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Pneumatic Drive






Pneumatic drive systems make use of air-driven actuators. Since air is also a fluid, many of the same principles that apply to hydraulic systems are applicable to pneumatic systems. Pneumatic and hydraulic motors and cylinders are very similar. Since most industrial plants have a compressed air system running throughout assembly areas, air is an economical and readily available energy source. This makes the installation of robots that use pneumatic actuator drives easier and less costly than that of hydraulic robots. For lightweight pick-and-place applications that require both speed and accuracy, a pneumatic robot is potentially a good choice.

Pneumatic actuator drives work at high speeds and are most useful for small-to-medium loads. They are economical to operate and maintain and can be used in explosive atmospheres. However, since air is compressible, precise placement and positioning require additional components to achieve the smooth control possible with a hydraulic system. These components are discussed in later chapters. It is also difficult to keep the air as clean and dry as the control system requires. Robots that use pneumatic actuator drives are noisy and vibrate as the air cylinders and motors stop.

Shape of the Work Envelope

Robots come in many sizes and shapes. The type of coordinate system used by the manipulator also varies. The type of coordinate system, the arrangement of joints, and the length of the manipulator’s segments all help determine the shape of the work envelope. To identify the maximum work area, a point on the robot’s wrist is used, rather than the tip of the gripper or the end of the tool bit. Therefore, the work envelope is slightly larger when the tip of the tool is considered.

Work envelopes vary from one manufacturer to another, depending on the exact design of the manipulator arm. Combining different configurations in a single robot can result in another set of possible work envelopes.

Before choosing a particular robot configuration, the application must be studied carefully to determine the precise work envelope requirements.

Some work envelopes have a geometric shape; others are irregular. One method of classifying a robot is by the configuration of its work envelope.

Some robots may be equipped for more than one configuration. The four major configurations are: revolute, Cartesian, cylindrical, and spherical. Each configuration is used for specific applications.

Revolute Configuration (Articulated)

The revolute configuration, or jointed-arm, is the most common. These robots are often referred to as anthropomorphic because their movements closely resemble those of the human body. Rigid segments resemble the human forearm and upper arm. Various joints mimic the action of the wrist, elbow, and shoulder. A joint called the sweep represents the waist.

A revolute coordinate robot performs in an irregularly shaped work envelope. There are two basic revolute configurations: vertically articulated and horizontally articulated.

The jointed-arm, vertically articulated robot is useful for painting applications because of the long reach this configuration allows.

The horizontally articulated configuration generally has one vertical (linear) and two revolute joints. Also called the SCARA (selective compliance assembly robot arm) configuration, it was designed by Professor Makino of Yamanashi University, Japan. The primary objective was a configuration that would be fairly yielding in horizontal motions and rather rigid in vertical motions. The basic SCARA configuration is an adaptation of the cylindrical configuration.

SCARA robots are ideally suit ed for operations in which the vertical motion requirements are small compared to the horizontal motion requirements. Such an application would be assembly work where parts are picked up from a parts holder and moved along a nearly horizontal path to the unit being assembled.

The revolute configuration has several advantages. It is, by far, the most versatile configuration and provides a larger work envelope than the Cartesian, cylindrical, or spherical configurations. It also offers a more flexible reach than the other configurations, making it ideally suited to welding and spray painting operations.

However, there are also disadvantages to the revolute configuration. It requires a very sophisticated controller, and programming is more complex than for the other three configurations. Different locations in the work envelope can affect accuracy, load-carrying capacity, dynamics, and the robot’s ability to repeat a movement accurately. This configuration also becomes less stable as the arm approaches its maximum reach.

Typical applications of revolute configurations include the following:

• Automatic assembly

• Parts and material handling

• Multiple-point light machining operations

• In-process inspection

• Palletizing

• Machine loading and unloading

• Machine vision

• Material cutting

• Material removal

• Thermal coating

• Paint and adhesive application

• Welding

• Die casting


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