Abstract: A polishing pad is used when a surface of a glass workpiece is polished for manufacturing a glass substrate of information recording medium. The polishing pad has a nap layer. The nap layer includes an inner layer that contains a plurality of closed cells, and an outer layer. A plurality of pores are formed on the surface of the outer layer. The sizes of the pores are minute compared to those of the closed cells.

Abstract: An inverter that supplies a desired primary voltage (v1) to an induction motor, a current detector that detects a primary current (i1) from the inverter to the induction motor, a voltage designation value calculating unit that generates a voltage designation value (v1*) for generating the voltage v1, an idling-time speed estimating unit that calculates an estimate value (?r#) of the rotation speed when the induction motor is idling, and a sequence circuit that commands the operations of these units are provided. The idling-time speed estimating unit switches a method for deriving the estimate value on the basis of a current value in the case where a short circuit is generated between windings when the induction motor is idling.

Abstract: A polishing pad used for precise polishing of the surface of a lapped glass workpiece when a glass substrate for use in data recording media is manufactured from a glass workpiece. The polishing pad comprises a base and a polishing portion laminated on the base and contacting the surface of the glass workpiece at the time of polishing. The polishing portion is formed of a foam made of a synthetic resin having a 100% modulus of 11.8 MPa or less. A type of parameter representing the surface roughness of the polishing portion, namely, the maximum height (Rmax), is 70 ?m or less.

Abstract: A polishing pad used for precise polishing of the surface of a lapped glass workpiece when a glass substrate for use in data recording media is manufactured from a glass workpiece. The polishing pad comprises a base and a polishing portion laminated on the base and contacting the surface of the glass workpiece at the time of polishing. The polishing portion is formed of a foam made of a synthetic resin having a 100% modulus of 11.8 MPa or less. A type of parameter representing the surface roughness of the polishing portion, namely, the maximum height (Rmax), is 70 ?m or less.

Abstract: A polishing pad used for precise polishing of the surface of a lapped glass workpiece when a glass substrate for use in data recording media is manufactured from a glass workpiece. The polishing pad comprises a base and a polishing portion laminated on the base and contacting the surface of the glass workpiece at the time of polishing. The polishing portion is formed of a foam made of a synthetic resin having a 100% modulus of 11.8 MPa or less. A type of parameter representing the surface roughness of the polishing portion, namely, the maximum height (Rmax), is 70 ?m or less.

Abstract: A glass substrate for a data recording medium is manufactured by using a tabular carrier with circular holes formed therein, housing disk-shaped glass workpieces in the circular holes of this carrier, sliding polishing pads over the surface of the carrier and the principal surfaces of the glass workpieces and polishing the glass workpieces until the height (NRa) of micro-waviness on the principal surfaces of the glass workpieces is reduced to a predetermined value or less. The height (NRa) of micro-waviness of the principal surfaces is a value dependent on the surface roughness of the polishing pad and the surface roughness of this polishing pad is a value dependent on the surface roughness of the carrier. A glass substrate for a data recording medium is manufactured by reducing the surface roughness (Ra) of the carrier to 0.

Abstract: A glass substrate for a data recording medium is manufactured by using a tabular carrier with circular holes formed therein, housing disk-shaped glass workpieces in the circular holes of this carrier, sliding polishing pads over the surface of the carrier and the principal surfaces of the glass workpieces and polishing the glass workpieces until the height (NRa) of micro-waviness on the principal surfaces of the glass workpieces is reduced to a predetermined value or less. The height (NRa) of micro-waviness of the principal surfaces is a value dependent on the surface roughness of the polishing pad and the surface roughness of this polishing pad is a value dependent on the surface roughness of the carrier. A glass substrate for a data recording medium is manufactured by reducing the surface roughness (Ra) of the carrier to 0.

Abstract: A polishing pad used for precise polishing of the surface of a lapped glass workpiece when a glass substrate for use in data recording media is manufactured from a glass workpiece. The polishing pad comprises a base and a polishing portion laminated on the base and contacting the surface of the glass workpiece at the time of polishing. The polishing portion is formed of a foam made of a synthetic resin having a 100% modulus of 11.8 MPa or less. A type of parameter representing the surface roughness of the polishing portion, namely, the maximum height (Rmax), is 70 &mgr;m or less.

Abstract: A polishing pad is used when a surface of a glass workpiece is polished for manufacturing a glass substrate of information recording medium. The polishing pad has a nap layer. The nap layer includes an inner layer that contains a plurality of closed cells, and an outer layer. A plurality of pores are formed on the surface of the outer layer. The sizes of the pores are minute compared to those of the closed cells.

Abstract: The present invention provides a variable-speed controlling device for use with an induction motor, which includes a means for compensating for the discrepancy between a secondary magnetic flux instruction value and a secondary magnetic flux actually occurring in an induction motor, realizes a satisfactory control by generating the secondary magnetic flux according to the instruction value, and can generate desired torque and improve a motor efficiency. The variable-speed controlling device according to the present invention, for use with an induction motor, includes a voltage instruction value calculating unit, an integrating unit, a power converting circuit, a current detecting unit, an induced voltage calculating unit, a position discrepancy amount calculating unit, and a compensating unit.

