Electricity: motive power systems – Positional servo systems – Digital or numerical systems
Patent
1987-07-30
1989-04-18
Roskoski, Bernard
Electricity: motive power systems
Positional servo systems
Digital or numerical systems
51 34C, 5116593, G05B 1929
Patent
active
048230618
DESCRIPTION:
BRIEF SUMMARY
The invention relates to stone expansion control for a honing machine. Honing machines are used for fine-finishing cylindrical bores in work-pieces such as automobile cylinder blocks and hydraulic and pneumatic components of all kinds.
In general, a honing machine has a rotatable spindle which carries at its end abrasive stones mounted in carriers which may be expanded radially. In a honing operation the spindle enters the bore in the work-piece and is rotated as the work-piece and spindle are reciprocated with respect to each other. Radial pressure is applied to urge the stones against the wall of the bore.
When the stones are introduced into the bore they must be in a radially retracted position. The stones are then expanded radially at an approach rate to approach the wall of the bore. Honing commences and as the stones remove material from the work-piece they are fed radially outwardly at a honing feed rate until the required bore size has been reached, whereupon the stones are retracted, ready for the next work-piece.
It is desirable to control accurately the stone pressure during honing and also the approach and feed rates. Hitherto, stone expansion drive means have included hydraulic motors or pistons. Examples of such arrangements are described in British patent specification No: 2111876 and European patent specification No: 0063983. Such systems are not satisfactory for high precision control because in practice there are variations in the properties of the drive system and particularly the thermal properties of the hydraulic fluid which seriously affect positional accuracy. These problems are exacerbated by the requirement to supply hydraulic fluid through a rapidly rotating gland.
For the above reasons, electric motor drive for the stone expansion system is better. Such a system is described in U.S. Pat. No. 4,528,776. Here a d.c. motor is controlled in speed by a control input. With such an arrangement, however, the operator has no control over the torque of the motor except to set a cut-out level. It is desirable for the operator to be able to control both the torque (and thus the stone pressure) and the speed. The present invention provides an improved stone expansion system.
According to one aspect of the invention there is provided a stone expansion system for a honing machine which has honing stones mounted to expand radially with respect to a spindle of the machine; a stone expansion drive motor and a stone expansion drive linkage coupling the motor to the stones, the motor being a d.c. electric motor, the stone expansion system being characterised in that there is provided a constant-current amplifier connected to drive the motor; a torque control system whereby the operator can set a torque command input to determine the amplitude of the current from the constant-current amplifier; and a speed control system whereby the operator can set at least one speed command input to determine the speed of the motor, the arrangement being such that the speed control system is effective to ensure control of speed as the stones approach the wall of the bore and that the torque control system is effective to control stone pressure during honing.
There are two ways of controlling a d.c. motor: by controlling the driving voltage or by controlling the driving current. If the driving voltage is controlled then motor speed and current will vary with load and the motor torque will vary to meet the load demanded. The torque delivered will therefore not be controlled. In a stone expansion system the stone pressure will therefore not be controllable by the operator.
If, on the other hand, the driving current is controlled, as by, for example, control of a constant-current amplifier connected to drive the motor, then torque will be controlled but motor speed will not. In a stone expansion system it is particularly important to control the expansion speed as the stones approach the wall of the bore being honed. If the stones are moving too rapidly radially when they meet the wall of the bore the inertial energy
REFERENCES:
patent: 3126672 (1964-03-01), Calvert et al.
patent: 3404490 (1968-10-01), Estabrook
patent: 4455789 (1984-06-01), Gehring
patent: 4679357 (1987-07-01), Richter et al.
Bassirat Hamid R.
Boulton Michael A.
Roberts Joseph I.
Bergmann Saul M.
Delapena Honing Equipment Limited
Roskoski Bernard
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