How has the approach to complexity in mechanical systems changed over time?

Historically, the challenge was building complexity into mechanical systems, often through intricate mechanical linkages. Now, with compact and affordable computation, the challenge has shifted to managing the complexity we can create, with software complexity being the main limit.

What are some historical examples of mechanical control and computation?

Early examples include the steam engine's mechanical controls for valves, James Watt's flyball governor for speed regulation, and the Jacquard loom's use of punch cards for intricate pattern weaving, demonstrating early forms of mechanical computation and control.

Why was the invention of the brushless motor a significant step in mechatronics?

The brushless motor separated sensing, computation, and amplification functions from the direct power path, unlike brushed motors where these were integrated. This separation allowed for optimization of each component using available technologies, leading to higher performance and reduced maintenance.

What is the significance of reusable and reproducible software in mechanical control?

Software's data reproducibility means running a program yields the same result consistently, unlike analog systems where noise can propagate and limit complexity. This magic of digital systems allows for error-free propagation and virtually no complexity limits.

What are the challenges of real-time software in mechatronics?

Real-time software needs predictable timing. While digital systems offer reproducibility, they aren't always time-predictable due to operating system environments. For mechatronics, statistical timing is often sufficient, and the asynchronous nature of mechanical systems adds further challenges.

What is the 'unit machine' concept in mechatronics design?

The unit machine defines the fundamental elements of a system that directly exchange power or material with minimal buffering. The key design decision is selecting a unit machine size that balances manageability of complexity with the ability to optimize the system.

How does the concept of a 'unit machine' apply to real-world design failures?

Defining the unit machine too small can lead to systems like the semiconductor wafer handling example, where optimization is hindered. Conversely, defining it too large, as with the Denver Airport's baggage system, can result in catastrophic failure.

What design language and methodology does Berkeley Process Control use?

They use a model based on tasks and finite state machines, with tasks mapping to hardware and higher levels being goal-oriented. State machines provide a clear, visual way to describe task logic, facilitating communication and design.

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Mechatronics Mechanical System Control - It's the Software!

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Education6 min read54 min video

Aug 22, 2012|6,803 views|31|1

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TL;DR

Software has completely revolutionized mechanical control, making it the primary driver of complexity and performance, rather than hardware. Ignoring software costs in BOM accounting leads to unreliable, slower-to-market products.

Key Insights

The value added in mechatronics has shifted from electronics to software, with software now being the real driver of mechanical system complexity and capability.

Historically, mechanical systems integrated sensing, computation, and power transmission (e.g., Watt Governor, brushed DC motor); modern mechatronics separates these functions using electronics and software.

Compact and affordable computation, particularly microprocessors, has made software the cheapest way to control power modulation in mechanical systems.

While digital software offers error-free information processing, real-time software faces challenges with timing reproducibility due to operating systems and asynchronous events.

A fundamental design principle is to replace mechanical components primarily used for information transmission or computation with software or electronics.

The cost of software is often unaccounted for in traditional Bill of Materials (BOM) accounting, leading to the selection of cheaper but less capable hardware and increased development costs.

The shift from mechanical complexity to software-driven control

The field of mechanical system control has undergone a dramatic transformation. Historically, the challenge was to build complexity into mechanical systems. However, with the advent of mechatronics – the integration of mechanics and electronics – this paradigm has inverted. Today, the primary driver of complexity and innovation in mechanical systems is software. The term 'mechatronics' itself, coined in the early 1970s by Yaskawa Electric to describe brushless motors, initially represented the synergy of mechanics and electronics. However, the subsequent integration of software has proven to be an even more significant disruptive force, fundamentally changing the rules, capabilities, and design considerations in mechanical system control.

Historical roots: Mechanical computation and control

To understand the current landscape, it's crucial to look at historical precedents where complexity was managed through mechanical means. Early steam engines, like the Newcomen engine (circa 1760), used intricate mechanical gadgetry to operate valves at precise times, essentially implementing control logic mechanically. Later, the Watt Governor (19th century) integrated sensing (flyball speed), computation (centrifugal force), and actuation (steam valve control) into a single mechanical assembly to maintain constant engine speed. The Jacquard loom, also from the 19th century, used punch cards to control complex weaving patterns, demonstrating a form of programmable control. These examples highlight a key characteristic of older systems: a lack of separation between sensing, computation, and power transmission, often with a direct power path from sensing to actuation.

The impact of electronics: Separating functions

The introduction of electronics, particularly with technologies like the vacuum tube (leading to solid-state amplification), began to enable the separation of sensing, computation, and actuation. A prime example is the transition from brushed DC motors to brushless motors. In a brushed motor, the commutator performs the crucial task of reversing current direction based on rotor position, integrating computation directly into the power path. Brushless motors, however, eliminate the brushes and replace this function with electronic sensing, computation, and amplification. This separation allows for independent optimization of each component, leading to higher power density, improved reliability, and reduced maintenance compared to brushed motors where voltage is limited by brush sparking. This separation of concerns was a critical step towards modern mechatronics.

