| 摘要 |
<p>An electrohydraulic system for bending tube stock (22) includes a bend head (12) having a mandrel (14) and an actuator (18) coupled to a bending die (16) for engaging the tube stock and bending the stock around the mandrel. A clamp (28) is coupled to a second actuator (32) for gripping the tube stock, and a third actuator mechanism in the form of a boost cylinder (40) is coupled to the clamp for urging the tube stock lengthwise into the bend head. An electrohydraulic valve (46) is responsive to an electronic valve control signal (U) for variably feeding hydraulic fluid to the boost cylinder, and velocity of slip at the clamp is determined. An input pressure command signal (PC) is compared with pressure at the boost cylinder to develop a pressure error signal. Slip velocity (V) is compared with a velocity limit command (Vl) to develop a velocity difference when slip velocity exceeds the velocity limit, and the pressure error signal (Ep) is modulated and employed as the valve command signal to maintain slip velocity at or below the level of the velocity limit command.</p> |
