Passage 3

In 1995 about 700,000 robots were operating in the industrialized world. Over 500,000 were used in Japan, about 120,000 in Western Europe, and about 60,000 in the United States. Many robot applications are for tasks that are either erous or unpleasant for human beings. In medical laboratories, robots handle potentially erous materials, such as blood or urine samples(尿样). In other cases, robots are used in repetitive, unchangeable tasks in which human performance might degrade over time. Robots can perform these repetitive, high-precision operations 24 hours a day without fatigue. A major user of robots is the automobile industry. General Motors Corporation uses approximately 16,000 robots for tasks such as spot welding(点焊), painting, machine loading, parts transfer, and assembly. Assembly is one of the fastest gnawing industrial applications of robotics. It requires higher precision than welding or painting and depends on low-cost sensor systems and powerful inexpensive computers. Robots are used in electronic assembly where they load microchips on circuit boards. Activities in environments that cause great er to humans, such as locating sunken ships, cleanup of nuclear waste, exploring for underwater mineral deposits, and active volcano exploration, are ideally suited to robots. Similarly, robots can explore distant planets. NASA’s Galileo, an unmanned space probe, traveled to Jupiter in 1996 and performed tasks such as determining the chemical content of the Jovian atmosphere. Robots are being used to assist surgeons in installing artificial hips, and very high-precision robots can help surgeons with delicate operations on the human eye.

In the sentence "Robots can perform these repetitive, high-precision operations 24 hours a day without fatigue." the word "fatigue" can be explained as ______.