Control Applications

2 May

There are many functions encompassed in a modern bespoke automation system. These functions vary greatly and also vary from application to application. In a robot control application the computer provides the following functions:

  • Run the motors (usually 5 or more)
  • Read all the encoders
  • Set the PWM amplifier gain for all motors
  • Monitor the input lines
  • Set the output lines
  • Receive all communications from one or more ports
  • Send information to other machines needing information
  • Monitor the control panel of the robot
  • Update the CRT on the controller
  • Perform all the calculations needed for proper operation
  • Parse the instructions in the program
  • Detect errors in the program lines

As you can imagine a very powerful computer would be required to carry out all of the above functions. Most robot controllers have at least one 32 bit processor for running them. The usual configuration will have at least two microprocessors with one in charge of the motors and other in charge of all of the functions. With the advent of cheaper and specialised microprocessors additional processing units are being used to control various functions in the machine. For example, in a modern robot, the following functions are handled by separate micro-processors.

This means that the main processor tells each of the subordinate processors what they need to do in a special language they both need to understand and then go on to the next one. If the sub-ordinate processors need attention they interrupt the main processor and tell it what they need when they are asked to. Doing it this way makes it much easier to create a fast and responsive system. A modern industrial robot may have as many as 16 32 bit processors. A robot is a state machine and although there are a large number of states, it can assume only a finite number. There in lays the problem with most computer systems.

Robotic Vision Systems

3 Dec

A camera mounted to a robot is not a new concept by any means and the idea was first pondered in the 1950s. When a robot must be controlled by a human operator who is not local to the machine, cameras must be used to relay information to the operator. Remote controlling of machines has changed dramatically since the onset of the Internet, as operators can now control automated machines from locations hundreds of miles apart. This is particularly useful for controlling machines in environments not reachable by humans such as areas miles below the earth’s surface or deep in outer-space.

Vision-System-1

Operators responding to a visual display by manually controlling a machine is relatively straight forward compared to robots interpreting what is on a visual display and responding to this information. This is still deemed a daunting, if not impossible task by many engineers working in this field but biometrics has been used to resolve some of these shortcomings and vision systems are now widely used across many industries. Facial recognition technology is used in security systems as an alternative to electronic keys to provide a more secure access system. Facial structure, skin tone and eye colour can all be interpreted by these systems and access decisions can be made by cross checking this information with locally stored data. Although not perfect, vision systems are getting more competent at recognising human faces, tracking objects, deducing colour and interpreting three dimensional modelling.

Vision-System-2

There are still some deficiencies with these systems and we are a long way off relying on information outputted from these machines. In many applications the camera must be static to interpret accurately what is going on around it and this makes its use very impractical when attached to mobile systems.   Amongst other issues; they are unable to differentiate between sexes, objects in motion remain undetectable and the construct of objects is also beyond their functionality. The potential of this technology is great and at present we are only in the infancy of what we will one day be able to achieve with vision systems.

The Robotic Frame

23 Jul

When it comes to robotics, nothing causes more confusion than deciding on how to build the robot frame. The skeletal system that makes up a robot is a vital part of the build and designing it can prove difficult. Almost any material can be used to construct this artificial structure, except of course bone or any other biological material. Many materials are tested before the final material is chosen, as this will allow the fabricators to carry out certain tests on the machine. The application the robot is intended for is a major factor in making the final decision. It is important to use a strong robust alloy that can withstand various elements in a hazardous environment. A balance has to be struck between the strength of the material and the speed of application, as the two tend to be mutually exclusive in most applications.

Robotic machines tend to run on a local power source, such as an alkaline battery. This means that energy must be conserved wherever possible, as you do not want to be constantly charging your robot. The heavier the material used to build a robot and therefor the heavier the robot, the more energy the robot will consume when carrying out its job role. Lightweight materials are ideal for building these robots but these can be very expensive and difficult to work with. Below is a detailed overview of the most commonly used compound when building an automated machine.

Wood

It might seem surprising to you that I have listed wood on here but wood can be strong and lightweight at the same time. It is typical not what comes to mind when thinking about what to build a robot frame from but it should not be overlooked. Wood can be used to build anything from robot arms to disk-type machines but it is primarily used in prototypes only. The later application is a great way of saving money, as it will allow you to construct automated models for testing purposes before building the final product. Wood is not the most durable of material, as it has an inferior strength-weight ratio compared to other compounds in its class. It will also give your robot a dated somewhat comical look but as stated above for prototype purposes, it can be great.

Steel

Probably the most commonly used of them all, steel represents a material that has superior strength and robustness compare to other compounds. Unfortunately you pay for this extra durability with the added weight of the product, which will put a serious strain on your battery power. This can be overcome by fitting extra battery units but this can lead to a more cumbersome device. Budgeting for the use of steel, can pressurise other areas of the build and in some cases, using steel just isn’t a viable option.  If a significant degree of precision is required to construct the components of the robot, then stainless steel is often used for these applications. Again this adds further cost and weight overhead that need to be compensated for in other areas of the project.

Aluminium Alloy

When you are constructing a medium to large sized automated machine, Aluminium historically has been the material of choice. It’s lightweight, high strength and low-cost attribute make it an ideal compound to use when fabricating robotic parts. The shape of the aluminium structures used, can add extra strength to this already strong product, which can be easily worked on by standard workshop tools.  Aluminium is formed from a compound called Bauxite, which there is an abundance of all over the world. This means that this product is likely to remain low in cost for the foreseeable future.

Plastic

Plastic may not be the first element that comes to mind, when considering a frame structure for your automated machine but it is one that is actually used quite a bit. Acrylic resin is often used when building robotic frames, as it forms a very strong but light plexi-glass finish. This material can be moulded and shaped into any form, with relative ease and it is also an inexpensive material to work with. It bonds really well to itself, which will allow you to form strong unbreakable seems and joins. In many of the combat robots seen on TV, acrylic resin is often used for precisely the above reasons.

Titanium

When compared to other materials, Titanium provides more strength and is more lightweight. Given that these two attributes are highly sought after, Titanium is very expensive and quite are in terms of market exposure. Due to the high demand, more and more of this material is becoming available, so this has helped to drive the price down considerably. If this price continues to fall, the use of this material is conceivable regardless of the budgetary constraints. Titanium is fully expected to replace aluminium as the metal of choice for constructing metal frames.