Md4 Chp8 Q18

A robot performs a loading and unloading operation for a machine tool. a double gripper is used instead of a single gripper. The work cycle consists of the following sequence of activities:

Seq. Activity Time

1 Robot reaches and picks raw part from incoming conveyor in one gripper and awaits completion of machining cycle. This activity is performed simultaneously with machining cycle. 3.0 sec

2 At completion of previous machining cycle, robot reaches in, retrieves finished part from machine, loads raw part into fixture, and moves a safe distance from machine. 4.0 sec

3 Machining cycle (automatic) 30.0 sec

4 Robot moves to outgoing conveyor and deposits part. This activity is performed simultaneously with machining cycle. 2.5 sec

5 Robot moves back to pickup position. This activity is performed simultaneously with machining cycle. 1.5 sec

The activities are performed sequentially as listed. Every 20 work parts, the cutting tools in the machine must be changed. This irregular cycle takes 2.0 min to accomplish. The uptime efficiency of the robot is 96%; and the uptime efficiency of the machine tool is 97%, not including interruptions for tool changes. These two efficiencies are assumed not to overlap (i.e., if the robot breaks down, the cell will cease to operate, so the machine tool will not have the opportunity to break down, and vice versa). Downtime results from electrical and mechanical malfunctions of the robot, machine tool, and fixture. Steps 1, 4, and 5 are performed simultaneously with the automatic machining cycle. Steps 2 and 3 must be performed sequentially. The same tool change statistics and uptime efficiencies are applicable. Determine the hourly production rate when the double gripper is used, taking into account the lost time due to tool changes and the uptime efficiency.