摘要:
The invention relates to servo-driven computer-numerically-controlled systems of the type adapted to receive part program instructions defining a desired path of relative movement between a tool and a workpiece, wherein the path may include an interior or exterior curved portion to be effected by coordinated linear movement of machine members along at least two orthogonal linear axes. The invention provides apparati and methods for correcting path radius errors to facilitate rapid and accurate movement along the curve. In a preferred embodiment, such path radius correction is applied to a fixed cycle for machining inside circles preferably incorporating such path radius correction and providing substantially tangential engagement between the tool and a machining locus orbited by the tool to avoid abrupt accelerations or decelerations while the tool is in contact with the workpiece. In addition to avoiding surface blemishes, this facilitates machining a broader range of hole sizes with a given sized tool thereby reducing the need for frequent tool changes. The invention carries out path radius correction by generating position commands received by the servo using corrected radius data, the difference between which and the desired radius to be machined compensates for at least a portion of the path radius error that would otherwise be generated by the servo. Apparatus and methods for threading holes using a non-helical threading tools with or without path radius correction are also disclosed.
摘要:
Interface circuits for electromagnetic position transducers are provided to reduce the effects of capacitive coupling occurring in the conductive cabling between the position transducers and the associated interfaces located remotely therefrom. Capacitive coupling of excitation signals to the transducer output signals result in error signals appearing as cyclic error in measured positions. The magnitude of the coupled signals are substantially reduced by providing excitation signals symmetrical with respect to ground. The magnitude of the coupled signals are also reduced by presenting equal impedances relative to ground to the output signal return and signal paths. By reducing the effects of capacitively coupled signals, conducting cables for the excitation signals and the transducer output signals may be incorporated in a single shielded cable.
摘要:
Positioning errors of a moveable machine member are reduced by compensation for cyclic errors attributable to anomalies of a position transducer. Compensation values are produced which are unique only within the pitch of transducer measurement and are applied to correct the representation of measured position produced by the transducer. Positioning errors not attributable to the position transducer are corrected by compensation of position commands using compensation values associated with fixed calibration points. Use of both compensations is effective to eliminate residual errors in position correction which arise from use of calibration data created without correction of transducer cyclic errors.
摘要:
A method and apparatus for machine member motion control are provided which reduce position path errors in sampled data motion control systems. Position commands defining locations of a moveable machine member are periodically produced at a predetermined interval as is conventional in sampled data motion control. Intermediate position commands are produced at a predetermined sub-interval less than the predetermined interval in response to a parametric function relating member position and time, the parametric function being continuous through positions defined by the position commands. The intermediate position coordinates are computed as the sum of products of coefficients and coordinates of selected member position commands. To reduce processing time, the coefficients are computed and stored in advance of execution of motion for recall as motion progresses. Where a parabolic function is used to produce intermediate position commands, the sum of products of coefficients and, respectively, past, present and target coordinates are used to compute intermediate positions between the present and target positions.
摘要:
An apparatus and method for controlling brushless DC motors are provided. Velocity loop control is performed digitally to produce current commands at a high frequency loop closure interval. Commutation of field coil current is controlled in response to current commutation pattern control signals produced in response to measured relative position of the motor rotor and motor stator and a velocity average over a number of loop closure intervals. Switch control signals to control transistor switches providing current from a DC power source to the motor terminals are produced in response to the current commands, measured motor current and the commutation pattern control signals. The velocity loop control implements a selected transfer function relating velocity, the motor torque constant, and the moment of inertia of the motor and associated load. Facilities are provided for periodically adjusting velocity loop transfer function gain factors and the effective moment of inertia in response to input signals. Additionally, current loop amplification gain factors and time constants are made selectable by input signals.
摘要:
A drive circuit is provided for controlling the energization of a DC motor as a function of speed to maintain the motor speed equal to a speed defined by a speed command signal. The speed command signal is summed with a velocity feedback signal to produce a speed error signal which is used as an input to a motor drive circuit. In accordance with the invention, the speed error signal is limited in order to continuously limit the current through the motor to a continuously changing maximum depending on the speed of the motor. During an initial part of the speed range, the limiting level is increased to maintain a constant maximum motor current. During an intermediate speed range, the limiting level decreases so as to sharply decrease current with increasing motor speed; and during a final speed range, the limiting level increases so as to gradually decrease current with increasing motor speed.