Types of Robots

There are various types of robots in use in laboratories, some being better suited for a particular application than others. The primary types of robots used in today's laboratories are of the ''articulated arm'' and ''cylindrical coordinate'' style.

1. Articulated Arm Robots

Articulated arm robots are characterized by an arm with a bending joint in the middle, sometimes referred to as the ''elbow'' joint, with the obvious anthropomorphic reference to the human arm. This type of jointed arm allows the robot to work close to its base and also reach out to the furthest extent of the working range. Articulated arm robots typically have five axes, excluding the track that the robot may be mounted to. Typically there are three major axes, including a base swivel (the ORCA does not have a base swivel but can move the arm over the base to access both sides of the track), a shoulder, and elbow axes. There are typically two wrist axes. The roll axis moves the gripper or ''hand'' around the axis perpendicular to the gripper mounting plate (also sometimes called the ''tool'' mounting plate). The fifth axis is an angular axis and is called ''pitch'' when it is oriented to move the tool up and down, and ''yaw'' when it moves the tool from side to side. Some models of laboratory robots have both pitch and yaw axes and thus have six axes. (The linear track is usually termed an auxiliary axis and is rarely counted as one of the main robot axes). Typical suppliers of articulated arm robots are; CRS Robotics Corp. (Burlington, Ontario, Canada), Beckman Coulter, Inc. (Fullerton, CA), and Mitsubishi Robotics (Japan). A typical articulated arm robot is shown in Figure 3.

Figure 3 Articulated arm robot of the Robocon automation system.

2. Cylindrical Coordinate Robots

Another style of robot commonly used in laboratories is the cylindrical coordinate style, such as the Zymate robot manufactured by Zymark Corp. (Hopkinton, MA). The arm on this style of robot is always horizontal with no joints and moves in simple horizontal and vertical movements in order to reach the programmed point within the work envelop.

The three main axes on the cylindrical coordinate robots include a base swivel, vertical movement of the arm, and horizontal arm movement. Unlike the articulated arm robots that move the elbow joint to fold up or extend the arm, cylindrical coordinate robots have a fixed length horizontal arm. Although these robots have fewer axes and are mechanically simpler than the articulated arm design, the fixed arm length is a disadvantage when considering the usable work envelope. Care must be taken when laying out the work area to assure that there is full clearance so the back of the arm does not hit an object on the other side of the table. The articulated arm style of robot avoids this problem by being able to fold up the arm so objects on the other side of the table are not hit when the base swivels.

This restriction serves to limit the robot's effective work envelope, but the simplicity of this type of robot has greatly contributed to its widespread use. Robot arms usually swivel at the base to allow the arm to move from side to side, allowing the robot arm to reach items on either side of the robotic system. Robots of this type are also oftentimes mounted on a linear track to expand the working range of the robot. Many of the devices used in robotic systems, such as plate storage devices, incubators, instruments, and so forth can be installed on either side of the track, which allows the robot working volume to be used more effectively.

3. Overhead Gantry Robots

Another style of robot is the overhead gantry. This design has a carriage that moves above the work surface, usually supported by a structure on one or more sides, depending on the weight and size of the carriage and overhead frame. From the carriage, the tools are raised or lowered as required. This vertical axis is sometimes referred to as the ''Z'' axis. The overhead robot uses linear rather than jointed or rotational axes, which makes the mechanical unit simpler than the articulated arm and cylindrical coordinate robot style.

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