Salad bars are magnets for bacteria and viruses. Even if the sprouts and ranch dressing aren't tainted, the serving utensils may be.

The Silicon Valley start-up Chowbotics has devised what it says is a partial solution. Its device, which it calls Sally the Salad Robot, is aimed at reducing the risk of food-borne illness by assembling salads out of precut vegetables stored in refrigerated canisters.

Diners use a touch screen to place their orders, choosing from a menu of recipes or designing their own salads. The machine calculates the number of calories per salad and drops the veggies into a bowl in less than a minute. There is less human contact with the food.

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But as a growing number of food- and drink-slinging robots have begun interacting with diners in the San Francisco Bay Area, Deepak Sekar, the device's inventor and the founder and chief executive of Chowbotics, has faced questions about whether his machine will put people out of work. He denies that that will happen.

Mr. Sekar insists that his company's current focus — which is on the salad bar market instead of restaurants more broadly — means Sally won't be a job killer. He says workers at salad bars could restock the robot, which holds enough ingredients for 50 salads before it needs to be refilled. And he says, restaurants can continue with their usual food preparation methods — relying on kitchen workers to do the chopping or buying precut vegetables.

In offices, the gadget could be a source of new jobs, Mr. Sekar says. "You're going to get fresh food in, and you're actually creating jobs for people who refill the canisters in these offices," he said.

Nonetheless, robot-induced unemployment is a mounting concern. Bill Gates recently made a case for taxing companies that own robots, which could delay their implementation and provide some money to retrain people whose jobs are lost. The San Francisco board of supervisors is considering a so-called robot tax.

"We could be looking at over 50 percent of jobs disappearing in the United States over the next 10 to 15 years," said Jane Kim, a San Francisco supervisor. "And it's not jobs going abroad, or offshoring of jobs. It's robots."

There is evidence that automation can have a devastating effect on employment. Commercial robots have already begun to eliminate jobs, according to an M.I.T.-Boston University study published in March. Researchers analyzed the effects of industrial robots on local labor markets in the United States from 1990 to 2007, and estimated that adding one robot per 1,000 workers has led to unemployment for up to six workers and has caused a decrease in wages by up to 0.50 percent.

Some unions are discussing their own strategies for contending with a robot-clogged future. "It's something our union and many unions are still studying," said Ian Lewis, research director for Unite Here Local 2, a union that represents hotel, food service, restaurant and laundry workers in San Francisco and San Mateo, Calif. "We're absolutely concerned and trying to grapple with it."

Whatever their effect on employment, new robots are on the way. Mr. Sekar, an inventor with a doctorate in electronics and computer engineering, said he came up with the idea of building a kitchen robot while working as director of engineering for a semiconductor company. Although he loved cooking at home, he said he craved a way of reducing the work involved.

"I was spending 90 percent of my time doing something sadly repetitive, like chopping ingredients or stirring," Mr. Sekar said. He wanted to automate those tasks, much as vacuuming can be delegated to Roomba, iRobot's robotic vacuum. Soon, he switched his focus to food-service robots for restaurants and offices.

Mr. Sekar said his robot has the potential to save money for small businesses that install it in office kitchens alongside appliances like coffee machines. Walking a couple of minutes within a building to a salad-tossing robot instead of venturing outside for lunch would mean shorter work breaks and increased productivity, he said. He calls Sally "the smallest and most affordable cafeteria an office can have."

The robot is being tested in the office of the Redwood City, Calif., technology incubator GSVlabs and at Calafia Café and Market A Go-Go, a restaurant in Palo Alto, Calif., with an attached market owned by Charlie Ayers, who is the Chowbotics executive chef.

This fall, Chowbotics will begin fulfilling orders for 10 robots, priced at $30,000 each, Mr. Sekar said. He envisions his robots producing healthy meals in convenience stores, airports, hotels, hospitals and universities. "You're seeing the momentum of Silicon Valley behind it," Mr. Sekar said. So far, Chowbotics has raised $6.3 million in venture funding from various investors.

For recipes, Mr. Sekar turned to Mr. Ayers, the former head chef of Google who also has cooked for members of the Grateful Dead. "There's a lot of passion in what I do creating flavors that will come out of the machines," Mr. Ayers said. For instance, he said he has devised a menu for an office robot that can serve salads with South Asian ingredients.

Still, Mr. Ayers says other chefs have criticized him. "Many of my colleagues in the industry are like, 'What are you doing to us? You're going to the machines?'" said Mr. Ayers.

He responds that he is helping to create jobs because these robots will always need to be filled, maintained and cleaned by people. "There are going to be logistics companies, cleaning companies, service companies, robot repair companies," Mr. Ayers said. "Human interaction with Sally is not going away."

If Chowbotics succeeds with salads, Mr. Sekar hopes to expand to other cuisines and admits that human workers could then be displaced. "We're going to go after other types of food," he said. "It's hard to tell what will happen in the future and how this all might impact jobs."