by Michael Adler
No one who has seen a modern robot at work can fail to be impressed by these modern marvels of technology. For the Meccanoman who is always on the lookout for a new model, especially if he is interested in computer control, the field of robotics and automation can offer rich rewards.
It may be daunting to attempt to reproduce the actions of one of these machines, and the problem of coping with rapidly moving pieces of equipment in multiple planes simultaneously. To add to this, such machines must also interface with a factory environment, where other factors such as conveyors and even fellow robots may be working in unison, each action precisely timed to fit in with the overall scheme of things.
The technology of robotics offers unparalled interest and challenge to the Meccanoman who is involved in small scale engineering. There is no field of robotics and flexible manufacturing or automation that cannot be represented using the Meccano system, which is in fact the perfect medium for building some extremely interesting structures and machines. He is at a distinct advantage because of his ready access to wide range of preformed parts, and the means therefore to rapidly evolve a pieceof machinery which otherwise would require complex manufacture.
Models are often constructed in the real world as a type of breadboarding, to demonstrate the feasibility of a particular idea or system. This obviates excessive capital expenditure, and allows experimentation, and easy alteration of structure and function.
A small robot built from Meccano in no way differs in function from its larger counterpart. The size may be different, but the electronics and control software are exactly the same. As will be shown, there are a number of interesting robot configurations, and at their simplest level they could be controlled by a simple system of on/off switches. The Meccanoman however, who has a simple computer or programmable logic controller, will be able to automate the entire operation, and will thus enter a new sphere of interest for himself, with a new awareness of the modern manufacturing process. For the world of automation means computer integrated manufacturing (C.I.M):
* Parts must be designed specifically to ease the manufacturing process. This means minimal handling, minimal manufacturing steps, ease of storage, ease of orientation for placement in machines and in storage, and ease of mating with fellow components. All this is an art in itself, and a fascinating study.
* The means to store and retrieve parts and devices, in fact automated storage and retrieval (a wonderful subject for a computer controlled model).
* Movements of parts and components to and from the manufacturing process and storage (why not computer controlled conveyers?).
* Automated machines (computer numerical control) and robotic interfacing for manufacture where needed.
All of this brings decided cost advantages. There is a marked reduction of wastage, as there is a sumultaneous improvement in the quality of products. The machines can work continuously, and there can be reduced inventories and stocks.
The name 'robot' is derived from the Czech term 'robota' meaning drudgery or work performed in servitude to a master. Its use to characterise modern robots is the result of a 1927 play by Karl Capeck titled 'R.U.R.' or Russum's Universal Robots. The first robot as we know it today was built in the United States by Unimation for the General Motors c\Company in 1961. There has been an explosive increase in their use since that time.
A robot is a Reprogrammable Multi-functional Manipulator designed to move material, parts, tools or specialized devices through variable programmeable motion for the performance of a variety of tasks. Basically a robot is a device with a single arm for manipulating tools or parts through a programmed sequence of motions through space.
Reprogrammable control is through a controller (on the desk or on the machine) which is usually a computer with memory and a program. The controller is programmed to send signals to the various motors which control movements, and to respond to various sensory devices, which can be impulse or revolution counters, limit switches, angular measurement devices, optical encoders and the like. Each specific action can therefore be accurately reproduced, and can even be easily altered to take into account subtle changes of design or size. The robot must be taught these sequence of movements, and this can even be achieved off the factory floor in computer simulations of the entire manufacturing process.
All robots therefore consist of three main elements:
A Manipulator - the basic mechanical unit responsible for performing the work
A Controller and program - responsible for directing the movements of the manipulator.
A power supply - the energy source for the manipulator and its controller
Below is a simple industrial pick and place robot.
A simple robot is now shown which can easily be built from standard Meccano parts. It is not complicated in its construction. It has two degrees of freedom: Base rotation, an up/down movement of the vertical arm, and an electromagnet (which is really the effector or hand). The Robot has been designed to carry out a specific set of instructions, which will allow it to perform the Tower of Hanoi game. In this game, a stack of three different sized metal discs, with the largest at the bottom and the smallest on top is transfered one by one to another position. At no time is a larger disc to be placed on a smaller disc. The robot can rotated to only three positions. Its starting stack position, a final position where the stack must finally rest , and an intermediate position. The discs are moved one by one. The whole process is controlled automatically by the computer. The program is not complicated, and the means to carry this out is well within the capability of the Meccano robot.
As the robot has two movements, it requires two motors, one for rotation, and the other to move the arm up and down. It also requires a simple electro-magnet powerful enough to lift individual discs.
The Meccano robot shown here is simple to construct, and easy to instrument. The robot of course must also have a few sensors as follows: a potentiometer to sense base rotation. This signal must be converted to a digital signal in order for the computer to understand the degree of rotation in digital terms. It must have a limit switch at each end of the vertical arm motion. The lower of these can be built into the 'hand' so that when the arm is lowered and the electromagnet hits a disc, the limit switch is simultaneously closed thus stopping the motor. Finally, the electro-magnet must itself be controlled. The whole sequence of operations to solve the Tower of Hanoi must be 'taught' to the controlling computer.
No ModelPlans are available for this machine, but its construction is simple. there is a base motor for rotation, with a potentiometer on the central shaft. The vertical arm is moved by a motor mounted inside the horizontal body. A pinion meshes with a vertical rack strip mounted on the arm, which moves on guides. There is a limit switch to sense when the arm is in the upper position, and a lower limit switch mounted just above the electro-magnet.
It is suggested that such a Meccano model could be used for simple first experiments with a standardised Meccano controller.
Michael Adler - May 1999
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