1.3.1 Overview
• Unlike many machines, robots are easy to imagine performing tasks, because of their similarity to the human form. This has caused many companies to adopt robots without properly assessing what their strengths and weaknesses are.
• The early days of experimentation lead to many failed applications, as well as some notable successes.
• A useful dichotomy is,
Point-to-Point - A robot that typically only has 2 (or very few) possible positions. These are good for pick and place type operations, and they are often constructed with pneumatic cylinders.
Manipulation - A robot that assembles, or moves parts requires good end of path motion, but does not require as much accuracy in the middle of the path. A higher speed between path endpoints is often desired.
Path Tracking - When arc welding, gluing, etc. the robot must follow a path with high accuracy, and constant speed. This often results in slower motion, and more sophisticated control software.
Operating - The robot will be expected to apply forces to perform work at the end of the tool, such as doing press fits. While the demands for these robots is essentially the same, they must be capable of handling the higher forces required when in working contact with the work.
Telerobotics - Acts as a remote extension of human control, often for safety or miniaturization purposes. In these cases the robots often mimic the human form, and provide some forms of physical feedback.
Services - mail delivery, vacuuming, etc.
Biomedical - prosthetic and orthotic devices.
• The number of degrees of freedom of the robot should be matched to the tasks.
• Note: 5 d.o.f. robots will allow the tool to reach all points in space if the tool has an axis of symmetry. For example, a welding torch flame has a symmetrical axis.
• Some commercial applications that have been done with robots are,
- die casting - used for unloading parts from dies, quenching parts, and trimming them with a trim press. The robot may also be used to put inserts into the die.
- spot welding - spot welding electrodes are clamped in place, and the weld is made. The robot allows many welds to be done.
- arc welding- continuous path robots are used to slowly track a path with a continuous rate, and with control of welding parameters.
- investment casting - robots can be used in the pick and place operations involved in making the molds.
- forging- a robot can be used to precisely position the work under the impact hammer, freeing a worker from the handling hot heavy work pieces.
- press work- the robot handles loading parts into the press, and removing the resulting work pieces.
- spray painting- a very popular application in which the robot sweeps the paint head across the surface to deposit a spray. This process has been coupled with electrostatics to improve efficiency and distribution.
- plastic molding - they can be used for loading the hoppers, and unloading the parts. This is most effective when the parts are hard to handle.
- foundry process- robots can be used for ladling materials, and preparation of molds.
- machine tools- robots can be used for loading and unloading machine tools, and material transfer systems.
- heat treatment process - parts can be loaded into the ovens, unloaded from the ovens, quenched and dried by robots.
- metal deburring - continuous path robots can be used to track rough edges with a compliant tool design.
- palletizing process - parts can be placed in boxes, or on skids in preparation for shipping. Most robots have program commands to support this.
- brick manufacture - a robot can be used for loading and unloading a kiln, and stacking bricks for shipping.
- glass manufacture - a robot can handle the breakable glass with a wide EOAT that prevents sagging, etc. The robot can also be used for grinding edges.
1.3.2 Spray Painting and Finishing
• Air spraying - air under pressure causes the paint to atomize and be propelled to the article to be painted
• Airless spraying - finishing materials, such as paint, are sprayed under considerable hydraulic pressure through a fixed orifice, which causes the paint to be atomized directly without the need for air.
• Electrostatic spraying - Atomized particles (paint or powder droplets) are electrostatically charged. These are attracted to the object being sprayed by the applied electrostatic field. Considerable material savings are achieved since very little of the sprayed material bypasses the object and is lost. Objects being sprayed are kept at a ground potential to achieve a large electrostatic field.
• Heating of materials - paint decreases in viscosity when heated and can be sprayed with lower pressures. Less solvent is required and there is less overspray of paint. Heating may be used with any of the preceding systems
• Air spraying and electrostatic spraying are the most common methods of application for paints, enamels, powders, and sound absorbing coatings.
1.3.5 Belt Based Material Transfer
• When a robot is used in a workcell, the raw part is delivered in, worked on, and then moved out. This can be done using moving belts, etc.
• Parts are placed directly on the belt, or placed on pallets first.
• Belts can travel in straight paths, or in curved paths if flexible belt link designs are used.
• If straight belts are used, transfer points can be used at the end to change part/pallet direction
• When pallets are used, there is a fixture on top designed to hold the part in an accurate position so that robots and other equipment will be able to locate the part within some tolerance.
• Vision systems may be necessary if part orientation cannot be fixed.