Question 3.CS.5B: Fourbar Linkage Dynamic Loading Measurement Problem: Determi...
Fourbar Linkage Dynamic Loading Measurement
Problem: Determine the actual forces acting on the fixed pivots of the fourbar linkage in Figure 3-11 (p. 99) during one revolution of the input crank.
Given: The linkage is driven at 60 rpm by a speed-controlled electric motor, and force transducers are placed between the fixed pivot bearings and the ground plane.
Assumptions: There are no applied external loads on the system; all loads are due to the accelerations of the links. The weight forces are insignificant compared to the inertial forces and will be neglected. The force transducers measure only dynamic forces.
See Figures 3-12 (p. 99) and 3-16 (p. 106).
1 Figure 3-11 shows the fourbar linkage. It consists of three moving elements (links 2, 3, and 4) plus the frame or ground link (1). The shock-mounted motor drives link 2 through a gearbox and shaft coupling. The two fixed pivots are instrumented with piezoelectric force transducers to measure the dynamic forces acting in x and y directions on the ground plane.
2 Figure 3-16 shows an actual force and torque measured while the linkage was running at 60 rpm and compares them to the theoretical force and torque predicted by equations a–d in Case Study 5A.^{[5]} Only the x component of force at the pivot between link 2 and the ground and the torque on link 2 are shown as examples. The other pin forces and components show similar deviations from their predicted theoretical values. Some of these deviations are due to variations in instantaneous angular velocity of the drive motor. The theoretical analysis assumes constant input shaft velocity. Vibrations and impacts account for other deviations.
