Tools

 Tools

The robot uses tools to perform processing operations on the work part. The robot

manipulates the tool relative to a stationary or slowly moving object (e.g., work part

or subassembly). Examples of tools used as end effectors by robots to perform processing applications include spot welding gun, arc welding tool; spray painting gun; rotating

spindle for drilling, routing, grinding, and similar operations; assembly tool (e.g., automatic screwdriver); heating torch; ladle (for metal die casting); and water jet cutting tool.

In each case, the robot must not only control the relative position of the tool with respect

to the work as a function of time, it must also control the operation of the tool. For this

purpose, the robot must be able to transmit control signals to the tool for starting, stopping, and otherwise regulating its actions.

In some applications, the robot may use multiple tools during the work cycle. For

example, several sizes of routing or drilling bits must be applied to the work part. Thus,

the robot must have a means of rapidly changing the tools. The end effector in this case

takes the form of a fast-change tool holder for quickly fastening and unfastening the various tools used during the work cycle.

8.4 Applications of Industrial Robots

Robots are used in a wide field of applications in industry. Most of the current applications are in manufacturing. The applications can usually be classified into one of the

following categories: (1) material handling, (2) processing operations, and (3) assembly

and inspection. Section 8.4.4 lists some of the work characteristics that must be present in

the application to make the installation of a robot technically and economically feasible.

8.4.1 Material Handling Applications

In material handling applications, the robot moves materials or parts from one place to

another. To accomplish the transfer, the robot is equipped with a gripper that must be

designed to handle the specific part or parts to be moved. Included within this application

category are (1) material transfer and (2) machine loading and/or unloading. In many material handling applications, the parts must be presented to the robot in a known position

and orientation. This requires some form of material handling device to deliver the parts

into the work cell in this position and orientation

the robot unloads the finished parts; and (3) machine loading and unloading, which involves

both loading of the raw work part and unloading of the finished part by the robot. Industrial

robot applications of machine loading and/or unloading include the following processes:

• Die casting. The robot unloads parts from the die casting machine. Peripheral operations sometimes performed by the robot include dipping the parts into a water

bath for cooling.

• Plastic molding. Plastic molding is similar to die casting. The robot unloads molded

parts from the injection molding machine.

• Metal machining operations. The robot loads raw blanks into the machine tool and

unloads finished parts from the machine. The change in shape and size of the part

before and after machining often presents a problem in end effector design, and

dual grippers (Section 8.3.1) are often used to deal with this issue.

• Forging. The robot typically loads the raw hot billet into the die, holds it during the

forging strikes, and removes it from the forge hammer. The hammering action and

the risk of damage to the die or end effector are significant technical problems.

• Pressworking. Human operators work at considerable risk in sheetmetal pressworking operations because of the action of the press. Robots are used to substitute for

the workers to reduce the danger. In these applications, the robot loads the blank

into the press, then the stamping operation is performed, and the part falls out of

the machine into a container.

• Heat-treating. These are often relatively simple operations in which the robot loads

and/or unloads parts from a furnace.

8.4.2 Processing Operations

In processing applications, the robot performs some operation on a work part, such as

grinding or spray painting. A distinguishing feature of this category is that the robot is

equipped with some type of tool as its end effector (Section 8.3.2). To perform the process, the robot must manipulate the tool relative to the part. Examples of industrial robot

applications in the processing category include spot welding, arc welding, spray painting,

and various machining and other rotating spindle processes.

Spot Welding. Spot welding is a metal joining process in which two sheet metal

parts are fused together at localized points of contact. Two electrodes squeeze the metal

parts together and then a large electrical current is applied across the contact point to

cause fusion to occur. The electrodes, together with the mechanism that actuates them,

constitute the welding gun in spot welding. Because of its widespread use in the automobile industry for car body fabrication, spot welding represents one of the most common

applications of industrial robots today. The end effector is the spot welding gun used

to pinch the car panels together and perform the resistance welding process. The welding gun used for automobile spot welding is typically heavy. Prior to the application of

robots, human workers performed this operation, and the heavy welding tools were difficult for humans to manipulate accurately. As a consequence, there were many instances

of missed welds, poorly located welds, and other defects, resulting in overall low quality

of the finished product. The use of industrial robots in this application has dramatically

improved the consistency of the welds.

Robots used for spot welding are usually large, with sufficient payload capacity

to wield the heavy welding gun. Five or six axes are generally required to achieve the