Tham khảo tài liệu 'mcgraw-hill - robot mechanisms and mechanical devices illustrated - 2003 part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Chapter 2 Indirect Power Transfer Devices 89 Internal gears have teeth on the inside surface of a cylinder. Spur gears are cylindrical gears with teeth that are straight and parallel to the axis of rotation. They are used to transmit motion between parallel shafts. Rack gears have teeth on a flat rather than a curved surface that provide straight-line rather than rotary motion. Helical gears have a cylindrical shape but their teeth are set at an angle to the axis. They are capable of smoother and quieter action than spur gears. When their axes are parallel they are called parallel helical gears and when they are at right angles they are called helical gears. Herringbone and worm gears are based on helical gear geometry. Herringbone gears are double helical gears with both right-hand and left-hand helix angles side by side across the face of the gear. This geometry neutralizes axial thrust from helical teeth. Worm gears are crossed-axis helical gears in which the helix angle of one of the gears the worm has a high helix angle resembling a screw. Pinions are the smaller of two mating gears the larger one is called the gear or wheel. Bevel gears have teeth on a conical surface that mate on axes that intersect typically at right angles. They are used in applications where there are right angles between input and output shafts. This class of gears includes the most common straight and spiral bevel as well as the miter and hypoid. Straight bevel gears are the simplest bevel gears. Their straight teeth produce instantaneous line contact when they mate. These gears provide moderate torque transmission but they are not as smooth running or quiet as spiral bevel gears because the straight teeth engage with full-line contact. They permit medium load capacity. Spiral bevel gears have curved oblique teeth. The spiral angle of curvature with respect to the gear axis permits substantial tooth overlap. Consequently teeth engage gradually and at least two teeth are in contact at .
