Case Study: RealTime Shredding

March 17, 2008

Impulse Engineering

Bruce W. Pearman, MSEE

Early in 2005 I met with the owner of JRP Enterprises, a company with an idea for a new public access vending kiosk. It was initially envisioned as an industrial strength, self-contained, high-quality shredder sophisticated enough to be operated with minimal intervention and service and safe enough to be left unattended. After most of the R&D was completed a new company was formed called RealTime Shredding, Inc. ( www.RealTimeShredding.com ) to manufacture the machines and pursue the kiosk shredding business opportunities.

The original controller design was done using combinational logic and 7-segment LED displays. It quickly became obvious that this type of controller would work but it would be very costly to change the hardware every time an improvement was introduced. The controller would need to be programmable and allow software updates in the field. And it would have to be cost effective and easy to manufacture if it was going to be a successful product.

To meet the design goals it would need to have considerable complexity and intelligence. Many vending machines and kiosks utilize PC-based controllers and flat panel LCD monitors. This solution was discarded early on because of the cost and space required by these devices.

It was decided that a custom microcontroller-based system would allow maximum flexibility and cost effectiveness. The microcontroller selected would have sufficient I/O and integrated LCD interface capability. It was also field-programmable and much less expensive than off-the-shelf systems. The program loaded could be carefully tailored for the desired behavior and proprietary to the kiosk design.

It was also decided that the high-current, reversible motor required a separate PC board mounted on the multi-horsepower shredding mechanism. This would not only allow precise control of the power to the motor and direction but facilitate the ability to monitor motor current. It can also sense when the bin is full and the motor thermal overload switch is activated. All of these conditions are reported to the main microcontroller so that appropriate action can be taken.

In order to enable this kiosk to be placed unattended in public locations several criteria must be met. First it must be safe; all electronics and moving parts must be completely inaccessible to the user. This was accomplished by putting all of the components in a lockable, heavy duty metal enclosure with a small feed slot 9 inches above the cutting blades. Second it must not be difficult for a user to shred multiple items such as paper, envelopes, paper clips, floppy disks, CD-ROMs, and DVDs without frequent jams or stalls.

The first attempt at preventing jams involved the use of an analog computer to detect and resolve jams. It had limited success but the sophistication required to dynamically sense and prevent jams became a science. After many tests and experiments a digital board utilizing an additional microcontroller proved to be a highly successful solution. Not only could we sense the load on the motor dynamically but we could precisely apply the correct power and direction to the motor and mitigate almost all jams. When the kiosk was first introduced with the analog controller several calls a week were received from users experiencing jams. Since the digital control system was integrated very few jams have been reported and most of them are a result of the input slot being blocked.

The kiosk itself has multiple user interfaces which allow maximum flexibility for different types of customers. A keypad allows the entry of reusable codes for corporate users and the ability to perform system parameter checks and configuration. The bill acceptor will take any US (and some foreign) denominations from 1$ to $20 and can be updated for new bills. A magnetic card reader can be used for all charge cards as well as custom magnetic cards that can be tailored to each customer’s needs.

A serial connection allows a more sophisticated interface for remote configuration and extraction of transaction data. The serial interface also allows the connection of an RF modem so the kiosk can be configured and data extracted remotely. The controller also has connections available for a coin acceptor and Smart Card reader.

I designed the hardware and software for the controller and motor control to be flexible enough to meet many future enhancements. The controller has very limited memory and no hard drive yet it allows for thousands of unique codes for multiple usage and one-time codes for promotional purposes.

This shredding kiosk has gone through numerous design improvements, mechanical and electronic and UL listed. It is a unique product that may revolutionize the way Americans shred documents and other information storage to help prevent identity theft.