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It is possible to add sensors to the robot servos so that the final position of the END EFFECTOR is where the sensors command after a staging position which the program commands. I call such systems "active homing guidance."
Typical sensors are limit switches and proximity sensors (optical, acoustic, inductive, capacitive, pneumatic) and in some cases, television.
For the ultimate in precision positioning it is possible to make the end effector "permissive" or "compliant" so that forces on the part or its gripper displace moveable portions of the end effector assembly to permit self alignment. In many cases there is no final error whatsoever, the gripper is truly positioned where it should be, plus or minus zero. I call such action "passive homing guidance." In this case, open loop mechanisms out-perform closed loop servos. Heresy!
Examples of passive homing guidance are described and illustrated in Chapter 14 of my book, "Designing Cost-Efficient Mechanisms."
Homing guidance makes the difference between many successful robots and impossibility.
An early concept in robot development is programming by "teaching" the robot, another anthropomorphic word. The robot is equipped with a switch or other transducer assembly near its end effector. (Sometimes teach switches are separately supported at the end of a flexible cable.) The switch assembly is held by the programming person and moved along the desired motion path while the transducer outputs control the robot motors to follow the transducer assembly. The control computer records the electrical signals generated by the feedback transducers and then regenerates the motion commands.
An application of robots where teach mode is indispensable is spray painting. No one can mathematically define the path of a spray nozzle to produce a finish on a refrigerator door without runs or streaks. However a skilled human in grungy overalls and no great power of verbal articulation can move the nozzle to produce perfect results. The solution is to give this human a real nozzle connected to a set of transducers and ask him to paint a real part by hand. Once. The nozzle is then transferred to the robot which reproduces every flick and twist and sweep of the human painter's hand.
One of the hype fantasies was that a robot, being similar to a human, could be easily reassigned from one job to another merely by moving it across the factory floor and plugging in a new program, just as a human is reassigned to a new task and given a new instruction. This conceit is not just an exaggeration, it is flat out not so. Why not?
The first reason concerns tooling. You and I have standard tooling called hands and fingers, eyes and touch as transducers, brains as controllers, hundreds of muscles as actuators, and tens of joints as axes. Not only can these tools of ours do remarkable feats of dexterity but they can-and often must- pick up and use extension tools like pliers and scalpels.
Robot tools are primitive in comparison and therefore must be made to suit each particular task. (Yes, there are always fatuous R&D; efforts to emulate the human hand. Lots of luck from a very experienced robot tool inventor and designer.) Robot controls are primitive in comparison with human controls and robot articulation (axes and actuators) is a tiny fraction of human articulation.
The second reason is installation. The machines, conveyors, part magazines, etc. working with the robot must be arrayed in a pattern within which the robot can successfully reach and work. The robot must be accurately positioned within that pattern; it does not have eyes and a brain to adapt to it. Guards and interlocks must be provided to prevent a sudden machine defect from causing mechanical damage or human injury. A master programmer must control both the robot and the associated devices. Often the robot's own programmer is in the bottom layer of a hierarchy of controllers. In short, the robot task itself requires extensive engineering aside from the robot itself.
I know of no such multiple purpose robot usage.
Robots can be re-programmed easily for variations within task (e.g. spot welding different chassis); but they can not be converted from task to task except as a long term change with a corresponding investment.
Some robots are cost-justified solely on labor savings, some are cost-justified, at least in part, by the superior uniformity of machine work over human work, and some are cost justified by the savings (and other benefits) in not exposing people to dangerous working conditions. The cost of a robot is approximately the workman's compensation cost of an industrial accident, and there is no assurance that there will not be another accident to the replacement worker.
I have read a lot about robots which "improve the quality of life" in factories, but in all my experience I never met a manager with much of a budget to "improve the quality of life" except as a means to improve profits or to conform to law or union pressure.
Please excuse the cold blooded but realistic language.
The real economic significance of the robot is that the robot itself is a multiple purpose smart machine, produced in quantity, and therefore more cost efficient than a special machine developed to do each kind of job.
I'm sorry you will not get a robot to do your housework. Housework is boring and far below your human capability but it is vastly too complex for any smart machine. Automatic, single purpose machines, like dishwashers, you already have and you can count on more and better as time goes by, but a housework robot? No.
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