Engineers design and build things every day. But where do you cross the line that divides simply combining existing technologies for their obvious purposes and inventing something really new?

Exactly where you stand in a given situation often depends on whether you already have a relevant patent. Patent owners naturally want their patents to cover as much territory as possible, while would-be inventors want to be restricted as little as possible by someone else’s ­patent monopoly.

Generally speaking, in order to be patentable an invention has to be both new and unobvious. Newness is a fairly easy objective determination: Is the patent applicant laying claim to something never before seen? Unobviousness, though, is thorny, since it necessarily involves a subjective determination, not to mention that it is easy to deem something obvious once it has been explained to you.

Exactly what standard should be used to determine obviousness is currently under the microscope in the United States. The U.S. Supreme Court has agreed to hear a case that could have a profound impact on what is ­patentable. Everyone in patent land is weighing in, including Microsoft, a team of law professors, and the federal government, mostly with arguments that the current standard for unobvious­ness is too low and has resulted in a lot of bad patents’ being issued.

Before we get into the Supreme Court case--which is expected to be decided next year--let me present two controversial inventions and their patents, to illustrate some of the issues in play.

The first example is the Furminator pet-grooming tool (U.S. Patent Nos. 6782846 and 7077076). The blade of the Furminator is, as admitted in the patent, an Oster A5 blade, long used in Sunbeam Corp.’s ­electric hair clippers. Pet groomers often used that same blade, taken out of the ­clipper, to remove shed hair, but the blade was difficult to hold by itself. So the Furminator patents cover the clipper blade positioned in an ”elongate handle ­portion.” Should the idea of adding a handle to Sunbeam’s clipper blade really be patentable? We’ll see. Furminator sued three companies in January, including the home-goods retail chain Linens ’n Things, for selling similar pet-grooming tools.

The second example is a little more complex. Document and image scanners have long included a microcontroller that controls the image sensor, the sheet-feed subsystem, and so on. Traditional scanners also had their own independent power supply. The idea of Syscan’s Patent No. 6275309 is to borrow power from a PC in order to operate the scanner, so that the ­scanner does not have to be plugged into a wall outlet. Computing power is borrowed from the PC as well, so no microcontroller is required in the scanner. How are power and control signals from the PC coupled to the scanner? By a PCMCIA card. A related patent, No. 6459506, also belonging to Syscan, covers a scanner powered and controlled via a USB interface.

Syscan didn’t invent the PCMCIA card, USB, or scanners. Instead, the patentee adopted PCMCIA and USB technology for use in scanners. The result was two patents preventing any other scanner manufacturer from using PCMCIA or USB to power or control their products--even though USB was specifically designed to allow peripheral manufacturers to power their devices from electricity supplied by the USB interface and to be controlled using software running on a connected computer. Syscan is in litigation with one original equipment manufacturer (OEM) and four other scanner companies over the two patents.