Decline Accumulation Conveyor: The Holy Grail of Material Handling

Wednesday, August 31st, 2011

Obtaining cost effective, belted accumulation on a decline is one of the holy grails of material handling systems. In systems that have a sorter before shipping lanes, accumulation provides buffer to the shipping lane, and the decline allows for a smaller accumulation footprint.

This is also true for declines that feed box toppers, shipping labels, or some other important process that requires singulation and product buffer. Once the decline angle and product weight require belted accumulation, the options to the system integration engineer narrow and become expensive.

With this in mind, Blue Arc Engineering introduced a belted, decline accumulation conveyor to the ZiPline product line that provides unique features unparalleled by other belted accumulation conveyors in the marketplace.

While developing ZiPline, a 24 Volt accumulating conveyor, we assumed that decline accumulation would be an easy design carryover from the horizontal and incline accumulation designs. What we found was a problem that many 24V conveyor manufacturers run into; it is difficult to control the speed on a decline once the product weight and decline angle cross a threshold.

The analogy to this is cruise control in your vehicle: as you descend a hill, the cruise control does not slow the car down. In a nutshell, it is much easier to add energy to a system to obtain a desired output than it is to take energy out to reach a desired output.

When you take energy out, it requires monitoring of the output as well as ensuring that you take energy out at a reasonable rate to not cause a violent shock to the system. This is a limitation of using a mechanical brake inside of motorized drive roller (MDR); the brake is either all the way on, or all the way off.

We evaluated several options to remove this energy in a controlled way, as shown in the table below.

Click to View a Larger Version of this Chart

Method 4 was chosen after some development and testing of different components to find the right setup that worked reliably.

When the electromechanical (EM) brake turns on, the resulting regenerated energy turns into an increase in voltage. This voltage increase is what needs to be monitored to ensure that the peak value does not cause any problems with the MDR control card, the field wiring, or the power supply.

The two scenarios covered in the graphs below show the increase in voltage for different weights at 140 feet per minute.

Click to View a Larger Version of this Chart

In conclusion, using an EM method to reliably introduce cruise control for belted accumulation is cost effective and reliable. Solving this problem with software causes no change to mechanical elements that make up the standard ZiPline conveyor, making it an easy option to decrease overall footprint of a system while increasing the flexibility and throughput with accumulation.

For more information, visit the ZiPline Decline Accumulation Conveyor Webpage.

The Power of Cubic Functions for Engineers

Friday, August 5th, 2011

In the master’s classes in which I am currently enrolled, cubic polynomials continue to re-emerge as a useful tool. In robotics systems, the cubic polynomial is a useful function for calculating trajectories for robotic manipulators.

In design optimization methods, it is used to find the minimum or maximum of an unknown two-dimensional analytical function while only knowing the function evaluation to four dispersed points. However, for the purpose of this article, I would like to discuss the benefits of using cubic polynomials in trajectory calculations.

Validating a design concept in a material handling system typically involves calculating throughput. Before I was more familiar with cubic polynomials, I would use constant acceleration equations with many piecewise functions to determine the total throughput for a system. This is sometimes called Linear Segment with Parabolic Blends (LSPB) or Trapezoidal Velocity Profile, and the trajectory charts would typically look like this (click on charts to enlarge):

This motion profile is the most accurate, but it requires the engineer to make some guesses about the time to start constant velocity and the time to end it. This is not difficult from spreadsheet to template, but what if you wanted to move from the trapezoidal-shaped velocity curve to a triangular shape? The builder of the spreadsheet then has to fill in if statements or create an entirely new spreadsheet. If you use a cubic polynomial, the trajectory charts look a little less familiar:

When compared to the constant acceleration or trapezoidal velocity profile the differences become more obvious:

Immediately apparent is the velocity and distance trajectories look close, while the acceleration plot is vastly different. The acceleration will always be higher on the cubic representation of the trajectory, but this will aid in a conservative estimate while doing initial throughput calculations.

In this example, the difference between actual acceleration and the cubic representation of acceleration is around 33%. Another caveat to this approach is that acceleration is changing linearly with time, producing jerk.

The adage “every model of physical reality is wrong, but some models are useful” comes into play here. This approach could be particularly useful as a bridge between the arbitrary values entered into a spreadsheet and a detailed analysis that allows the user to order motors for a particular machine or material handling system.

A cubic polynomial approach would give you a “one-hour answer” very quickly because for each actuation you only need to know two things, distance traveled and final time. After those two values are decided, you can calculate horsepower and other important characteristics in your motion profiles with order-of-magnitude accuracy.

In conclusion, understanding the sensitivities of your system design is an important litmus test on the feasibility of your approach. Using a cubic polynomial representation allows the engineer to build a spreadsheet to evaluate the design and understand and quantify the cost of each actuation to overall cycle time.

Reference:
Mark W. Spong, Robot Modeling and Control 2006

It’s hot in here! Developing Automation for Extreme Environments

Wednesday, June 29th, 2011

With the right talent, experience, and tools, the sky is the limit when it comes to solving new engineering problems. Lately much of our research and development has been related to developing custom solutions for very specialized extreme environments.

In the past, our equipment has been able to withstand heavy loads, abrasive materials, explosion prone areas, and wash down.  However, today, the equipment we design is being tasked to not only survive, but thrive in extreme heats in excess of 2,000 degrees F, as well as high level vacuum.

In a vacuum where there is no atmosphere present, two unique problems make it difficult to reach ultimate vacuum:

1. Motors can’t cool themselves
2. Components can outgas

To combat these problems, my research teams have partnered with advanced component suppliers to provide parts and materials that meet these extreme heat and vacuum standards.

The first step was to use rated motors originally designed for space programs, meaning they didn’t outgas.  We also used state-of-the-art alloys and materials that can insulate under extreme heat or absorb and withstand it.

These extreme conditions also provide unique engineering parameters, making predictive tools a necessary part of our design equation. By utilizing the latest finite element analysis tools to accurately predict loading and heat transfer, the upfront risk is minimized and confidence can be gained early in the design cycle.

Vacuum can be a tricky art, and sealing a chamber with moving components and electronics is a true feat.  To combat this, our design team fabricated some unique solutions for passing power and control through a vacuum chamber.  They also created a solution that allowed remote mounting actuators, motors, and moving shafts to pass through a sealed vacuum chamber.

For extreme loads in excess of tens of thousands of pounds, we have developed ways to accurately and quickly control our motion in any environment. Our past projects have included accuracy and repeatability of .003″ for massive loads over distances as long as 40 feet.

During these research and development projects, we have utilized a combination of fiber optic sensors, Temposonics, absolute encoders, steppers, and AC motors to effectively match any speed or accuracy available at atmosphere.

As we look to the future, our R&D team is continually staying on the cutting edge of new technologies. We will be looking at further improving our designs as well as finding environments where automation was previously thought impossible or not cost effective.

Our engineering process also lends itself well to partnered engineering studies in which we keep the customer involved in every step to insure our designs are meeting every need. This can be a valuable tool that minimizes risk for both parties when undertaking ground up design.

Automation for these types of extreme environments is the next essential step in safety, cost control, and efficiency.