Many manipulator configurations have been used in thermal spray. Plasma Powders & Systems, Inc. offers an eight-part series of articles about manipulators, taking an in-depth look at the manipulation systems and applications used in the thermal spray industry. Which manipulation system is best for your shop or specific application?
These articles are primarily oriented towards management to highlight issues that need to be considered. The information should also be of value to the thermal spray technician and the manipulator programmer when considering options for setting up and operating a manipulator.
The first manipulator article, titled “Taking Notice of the Manipulator”, considers the question “why automate the application process?” The first objective is usually cost reduction, but there are other concerns to take into account.
Which manipulation system is best for your shop or specific application? Manipulation involves motion control and positioning. Many manipulator configurations have been used in thermal spray. A thermal spray manipulation “system” can be as simple as a fixed-speed turntable or as complex as two robots working together for the coating process: one holding the part and the other the gun.
What manipulator systems are available and what are the pros and cons of each? As with many technical specialties, the robotics industry has their own terminology. We review those terms.
Before choosing a manipulator, we need to fully understand what is expected of it. How will it add to productivity? What is its purpose?
Will the manipulator control the gun, the work piece or both? In the majority of thermal spray applications, the manipulator controls the gun. The piece being sprayed is fixed, mounted to a turntable or mounted to a lathe. The primary question is where will the system fit within the production operation?
Manipulator qualifications fall into three categories: fixed, controllable and programmable. When choosing a manipulator, make certain it is the correct choice for the job.
An overqualified manipulator may lead to unnecessarily high costs with respect to training, operation and maintenance or demand special skills for programming, operation and maintenance. In addition, an overqualified manipulator may be faced with early obsolescence
Many present day manipulators now use variable frequency drives with “soft limits”. End points 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.
Robots used for thermal spray operations are typically of the articulated style with either five or six axes, six being preferable for flexibility. The articulated robot employs rotary joints for motion and functions much like a human arm. In fact, human anatomy terms, such as wrist and arm, are often used to describe robotic operations.
A key to the success of the articulated robot is the advanced controller software. Thermal spray operators are generally most comfortable with X-Y-Z manipulators as it is difficult to visualize a position based on the angular position of six rotary joints. The advanced robot software addresses this transformation and allows the programmer/ operator to calculate in Cartesian coordinates.
Robot paths, not end points, are key for thermal spray operations. In some point-to-point robotic operations (such as in palletizing), the robot may pause at each end-point in the path. This is unacceptable for many thermal spray operations; therefore, the continuous path is used. The path is continuously and smoothly controlled by the coordinated motion of the robot joints.
In this final article in our series on manipulators, we will cover the mounting of the gun on an articulated robot and the safety of robotic operations. Some thermal spray operations may mount the gun in line with the last axis of the robot. While this may be the simplest approach, it is one of the least desirable. With the gun in line with an axis of the robot, the benefit of that axis is essentially lost. Rotation of the gun about its axis has little benefit. Also, mounting the gun straight out from the last axis results in the gun being cantilevered out from the robot, placing unnecessary loads on the robot.