3D Tool Strengthens Marriage of PCB Design with Mechanical Design

Cadence Design Systems has announced its Cadence Sigrity 2018 release, which includes new 3D capabilities that enable PCB design teams to accelerate design cycles while optimizing cost and performance. According to the company, a 3D design and 3D analysis environment integrating Sigrity tools with Cadence Allegro technology provides a more efficient and less error-prone solution than current alternatives using third-party modeling tools, saving days of design cycle time and reducing risk.

In addition, a new 3D Workbench methodology bridges the gap between the mechanical and electrical domains, allowing product development teams to analyze signals that cross multiple boards quickly and accurately.

Since many high-speed signals cross PCB boundaries, effective signal integrity analysis must encompass the signal source and destination die, as well as the intervening interconnect and return path including connectors, cables, sockets and other mechanical structures.

Traditional analysis techniques utilize a separate model for each piece of interconnect and cascade these models together in a circuit simulation tool, which can be an error-prone process due to the 3D nature of the transition from the PCB to the connector. In addition, since the 3D transition can make or break signal integrity, at very high speeds designers also want to optimize the transition from the connector to the PCB or the socket to the PCB.

According to the company, the Sigrity 2018 release enables designers to take a holistic view of their system, extending design and analysis beyond the package and board to also include connectors and cables. An integrated 3D design and 3D analysis environment lets PCB design teams optimize the high-speed interconnect of PCBs and IC packages in the Sigrity tool and automatically implement the optimized PCB and IC package interconnect in Allegro PCB, Allegro Package Designer or Allegro SiP Layout without the need to redraw.
Until now, this has been an error-prone, manual effort requiring careful validation. By automating this process, the Sigrity 2018 release reduces risk, saves designers hours of re-drawing and re-editing and can save days of design cycle time by eliminating editing errors not found until the prototype reaches the lab. This reduces prototype iterations and potentially saves hundreds of thousands of dollars by avoiding re-spins and schedule delays.

A new 3D Workbench utility available with the Sigrity 2018 release bridges the mechanical components and the electronic design of PCB and IC packages, allowing connectors, cables, sockets and the PCB breakout to be modeled as one with no double counting of any of the routing on the board. Interconnect models are divided at a point where the signals are more 2D in nature and predictable. By allowing 3D extraction to be performed only when needed and fast, accurate 2D hybrid-solver extraction to be performed on the remaining structures before all the interconnect models are stitched back together, full end-to-end channel analysis can be performed efficiently and accurately of signals crossing multiple boards.

In addition, the Sigrity 2018 release offers Rigid-Flex support for field solvers such as the Sigrity PowerSI technology, enabling robust analysis of high-speed signals that pass from rigid PCB materials to flexible materials. Design teams developing Rigid-Flex designs can now use the same techniques previously used only on rigid PCB designs, creating continuity in analysis practices while PCB manufacturing and material processes continue to evolve.

Cadence | www.cadence.com

Designing a Home Cleaning Robot (Part 2)

Part 2: Mechanical Design

Continuing with this four-part article series about building a home cleaning robot, Nishant and Jesudasan discuss the mechanical aspects of the design.

By Nishant Mittal and Jesudasan Moses
Cypress Semiconductor

In part one (Circuit Cellar 329, December 2017) of this home cleaning robot article series, I discussed the introduction to the concepts of cleaning robots and the crucial design elements that are part of a skeleton design. Apart from that I discussed various selection criteria of the components. In this part, with the help of my colleague Jesudasan Moses, I’ll explore the mechanical aspects of the design. This includes selecting materials, aligning all the components on base, designing the pulleys for optimal performance, selecting motors and so on. The mechanical design for such a system can be very challenging because it’s a moving system and that adds complexity to the process. While this part is focused on mechanical issues and making the base ready, all this paves the way for when we add the “brains” into the system in part three.

DESIGN ELEMENTS

Figure 1 shows the block diagram of the mechanical design for this project. The overall structure of this design requires a base that is strong, but not too heavy. Using a metal base isn’t a good option for this type of system because it would increase the overall weight. Such an increase might mean that a higher torque motor would be required. The next elements are the motors and wheels. We chose to include motors only in the back. Using a front motor would probably be an overdesign for such a system. If you examine professionally designed home cleaning robots—like those I covered in part one—all of them had only the back motors for movement.

Figure 1
Mechanical arrangement of the home cleaning robot

On the front side of the unit, only rollers are added. This gives the system a complete 360-degree freedom of movement. The most important parts of the system are the cleaner and the roller. These are placed toward the center of the system and are controlled using an arrangement of motors and pulleys. In the front of the system, side brushes are added that again are controlled using motors. Now let’s look at the selection of each of the design elements.

Selection of the base shape: The base shape selection is very important because it defines how efficiently your home cleaning robot can clean at corners. A circular base shape is the most recommended option. A circular base enables the robot to move around corners and thereby cover each and every part of the house. That said, for a hobby project like this one, a rectangular base means no advanced tools are needed to cut and shape the base. With that in mind, we chose to use an acrylic material in a square shape for the base.

Motor selection: For our design, we opted for two movement motors on the back of the unit and another motor at the back for the roller pulley. On the front, there are two more motors to move the side brushes. We’ll save the more technical discussion about motor selection in part three. Choice of motor size depends upon the total weight that the front and back need to handle. The total weight should be equalized, otherwise the system won’t remain stable when the robot is moving fast. The placement of the two movement motors should be aligned to their center of axis. That ensures that when the robot is moving straight, it won’t divert its direction. It’s also important to buy those two motors from the same vendor to make sure they share the same mechanical properties.

Wheel Selection: It’s very important to decide on the net height of the system early on. Wheel selection is the deciding factor for the net height. .

Read the full article in the January 330 issue of Circuit Cellar

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