Stationary Robots

Part I: Types of Robot Joints

Stationary robots are not mobile, and they perform their tasks at a fixed location. Six main types, cartesian, cylindrical, spherical, SCARA, articulated, and parallel, are commonly used at machine shops. Each type has a different joint configuration.

These robots handle objects by controlling the position and orientation of an end-effector, such as a welding, drilling, or gripping apparatus.

Cartesian (Gantry) Robots

Cartesian are also called gantry or rectilinear robots. They have the advantage of large work areas and better positioning accuracy. Their three linear joints are operated in line with a Cartesian coordinate system by linear guide rails. Because they work with an X, Y, Z coordinate system, their motion is easier to program. They are also less constrained by floor space. Typical applications include arc welding, assembly operations, pick-and-place applications, sealant application work, and machine tools operations.

Cylindrical Robots

A cylindrical robot typically has three axes of movement, two translational and one rotary. In the given example, the rotary joint uses a twisting motion – one translational joint moves in a linear motion, while the other moves in an orthogonal motion. Cylindrical robots are used for spot welding, assembly work, and machine tools and die-cast machines operations.

Spherical Robots

These are also regarded as polar robots, its arms working within spherical or near-spherical work envelopes. Because it is positioned by a polar coordinate system, it is more complicated to use than Cartesian and cylindrical robots. A robot with an T-L-R structure is illustrated below. Most modern industrial robots are derivatives of this type, and they are used for spot welding, gas and arc welding, assembly work. They can also handle die casting, machine tools, and fettling machines.

SCARA Robots

Scara robot has a ‘shoulder’ and ‘elbow’ joint along with a ‘wrist’ axis and vertical motion. Because its motions are similar to that of a human arm, the robot is primarily used for assembly applications. Typical applications include pick-and-place work, sealant application work, assembly operations, and machine tools operations.

Articulated Robots

An articulated robot may have as many as 10 axes, though four to six are more commonly seen. Because each axis is a different joint, the articulated robot has more degrees of freedom than the above-mentioned robots, making it more versatile and appealing. Such robots are used in applications such as welding, dispensing and material removal, and material handling.

Parallel Robots

Parallel robots are also known as delta robots. They are built from jointed parallelograms that move in a dome-shaped envelope. This averages out the errors in chain positioning. Since the errors of serial robots are cumulative, delta robots are more accurate, making it ideal for pick-and-place operations.

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