Building a cobot cart: sturdy, smart and ready for the workplace | Cobots manual - part 1

Building a cobot cart: sturdy, smart and ready for the workplace

Why a cobot cart?

Would you like to deploy a cobot that is not fixed in one place, but moves flexibly with your production process? Then you need a stable and reliable cobot cart. But what points do you need to pay attention to during the design phase? This blog explains the main concerns as regards the frame, wheels, safety, couplings and positioning of the cobot. 

Frame: welded or modular?

The backbone of your cobot cart is the frame. There are two options: a welded steel frame or a profile construction in aluminium.
Welded steel frame:

• Very sturdy and stable thanks to heavier weight
• Ideal for fixed setups and harsh working environments
• Customisation requires welding expertise

Aluminium profile construction:

• Faster to build and easier to adapt afterwards
• Relatively cheap (around € 5,000 for our demonstration model)
• Lighter and therefore slightly less stable
   

Your choice depends on the way you want to use it and how much you want to be able to modify the design later. 

Important: there are electrical components built into the cart. These include both high- and low-voltage components. We chose to keep these separate to ensure safety when working on the low-voltage components (which is more frequent). The compartments in the cart where these components are located must also comply with the standards for building an electrical cabinet

Wheels: drive or non-drive?

The type of wheels determines how mobile your cobot cart is and the price:

• Non-drive wheels are the cheapest and suffice if the trolley does not need to be moved frequently
• Drive wheels are a good choice if the trolley needs to be moved frequently especially on sloping floors, they do however, require a battery
• Autonomous navigation based on AGV technology is technically feasible, but is currently too expensive for common SME applications
• The number of wheels is another factor to be considered. Tricycles are more stable when stationary, but slightly less so when moving, four-wheelers are easier, but can wobble on uneven floors

So make an informed choice. Depending on the alignment method chosen, stabilising feet or a docking mechanism are required to prevent the cart from moving while work is ongoing.
 

Worktop, grippers and couplings: think of the future

The worktop should be robust and suitable for clamping workpieces. Aluminium is often sufficient, but in heavy industrial environments it is worth opting for a harder material. Making space for a valve island is also important, even if your current applications do not require pneumatic components. Plan for the future and install it now. This way, your cart can be reconfigured when necessary.
Preferably use quick-disconnect connectors for power, safety and location coding. Avoid thick cables with multiple discrete I/Os. Instead, opt for fieldbus communication or wireless systems. They require a machine-side interface, but make disconnection so much easier and safer.

Cobot: positioning and range

The cobot itself is mounted on an intermediate plate on the worktop. (The demonstration cart is equipped with either a KUKA LBR iiwa or a Universal Robots UR10 but other cobots are, of course, also possible). This makes the system suitable for all types of cobots. The positioning of the cobot on the cart is crucial. A central position provides more stability, but sometimes limits the range of the cobot. Depending on the application, you need to find a compromise between range, stability and accessibility. In addition, be sure to note the difference between a cobot's maximum range and maximum payload: the two rarely coincide. The maximum advertised payload is rarely achievable when the cobot is at the extreme point of its range. If an application requires the cobot to operate at the limits of its range, keep in mind that the maximum payload will not be as large as the advertised payload.
 

Communication and safety: keep it clear

Cobot cart projects often come up against limitations in the cobot's standard I/Os. An extension with a gateway module (e.g. a RevPi) helps to convert protocols and reduce physical connections. This keeps the cabling clear and the connectors small. For safety reasons, the use of a safety PLC and scanner (e.g. from Sick) is highly recommended, ensuring that the cobot stops as soon as an operator enters the safety zone.
 

Modular base, thoughtful design

So a good cobot cart is stable, reconfigurable and safe.
It combines:

• A rigid or flexible frame
• The right type of wheels for your application
• A well-chosen worktop with forward-looking features
• Strategic positioning of the cobot
• And secure, modular communication components