Controller enables novel power tool safety device

SawStop is now in production with a new power table saw equipped with a revolutionary sensing and instant brake feature enabled by TMS320C2000 digital signal controllers.

Enabling greater safety in the workplace and at home, SawStop is now in production with a new power table saw equipped with a revolutionary sensing and instant brake feature enabled by TMS320C2000 digital signal controllers from Texas Instruments.

Advanced sensing based on TI's leading digital signal processor (DSP) technology detects accidental contact between the blade and a user to completely stop and retract the circular blade in less than 5ms.

As a result, many woodworking accidents will now require only Band-Aids instead of emergency medical care.

The SawStop safety unit places a small charge on a standard saw blade, creating a steady 3V signal on the blade during normal use.

When the blade comes into contact with a user's skin, the capacitance of the human body changes the voltage level on the blade.

The C2000 controller monitoring the blade voltage detects this change within 50us.

The controller then trips a high-speed, high-force, single-use actuator that forces a brake into the teeth of the blade and stops it within 5ms.

This safety module can be replaced easily by the user after it has been used.

The controller also performs self-tests of the module and prevents the saw from starting if it detects a problem with the safety feature.

C2000 controllers are designed for applications like SawStop's, which require the high performance of TI's DSP technology in combination with the peripheral integration and ease-of-use typically found in a microcontroller (MCU).

Leveraging the DSP performance, the TI controller not only enables the SawStop tool to sense blade-to-hand contact almost instantaneously, but also makes the saw "smart" enough to discriminate between flesh and wet or green wood.

The high level of integration inherent in C2000 controllers, including high performance analogue-to-digital convertors (ADCs), helps keep the SawStop safety module small, affordable and easy to replace.

Embedded Flash memory and TI's Code Composer Studio programming environment helped simplify design and speed SawStop product development.

"When we started out, we were unsure how exactly we were going to build the braking module, so we needed flexibility and to take a cost-conscious approach", said Steve Gass, PhD, SawStop President and inventor of the SawStop technology.

"The C2000 digital signal controller offered a level of performance we could not get from an MCU, along with lots of on-chip functionality and reprogramming flexibility for easier development".

"We couldn't find another solution that gave us so much at such an affordable price".

With its invention for blade monitoring and instant braking, SawStop addresses an area of serious concern for power tool users.

In 2003, the US Consumer Product Safety Commission (CPSC) estimated that about 65,000 medically treated injuries in the USA led to roughly $2 billion annually in economic costs.

By SawStop's estimate, the CPSC cost of injuries is actually 10 times greater than the total annual sales value of table saws.

A small increment in unit cost to promote greater saw safety will ultimately result in huge economic savings for end users by reducing the flood of devastating injuries that currently occur on these types of saws.

Cabinet saws by SawStop are currently in production and are targeted mainly for users in schools and industrial shops.

The introduction of a contractor table saw targeted to home hobbyists is slated for the first half of 2005.

In addition to innovative electronic blade monitoring and braking technology, the new saws further promote safety by introducing to the USA a European-style riving knife that stabilises the wood in order to minimise kickback as well as improve dust collection to reduce the hazards associated with wood dust.

The high performance offered by TI digital signal controllers will also support the design and introduction of new features to SawStop products in the future, which may include security features to prevent theft and unauthorised use, digital motor control of saw speed and positioning, monitoring of wood moisture and quieter saw operation.

SawStop plans to license its safety technology to other saw manufacturers for applications such as handheld power saws, bandsaws, radial arm saws, chainsaws, jointers, shapers and other woodworking tools.

In addition, this DSP-enabled technology may be adapted to sewing machines, chippers, trimmers, presses and other machines where motion could endanger an operator.

Back to top