines, there are cases, such as in nuclear hot cell testing, where it is not possible to have access to the test machine for manual operations. In these situations and with the larger capacity test machines (400 ft-lbs to 700 ft-lbs), the automatic hammer return system is a necessity.
The MPM hammer return system hardware consists of a clutch, brake, and motor. The system is interfaced with an optical encoder that is mounted on the bearing shaft to continuously monitor the angle of the pendulum. The motor may be applied at any time to raise the hammer to any desired latch position. During a routine test, the hammer is released, and at the optimum position on the back swing, the system initiates the clutch and the motor is applied to return the pendulum to the latch position. The hammer release and brake are controlled by a console switch and/or the ImpactTM v4.3 software. An important safety feature of the system is that electrical power must be present for the hammer to swing, an inherent fail safe design. Further, the test machine enclosure door is interlocked so that it is impossible to release the hammer when the door is open. This safety feature is very important in most applications, particularly in student laboratories or factory floor settings where untrained personnel are present.