Industrial robot drive systems can be classified into three main categories based on their power source: hydraulic, pneumatic, and electric. Each of these three basic drive systems has its own characteristics, and in practical applications, they can be combined into composite drive systems as needed.
Hydraulic drive system
Hydraulic technology is a relatively mature technology, characterized by high power, a large force (or torque) to inertia ratio, rapid response, and ease of direct drive implementation. It is suitable for application in robots with high load-bearing capacity, high inertia, and those operating in weld-proof environments.
However, hydraulic systems require energy conversion (electrical energy to hydraulic energy), and speed control often uses throttling, resulting in lower efficiency compared to electric drive systems. Hydraulic systems also cause environmental pollution due to liquid sludge discharge and generate higher operating noise. Because of these drawbacks, hydraulic systems have often been replaced by electric systems in robots with load capacities below 100kg in recent years.
pneumatic drive system
Pneumatic drive systems are characterized by high speed, simple system structure, convenient maintenance, and low price. They are suitable for use in robots with medium to small loads. However, due to the difficulty in implementing servo control, they are mostly used in program-controlled robots, such as loading/unloading and stamping robots.
electric drive system
Due to the widespread use of low-inertia, high-torque AC and DC servo motors and their matching servo drives (AC frequency converters, DC pulse width modulators), this type of drive system is widely used in robots. These systems require no energy conversion, are easy to use, and offer flexible control. Most motors require a precision transmission mechanism. DC brushed motors cannot be used directly in explosion-proof environments, and their cost is higher than hydraulic and pneumatic drive systems. However, because of their significant advantages, this type of drive system is widely used in robots.
Selection principles
The design of industrial robot drive systems needs to focus on four aspects: control method, operating environment requirements, cost-effectiveness, and machine operation speed. The selection principles for commonly used robots are as follows.
1. For material handling (including loading and unloading) and stamping, a limited-point control programmable robot can be used. For low-speed, heavy-load applications, a hydraulic drive system can be selected; for medium-load applications, an electric drive system can be selected; and for light-load, high-speed applications, a pneumatic drive system can be selected. Stamping robots mostly use pneumatic drive systems.
For spot welding, arc welding, and spraying robots, those requiring only arbitrary point and continuous trajectory control need to use electro-hydraulic or electric servo drive systems. For robots requiring higher control precision, electric servo drive systems are more commonly used; heavy-duty handling and explosion-proof spraying robots employ electro-hydraulic servo control.
2. Spray painting robots, due to the need for explosion-proof working environments, mostly adopt electro-hydraulic servo drive systems and intrinsically safe explosion-proof AC electric servo drive systems.
For special robots such as underwater robots, nuclear industry robots, space robots, robots operating in flammable and explosive environments, and robots operating in radioactive environments, AC servo drives are more appropriate.
3. For assembly robots requiring high point repeatability and high running speed (≤4.5m/s), AC, DC, or stepper motor servo systems can be used; if even higher speed and accuracy requirements are needed, a DC servo drive system should be used.
