When performing machine tool setup and maintenance operations, it is frequently necessary to use a position transducer to “sweep” a surface and establish its relationship to a machine. A machine operator or maintenance technician typically attaches a position indicator to one portion of a machine, and then sweeps the position transducer over the object of interest, while observing the indicator run-out. If necessary, multiple adjustments and re-checks are made to the position of the object to obtain the desired alignment condition.
Similarly, when machining a work-piece, it is frequently necessary to place the part in position in relation to a fixture or a reference location, such as the center or plane of rotation of a spindle. A conventional approach is for a machine operator to manually measure the misalignment of the part, and then move it into the correct position using a series of incremental steps. When a workpiece is being aligned on a spindle, the machine operator rotates the spindle while measuring the part run-out with a position transducer, and taps the part with a mallet to correct any misalignment. If non-figure-of-revolution surfaces are being aligned, then the machine's linear axes are used to sweep the surface into alignment.
While the above operations may be done accurately in an open machining environment, they may be very difficult and time-consuming when access to the workpiece is constrained by the machine size, or when the machine is enclosed in a glovebox. In such a situation, the machine operator has limited visibility, and manual alignment operations are difficult to perform, especially when done at arm's length.
During the fabrication of a two-sided part, for example, precision alignment is needed to align features on one side with features on the other side. In a limited-access, limited-visibility situation, the alignment operation must measure part run-out with a displacement gauge, then tap the part with a plastic or rubber hammer, repeating until the run-out is acceptably small. Automating the centering operation would advantageously reduce the over-all human effort required, and produce more accurate and repeatable positioning.
A system for automatically aligning a workpiece on a machine tool spindle or the like utilizes a machine-mounted probe to measure the position of the workpiece, and an actuator to tap the workpiece into a desired location based on the position measurement. This transducer-actuator system combines these two functions into a single, self-contained assembly or device that may be mounted on a machine tool turret, a tool-changer magazine, a bracket with a magnetic base, or another machine element.
The part tapper uses a linear actuator to tap the workpiece into the desired location; however, it is an open-loop device with no position measurement transducer associated with the location of the actuator shaft. The transducer-actuator system adds a position transducer to the actuator assembly, and incorporates a computer-based user interface so that the device can be used as a position measurement system by lightly contacting the part surface and recording the contact location, or as an actuator by contacting with enough force to move the part to a desired location.
The system may be used to perform automatic alignment of a part on a spindle by first attaching the transducer-actuator to a machine's boring bar, turret, or other appropriate element. Then the actuator is moved within range of the part surface, while the spindle is being rotated by the machine tool control system at a pre-selected speed. The transducer-actuator controller uses the pre-selected speed and/or the angular position of the spindle to determine when to activate a measurement cycle that lightly contacts the workpiece as it is rotating and determine the misalignment between the part and spindle. The controller then calculates the amplitude and location of alignment taps required to correctly align the part, and commands the actuator to execute these taps as the spindle continues to rotate. The transducer-actuator controller may execute multiple measurement/movement cycles, depending on the amplitude of the initial part misalignment and the desired degree of alignment accuracy. If the desired alignment accuracy is not achieved in a preset number of cycles, then the controller halts the alignment process and outputs a status signal.
The overall alignment cycle may be initiated from a computer-based user interface or from the machine tool control system via a command to the transducer-actuator controller that originates from either the part program or the machine operator. When the transducer-actuator controller completes the alignment process, it outputs a signal that indicates that it is appropriate to continue the manufacturing process. This measurement/alignment process may also be applied to a surface that is not a figure of revolution. In this instance, the machine axes are used to sweep the tapper-actuator past the surface of interest during the measurement and relocation operations.