The software revolution: Complexity and cost-effectiveness

The advent of compact and affordable computation, catalyzed by microprocessors, has cemented software's role as the core of mechanical system control. Today, for most applications involving the modulation of power, controlling the system with a computer is the cheapest and most flexible approach. This shift means that control complexity is now largely limited only by software complexity, rather than hardware constraints. The inherent advantage of digital software lies in its data reproducibility – running a program yields the same results consistently. This contrasts sharply with analog systems, where complexity is ultimately limited by signal-to-noise ratios and error propagation. While digital systems offer this remarkable error-free domain, it's built upon the foundational concept of binary representation, which, though seemingly inefficient (one bit per wire), is key to preventing error propagation.

Real-time challenges: The timing problem

Despite the advantages of digital computation, real-time software introduces unique challenges. While software is data reproducible, it is not always time reproducible. Variations in operating system scheduling, background processes, and hardware interrupts can lead to unpredictable execution times for tasks, even simple loops. For mechatronics, where precise timing is often critical, this unpredictability can be a significant issue. The concept of 'hard real-time' systems, which demand absolute deadlines, is less common in mechatronics than 'statistically reproducible timing.' Furthermore, the asynchronous nature of many mechanical events means that deterministic scheduling is often impossible, turning processor activity into a statistical rather than a guaranteed outcome.

Design principle: Replace mechanical information transmission with software

A core design principle emerging from this shift is to identify and replace mechanical components that primarily serve to transmit or compute information with software or electronic equivalents. Examples abound: replacing carburetors with electronic fuel injection, eliminating mechanical linkages and cams in favor of motor control profiles, and using variable speed motors instead of air dampers for airflow control. By unbundling these functions, designers can achieve greater precision, flexibility, and performance. This approach prioritizes modularity and the use of software to manage the inherent complexities that were once managed, often arduously, by mechanical means.

The 'Unit Machine': Defining the scope of control

A critical design consideration in mechatronics is the definition of the 'unit machine' – the scope of elements that directly exchange power or material with minimal buffering. Selecting the appropriate unit machine is crucial: too large, and managing complexity becomes difficult; too small, and optimization opportunities are lost due to excessive modularization. Poor definition of the unit machine can lead to underperformance or unreliability. For instance, in semiconductor manufacturing, defining individual robots as separate unit machines led to a 3.5x performance improvement when a single controller managed multiple robots, allowing for more efficient handoffs and reduced exclusion zones. Conversely, the Denver International Airport baggage handling system is cited as an example of defining the unit machine too broadly, integrating too many disparate functions into a single, unmanageable entity that ultimately failed.

The overlooked cost of software and accounting discrepancies

A significant practical challenge is the traditional accounting practice that often excludes software costs from the Bill of Materials (BOM). While hardware components like ROM chips might be listed, the development time, testing, and ongoing maintenance of sophisticated control software are frequently omitted. This 'phony accounting' leads to decision-making based on incomplete cost information, such as opting for cheaper processors that strain software development efforts. The result can be unreliable systems, missed deadlines, and increased overall project costs, as control engineers must resort to 'heroics' to make less capable hardware meet performance specifications. Recognizing software as a critical, and often expensive, component is essential for successful system design and cost management.

Mentioned in This Episode

●Companies

●People Referenced

Mechatronics Design Principles

Practical takeaways from this episode

Do This

If a mechanical component transmits information, consider replacing it with software or electronics.

Design the 'unit machine' appropriately: not too big to manage complexity, not too small to optimize.

Focus on mapping design to software for portability and maintainability.

Use cooperative multitasking and write non-blocking code for real-time systems.

Break long computations into smaller, manageable pieces within a state machine framework.

Treat software development as a critical component of the overall machine cost, not an afterthought.

Avoid This

Do not allow mechanical components to perform both sensing and power transmission if avoidable.

Do not define unit machines too small, as it can hinder overall system optimization.

Do not define unit machines too large, as it can lead to unmanageable complexity and system failure.

Avoid relying solely on interrupts for real-time mechanical system control; prefer cooperative multitasking.

Do not ignore the cost and impact of software on the bill of materials and time-to-market.

Common Questions

Mechatronics is the synergy of mechanics and electronics, a term coined in the early 1970s. Today, software has become the primary driver of value in mechatronics, dramatically changing the field by enabling complex decision-making and control in physical systems.

Topics

Technology & Innovation Science & Mathematics Software Engineering State Machines Real-time Systems Embedded Systems Mechanical System Control Design Methodology Feedback Control

Mentioned in this video

Companies

Google

The host company, where many employees work in programming, a field that intersects with mechatronics.

Yaskawa Electric

Company that coined the term 'mechatronics' in the early 1970s to describe brushless motors.

Berkeley Process Control

A company co-founded by the speaker, which applies specific design methodologies for semiconductor machines and controllers.

People

James Watt

Steam engine manufacturer who invented the Watt Governor, a device for regulating steam engine speed.

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