Robotic total station

This article was written by Chris Slinn, MEP Business Development at Amtech, a Trimble company, a manufacturer of specialist software for the building services industry. It originally appeared as a BSRIA blog post in March 2015. The original post can be seen here.

[edit] Introduction

Since the days of the Latham report in 1994 there has been a desire to cut the cost of construction, mainly by finding more efficient ways of doing things. Of course, there will always be people who stick rigidly to the principle that ‘the old ways are the best’, but there are many more who are more open-minded – not least in terms of making use of new technologies.

Having said that, there is one particular technology that has not yet been embraced in the UK, despite the significant financial and time benefits that have been shown time and again in the USA and other countries - the use of Robotic Total Stations (RTSs) for laying out building services – as an alternative to the traditional ‘tape measure, spirit level and theodolite’ approach.

This article considers the limitations of traditional methods and explains how RTS technology can help to overcome them. It also explores some of the reasons that this technology has not yet been widely adopted in the UK.

[edit] Are the old ways the best?

Traditionally, the layout of building services on site has involved a team working from the building drawings, using a tape measure, spirit level and theodolite to identify attachment points for pipework, cable trays etc. Unfortunately, this system doesn’t work particularly well with complex buildings, buildings with curved walls, buildings with prefabricated materials, BIM or non-orthogonal spaces. In fact there is a huge margin for error, resulting from the following challenges:

• Ensuring the reference point is right.
• Making sure the tape measure doesn’t move.
• Making sure the string doesn’t move on arcs.
• Ensuring the theodolite is level.
• Making sure the degree in which you are measuring is exact.

Every small mistake can lead to potentially serious consequences. For example, being a few degrees out on an angle can mean that pre-fabricated systems don’t fit when the time comes to install them. Similarly, incorrect layout can result in clashes with other building elements or services, thereby disrupting the construction schedule, generating remedial works and wasting materials, time and money.

Even when everything goes smoothly, the traditional approach is laborious and time-consuming and any delays can affect the work of other teams.

When changes need to be made, methods of recording reasons (obstruction etc.) and evidence (photographs etc.) are recorded additionally to any drawings they are working from. These reasons are sometimes reported to the design team (if there is one) to amend the drawings or model; at other times, these records are filed separately for the purposes of finger-pointing at a later date. Either way, it takes a long time for this information to be reflected in the designs, if at all, which means other contractors or labour forces won’t see the changes until they’re updated. Working from paper also has the potential for loss or damage.

These issues are going to become more serious with the wider use of Building Information Modelling.

[edit] An alternative approach

Robotic Total Stations (RTS) allow layout to be completed by just one person, rather than the classic layout team.

To begin construction layout, a tablet with software controls the RTS and is loaded with a 2D drawing or 3D building model. Site survey points from the job site are identified in the model and are used to locate the RTS on the project site and in the model. Once the RTS is located, the person operating the RTS can view the model on the tablet computer and select the points to be marked. Once selected, the RTS will tell the operator their precise distance from the point (if using a stake) and then guide the user to the point with directions indicating forward/backward or left/right movement. The operator then stakes the mark and moves to the next one.

A more advanced RTS feature is Visual Layout which marks the layout point with a laser (removing the need for the stake); the operator then only has to follow the laser to each point and mark the location. Basically, the RTS does all the work while the operator follows its laser, marking each point to within a distance of millimetres from the 2D/3D model point. This can be used for the accurate positioning of multiple trades at the same time, ensuring no delays on site.

So what are the benefits?

• Improved efficiency: RTSs use the same 2D drawings or 3D building models as other trades involved in the project, so collaboration is simpler and quicker.
• Enhanced accuracy: Layout coordinates can be accessed directly from the building model and changes to layout positions can be recorded at the time of layout and documented with reasons and photographs.
• Fewer mistakes: The RTS works directly from the building model. There are no manual measuring processes involved. Points to be marked are extremely accurate and their purpose is referenced to the operator via their tablet device.
• Reduced paperwork: Using the RTS on a job is a paperless process, meaning there is no risk of losing documents or spilling coffee on them.
• Reduced labour costs: The RTS only needs one person to operate it and that one person is also capable of increasing layout productivity by up to five times.
• Improved quality control: RTSs can be used as a sophisticated tool in a QA/QC process, both pre- and post-installation.

[edit] BIM-to-Field

As we move to more sophisticated BIM processes – such as 4D & 5D BIM that includes building production models and which consider the constraints of a construction site (equipment capacity, working methods etc.), model based estimating and more – a live link to the field is needed. This link, in part, can be provided with the use of an RTS, allowing responsible parties to track works as they are completed and referenced against the original model, applying changes where necessary and allowing the tracking of works ready for access by the next stage in the construction process.

[edit] So why aren’t we using them?

Companies across the US have used RTSs on construction sites for many years now. They’ve been highly popular with MEP contractors and revolutionised layout processes and BIM progression; so why don’t we use them? A lot of it simply comes down to misconceptions about the technology and its uses.

[edit] Return on investment.

Implementing RTS technology requires capital investment and many companies feel that because they don’t have dedicated layout teams they won’t see a good return on their investment. However, the relative simplicity of RTS technology means that any member of the MEP team can carry out accurate layouts, so the contractor can make better use of the workforce.

Also, RTS eliminates manual errors so that the most highly skilled and best trained individuals can be allocated to the more complex tasks, while lower skilled operatives do the laying out.

In addition there are considerable time savings that could ultimately reduce the number of operatives required on the project, thus reducing labour costs.

You can calculate your own ROI here

[edit] The savings cited for RTS do not have any real impact on the bottom line.

This is simply not true. Savings from the use of an RTS can be seen in:

• Reduced remedial works due to increase in QC/QA documentation and recording – an immediate reduction in cost.
• Improved efficiency whilst on site – reduction in labour cost.
• Fewer errors in MEP element locations (another remedial work saving) – an immediate reduction in cost.
• Reduced resource required to complete works – an immediate reduction in cost.

[edit] MEP designs evolve during installation so that the drawings do not represent the actual situation.

Perhaps this is true today, but if you are working this way now, you won’t be for long. For medium and large projects MEP data and detailed design will be as essential as structural design as the industry assimilates the BIM process. Businesses looking to grow, or large businesses looking to remain profitable, will need to ensure they can work in these parameters – and soon.

[edit] Clashes between services do not occur when the same contractor is doing all of the MEP work.

On small projects it is often possible to ‘work around’ any clashes between services. However, on larger projects it is not enough to ask for one element to be placed over/below/around another, as this may then run into a second clash with a third element. This second work around would involve a wider rectification, which may infringe on another element, and so on until a solution cannot be made. Eventually, it may occur that an MEP element then interferes with the installation of another contractor’s or team’s work.

Also, when ‘working around’ an issue, we create problems when considering building maintenance post-construction, as MEP elements will deviate from their logical course.

[edit] UK construction techniques do not lend themselves to using an RTS.

While it’s true there are some differences between UK and US construction methods, there are many more areas where RTS can deliver the same benefits to UK contractors as it is already doing for US contractors.

[edit] Conclusion

While any investment in new technology clearly requires careful consideration, RTS is certainly worthy of that consideration. The potential benefits to MEP contractors are enormous, so it’s worth taking the time to keep an open mind and take a closer look.

--BSRIA