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SYSTEM DESIGN AND INTEGRATION FOR REPEATED IMPACT TESTS

Abstract

The design and integration of an impact-testing machine is particularly for the test of an object which is repeatedly dropped down from a specified height. Four linear actuators with two on each of the two magnetic rails are used to lift up an object weighing up to70 lbs. Each actuator is powered and controlled by an industrial amplifier. A Programmable Logical Controller (PLC) is applied to activate these four actuators simultaneously and repeatedly. Accelerometers using an National Instruments (NI) data acquisition system are used to measure the impact force during the tests. Students gain design and implementation experiences from the developing of the system.

1. Introduction A collision between two bodies which occur in a very small interval of time, and during which the two bodies exert on each other relatively large forces, is called an impact1. The following impact-force equation can be used to illustrate the physical situation.

(1) Where F represents the impact force; m represents the mass of the object; m is the mass of the object; ∆V represents the velocity change between the initial velocity and the velocity after impact; ∆t represents the impact time, which is very small when impact occurs. During the impact, the struck object behaves as if it were more brittle than it is, and the majority of the applied force goes into fracturing the object. As illustrated in Equation (1), impact force can be greatly reduced when ∆t increases. This can be achieved through the design of a soft contact during the impact. A machine which can create impact motions is needed to test the performance of the impact absorbing device. The design for this machine is to provide an impact-testing facility for either biomechanical devices or electronic equipment when operated in the repeated impact environment, which may include a boat on various sea state motions2, electronic equipment on a boat3, and nailing task motion4, etc. The system can be applied to perform the test of the equipment when operated in such a dynamic environment, and also to evaluate impact-absorption devices. The impact force is measured through the use of accelerometers. The whole system includes mechanical design, electrical control, PLC programming, and data acquisition for accelerometers.

2. Mechanical Design Figure 1 shows the mechanical design of the system. To lift up the object, the servo-control ThrusTube5 motors from Copley Controls Corp. are used as linear actuators or motors, which have excellent performances on high speed and acceleration, reliability and controllability, and

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Lin, C., & Hou, G., & Bawab, S., & Coats, T., & Nassar, H. (2009, June), System Design And Integration For Repeated Impact Tests Paper presented at 2009 Annual Conference & Exposition, Austin, Texas. 10.18260/1-2--4957