Compensating Thermal Effects in Mechatronic Systems
Mechanical automation has infiltrated all aspects of modern life and is here to stay. Anyone that has played with their home thermostat is already familiar with the nature of control systems: you adjust the thermostat in order to control when your HVAC unit switches on and off with the goal of maintaining a stable temperature throughout your home.
Control systems are becoming more sophisticated in order to provide faster response time, eliminate transient effects in control loops, and generally broaden their applications into new areas. Autonomous automobiles, industrial systems, and even smart home systems will all benefit from novel control systems.
Mechatronic Control Systems: A High-level View
Any mechatronic system requires a sophisticated active control system to maintain the motion or other activities in the system. In the event of some unanticipated disturbance, such as a mechanical shock or power surge, the control system will need to quickly compensate for the disturbance and try to keep the mechanical portion of the system working as smoothly as possible. The objective is to electronically automate a certain process while maintaining important parameters within the system at stable values.
In general, there are two types of control systems that are used in mechatronics: sequential control and continuous control. In sequential control, all operations in the system are carried out in a specific sequence with a specific order. The most commonly cited example of a sequential control system is an automated assembly machine on a production line. Sequential control systems use a programmable logic controller (PLC) to execute a specific sequence of operations.
In a continuous control system, a proportional-integral-derivative (PID) controller is used to continuously measure a signal in the system and make adjustments to the inputs of the system. In essence, this is a system that requires continuously monitoring either a digital or analog signal that is output from the system. The goal in these systems is to maintain a specific output or set of outputs from the system at stable values.
Finally, each type of system operates with feedback (closed-loop system) or without feedback (open-loop system). In a closed-loop system, the output is routed back into the input of the system. The output could be conditioned in some way before entering the input of the control system. A great example of an electronic device that is a continuous closed-loop control system is a phase-locked loop. In contrast, an open loop system does not route the output back into the input of the system. In effect, the output has no influence over the system.
This manufacturing system will inevitably require a thermal control system
Addressing Thermal Effects in Mechatronic Control Systems
The level of control required in a given system and its implementation on a PCB really depends on the relevant application. The required precision on automated manufacturing equipment can range from millimeters to nanometers. Mechatronic welding robots do not require the same level of positional precision compared to semiconductor lithography equipment for integrated circuits. In extremely high magnification imaging systems and applications, heat generated in electronic and optical components can lead to thermal drift in an image, which decreases the resolution in captured images.
In any mechatronic system, increasing the temperature increases the errors in the system due to increased Johnson noise and thermal expansion of mechanical components. In systems that reach higher temperature, active, closed-loop control should be used to compensate temperature rise in the system. Offset errors and the required compensation will generally increase with temperature, thus stable active cooling of the mechatronic system itself may be desirable.
Whether your PCB will operate as a purely digital, purely analog, or mixed-signal device will depend on the type of sensors involved in the control loop, the output from the control loop, and signal used to drive mechanical elements in a mechatronic system. Many mechatronic systems are driven with high-precision servo stepper motors that are controlled with pulse width modulation, so the board for controlling these systems will likely operate as a mixed signal device.
Testing temperature sensors is invaluable to ensure accurate measurements
Sensors that are very sensitive to temperature changes require precise calibration and processing temperature measurement during operation in order to convert their electrical output to an accurate temperature measurement. The required compensation determined during calibration at different temperatures will then need to be implemented in the control system. This method, as well as the overall operation of the control system itself, can be easily implemented with an MCU, ASIC, FPGA, or another controller.
Aside from controlling or compensating thermal effects in mechatronic systems, thermal management should be considered on the PCB housing the control system itself. Active control systems require active components that can generate their own heat, thus thermal management in these systems becomes very important. This is especially the case when working with sensor arrays, as heat generated in sensor arrays will influence their signal-to-noise ratio, sensitivity, and even their dynamic range.
When you need to design a board for a high power PCB with high thermal conductivity, you need the right PCB layout and design software with a full suite of design tools. Allegro PCB Designer and Cadence’s analysis tools can help you design the right stackup for your system and simulate thermal demands in your device.
If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.