Robot Basics

Primarily this site is dedicated to robotic palletizing and robots used in that pursuit.  This page is intended only as the briefest of overviews for our audience to help acquaint them with a few of the terms and concepts that may come in useful during the course of our conversations together.

Scara

Scara robots are well suited for stacking a single pallet where space is limited.  This type of robot has 4 axes of movement, 3 rotational and 1 vertical.  A major "arm" is mounted such that the whole mechanism can move vertically.  This arm is also capable of rotational movement.  Mounted on the major "arm" is a minor "arm", also capable of rotational movement.  At the end of the minor arm is a "wrist", which attaches to the robot gripping mechanism.  The wrist moves in a rotational manner as well, in order to rotate bags or cases for placement.  Scara robots are fast and use little space.  They may not be suited for applications that require multiple loading positions or pickup positions.  Pictured are two examples of Scara robots.

Gantry

Gantry robots come in various shapes and sizes.  Typically when someone refers to a gantry robot, what they really mean is a robot that hangs upside down and travels along either an 'X' or 'X' / 'Y' path to get to its pickup/putdown points.  Pictured above is a Fanuc robot with an 'X' directional gantry travel.  If the beam that the robot is mounted on were also to travel the robot would be capable of 'Y' directional travel as well as 'X'.  This type of configuration is well suited for stacking multiple pallet positions.  So, for instance, a distribution center could have an Order Fullfillment System or OFS that has 20 products that come in as 1 product per pallet.  The DC needs to stack mixed pallets for distribution to their "customer".  Customer in this context could refer to a sales location of the same company.  So, this order fullfillment system could de-palletize product from the "pure" pallets that come in and re-palletize the product into a "mixed" pallet for shipment to the customer.  There could also be any number of "output" positions.

Articulating Arm

The articulating arm robot is perhaps the most widely used and flexible type of robot.  It is capable of a wide range of motion and reach.  While it may not be quite as fast as the Scara type of robot, it can generally do the same type of tasks.  Given the task of palletizing, the Articulating Arm robot is capable of palletizing many pallet positions simultaneously, while the Scara is more limited due to its smaller reach.  A 6 axis Articulating Arm robot can be used for welding, painting, material handling, palletizing and many other types of operations.  A 4 axis Articulating Arm robot has lesser capabilities as far as pickup and placement of materials, but will typically be faster.  6 axis robots of this type are widely used in the Automotive industry, while 4 axis robots are typically used for palletizing operations, where speed is more critical than flexibility.  Shown is a Kawasaki Articulating Arm robot.

Robot Movements

4-Axis

As mentioned above, the 4 axis Articulating Arm robot is mostly used in palletizing and material handling operations.  An "axis" refers to a range of motion.  So, as can be seen in the drawing, the A-1 "joint" is the primary motion center for this robot, as it turns the whole robot around.  Shown is a drawing of a Kuka robot, however, all robot manufacturers have different nomenclature for the various joints.  In the case of Kuka, they call the primary joint A-1, Fanuc calls it J1, but no matter what it is called the speed of this joint is usually the dominant factor in overall robot speed.

As you can see, the A-2 and A-3 joint work in unison to extend the robot outward toward its target.  If you look closely at the picture, you will notice a bar along the top of the robot.  This bar keeps the A-6 joint perpendicular to the floor.  The A-6 joint is where the end effector (or gripper) is mounted.  It rotates so that proper placement of the payload can be achieved.

6-Axis

As with the 4 axis unit above, the A-1 joint is the prime mover.  The A-2 and A-3 joints extend the robot and the A-6 joint rotates the end effector.  Unlike the 4-axis unit, the 6-axis type of robot has an A-4 and A-5 joints.  Although it may seem from the drawing that the A-4 joint works with the A-6 joint for rotational movement, such is not the case, as the A-4 joint has the ability to rotate the A-5 joint as well.  Using the A-4 and A-5 joints, it is possible to pickup a part that is not necessarily parallel to the floor, i.e., ALL range of motion is possible.  That's why this type of robot is so popular with welding, painting and extrusion type applications.  The 6 axis robot is generally more precise in its accuracy to position its end effector than 4 axis models.  It is also usually more expensive than the 4 axis models.

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