FEATURE Sensors
Application-specifi c position sensors for robots
Dr Mike Coulson, Analogue Design Manager at Swindon Silicon Systems, explains the importance of having application-specific devices for the new generation robots
T
here were some three million industrial robots operating in factories around the world in 2020. Each of them relies on
numerous sensors, some of which position sensors that measure rotation and linear displacement, among their other tasks. A rotary encoder measures the angle of a robotic arm joint, whereas a linear encoder will report the position of a cartesian robot along a particular axis.
The encoder includes a sensing element that converts a physical stimulus into an electric signal. In an inductive encoder, this is a coil detecting a changing magnetic environment – say a slotted ferrous metal scale. In an optical encoder, the sensing element may be a phototransistor. Each type features excitation circuitry to create the stimulus and a signal-conditioning circuit to amplify the weak electrical response.
Increased integration When prototyping encoders, normally its components are off -the-shelf ICs, such as discrete capacitors and resistors. However, to reach a class-leading performance, developing an ASIC is justifi ed since developers can integrate as many functionalities as possible into a single package.
Industrial robots serve as an example of an application where position sensors are expected to operate continuously; any maintenance downtime incurs cost and inconvenience. The solder joints of a circuit board are a common failure location, so it makes sense to reduce component count by replacing various discrete components and standard ICs with a single, highly- rugged package. In this way the electronics are aff orded greater protection from environmental factors such as chemical attack and vibration, and assembly of the PCB becomes simpler. In addition, the size of the PCB is reduced, leading to a smaller and lighter encoder that off ers improved dynamics, and is able to serve new applications. Some customers also value the protection an ASIC aff ords for their circuit IP, as monolithically-integrated circuits are
36 April 2022 | Automation
[Image: Simon Kadula for Unsplash]
far more diffi cult to reverse engineer than a collection of standard parts wired together in plain sight. What’s more, an ASIC brings opportunity
to reduce part cost. Systems built from off - the-shelf components are frequently over- engineered, as standard parts are designed and sold with maximum versatility in mind. Swindon will assess its customers’ systems and hunt out every opportunity to squeeze cost from the design: is that CPU really necessary, if we could synthesise hard-coded logic for a fraction of the price? Is that dual-channel ADC used to capacity? Through ASIC design, customers can invest in performance where it matters.
The process of ASIC development A company should consider whether a project is ready to benefi t from a custom ASIC as soon as a prototype exists. At this point, a supplier like Swindon Silicon Systems will assess whether a custom solution is for them, and identify the best possible system partitioning. It is common, but not always necessary, for a supplier to undertake a four- to eight-week feasibility study to inform these conclusions and arrive at a detailed proposition and costing. The supplier will then develop the chip, breaking the design down into analogue and digital blocks. At this stage, many
customers benefi t from receiving a detailed behavioural model, in VHDL for example, to allow co-simulation with the rest of their system.
Beyond this, the work is fi rmly in the supplier’s hands, and no more resource is required from the customer, apart from periodic reviews to demonstrate the growing maturity of the design and its verifi cation. The timescale of the entire process from specifi cation to silicon will depend on the complexity. But in every case, it is essential to work with an ASIC supplier who can own all aspects of the project, from the initial consultancy to the ongoing supply of qualifi ed production parts.
Position sensors underpin modern industry and continue to evolve in their performance and technology. The sensor electronics are a key part of this evolution, having direct infl uence on speed, accuracy and overall form factor. Whilst off -the- shelf components suit some applications, manufacturers looking to truly diff erentiate their products must take the next step and explore the benefi ts off ered by a custom IC.
CONTACT:
Swindon Silicon Systems
www.swindonsilicon.com
automationmagazine.co.uk
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