Manipulators – Part 5 of 8 Articles
The Programmable Manipulator
Many present-day manipulators now use variable frequency drives with “soft limits”. Endpoints for each path are “taught”. Hard stops are still recommended for these manipulators in order to avoid equipment damage in the event an over-travel condition occurs.
With the capability and cost-effectiveness of present-day control systems, simple X-Y manipulators can be provided with “memories” to allow for a variety of motion programs to be stored and called-up as needed.
| The Programmable Manipulator by Plasma Powder and Systems, Inc. Two points are important regarding programmable manipulators for coating operations. First, by implication, programmable manipulators are generally used in applications where a variety of parts are to be coated. A manipulator dedicated to the coating of a single part is usually not programmable. Second, programmable manipulators for coating operations are a special breed of the manipulator. Palletizing and similar material handling manipulators are designed to move between specific points with an only secondary interest in the speed and path followed. Coating manipulators are designed to follow specific paths with precise speed control. The end-points are only of secondary interest. Programmable manipulators can be as simple as a single axis gun position controller interfaced with a lathe or turntable. The Plasma Powders Landing Gear Spray System is an example of a single axis manipulator. However, manipulation systems can be as complex as a pair of multiple axes robots: one handling the gun and the other handling the part being coated. Originally, single or double axis (X-Y or horizontal/vertical) manipulators used DC motors and trips or limit switches. Programming consisted of setting limit switch positions and the speed of the drive. Many present-day manipulators now use variable frequency drives with “soft limits”. Endpoints for each path are “taught”. Hard stops are still recommended for these manipulators in order to avoid equipment damage in the event an over-travel condition occurs. With the capability and cost-effectiveness of present-day control systems, simple X-Y manipulators can be provided with “memories” to allow for a variety of motion programs to be stored and called-up as needed. X-Y Programmable Manipulators can be based on brushless variable frequency AC motors with servo-drives and Programmable Logic Controllers (PLCs). The PLC can also serve as the “Master” over the thermal spray system. PLC based X-Y manipulators can include the following features and functions: A handheld teach-pendant for programming the controller at the manipulator. Keys or a “Joy Stick” to jog each axis of the manipulator through the desired program path. Operator adjustable jog speeds. Programming capability to “teach” each position of the gun during the execution of the program. Points are “taught” by jogging the manipulator to each program point and then pressing a “teach” key. Capability to step through a program and touch-up each position as necessary for the program. Capability to program the speed of motion of each segment when traversing between points. Ability to define a “Park” position of traversing between points.Ability to define a “Park” position of the gun for loading and unloading the parts to be coated.Ability to define a “Gun Light/Shutdown” position. Digital output signals to start and stop the thermal spray controller, the powder feeder, the turntable and the dust collection system. Digital inputs to recognize that the gun is operating, the powder feed is on, the turntable is operating (a zero-speed sensor) and the dust collection system is operating. Facility to identify each program, save it and recall it from the “teach” pendant. The means to back up the program on a memory unit. The next and sixth article in the series regards “The Thermal Spray Robot”. |