Abstract: A control apparatus for estimating the flux, the current, and the speed of an AC motor using the current and the voltage, and controlling the vector of an AC motor using the estimated speed, a flux command, and a torque current command. The speed is estimated by adding a product of the deviation between the actual value and the estimated value of a magnetization current, the level of a torque current correspondence value, the sign correspondence value of a primary frequency command value, and a gain to an outer product of an estimated current deviation and an estimated flux. Thus, a stable speed estimating operation can be performed to successfully operate the motor in a low speed area in which a voltage frequency applied to the motor is extremely low.

Abstract: The apparatus calculates a torque that an induction motor generates while considering an iron loss even in a boosting state for exceeding the rated excitation. The calculation is based on a reference voltage value fed to an inverter for driving the induction motor, a q-axis current component and a d-axis current component resolved from a detected current of the induction motor on a rotating coordinate system, a primary resistance of the induction motor and a primary angular frequency. The apparatus includes an iron loss calculator that calculates the iron loss of the induction motor based on hysteresis characteristics of the stator core, a divider that divides the calculated iron loss by the primary angular frequency and an adder that calculates the generated torque by subtracting the result of the division from the torque calculated without considering the iron loss.

Abstract: A control apparatus for estimating the flux, the current, and the speed of an AC motor using the current and the voltage, and controlling the vector of an AC motor using the estimated speed, a flux command, and a torque current command. The speed is estimated by adding a product of the deviation between the actual value and the estimated value of a magnetization current, the level of a torque current correspondence value, the sign correspondence value of a primary frequency command value, and a gain to an outer product of an estimated current deviation and an estimated flux. Thus, a stable speed estimating operation can be performed to successfully operate the motor in a low speed area in which a voltage frequency applied to the motor is extremely low.

Abstract: A control apparatus for an induction motor includes a current detector for detecting the current of the induction motor; a first coordinate transformer for resolving the current into an exciting current component and a load current component; a slip value calculator for calculating a slip angular frequency of the induction motor based on the load current component; a correction value calculator for calculating a correction value for the slip angular frequency of the induction motor in response to the change of the exciting current component; a multiplier for correcting the slip angular frequency by using the correction value calculated in the correction value calculator; an adder for calculating a reference primary angular frequency based on the corrected slip angular frequency; a voltage vector calculator for calculating a reference voltage value based on the reference primary angular frequency; and a second coordinate transformer for feeding the calculated reference voltage value to the inverter.

Abstract: When an induction motor is variable-speed-controlled via an electric power converting circuit, the magnetic flux of the induction motor is modulated by adding an alternating current signal to, for example, a magnetizing current command. For example, the component depending on the slip frequency of the induction motor is extracted by an extracting means from at least one of the amounts of changes of the voltage, the electric current, and the magnetic flux, which are caused by the modulation of the magnetic flux. The amount of the voltage or the electric current supplied to the motor, etc. is controlled based on the extracted component via an adjusting unit and a control means, thereby implementing superior control of the induction motor.

Abstract: A variable-speed control apparatus computes the leakage inductance of an AC motor, correctly compensates the leakage inductance, and controls the variable speed of the AC motor. The variable-speed control apparatus has an AC signal generation circuit for generating an AC signal, and obtains a leakage inductance calculation value of the AC motor based on the AC signal and the measured actual current value. The differential value of the summation of a current command value and the AC signal is multiplied by the leakage inductance calculation value to generate a signal for use in compensating the voltage drop caused by the leakage inductance, and added to a voltage command value to cancel the deviation between the actual current value and the M-axis current command value and to obtain the second voltage command value. The second voltage command value is converted into a 3-phase voltage command value and used in controlling the AC motor, and the voltage drop caused by the leakage inductance can be compensated.

Abstract: To provide a trans-vector controller for an alternating current ("AC") motor that facilitates operating the secondary resistance of the AC motor without experimentally rotating the AC motor.In a preferred embodiment, the variable speed control circuit, including a secondary resistance value generating device, changes the direct current ("DC") exciting current and operates the secondary resistance of an induction motor by superimposing an AC signal with small amplitude outputted from a AC signal generator onto a reference current value immediately before the start of the induction motor in the state of DC excitation.

Abstract: A variable speed controller for an induction motor that estimates the primary angular frequency and the speed without causing any error in the drive region where the induced voltage is low. The primary angular frequency and speed estimating device includes: a changeover signal generator that generates a changeover signal indicative of a first mode of operation when the induced voltage is greater than the changeover threshold, and a second mode of operation when the induced voltage is less than the changeover threshold; a differentiator, filter, etc.

Abstract: A control apparatus for conducting a variable speed control of an AC motor by controlling an M-axis component and a T-axis component of a current flowing through the AC motor.

Abstract: Disclosed are methods and apparatus for quickly measuring a primary resistance value of an AC motor without using high precision detectors and detecting malfunctions such as breaking of wire in the AC motor or in a power converting mechanism, open phase, and three-phase unbalance. A voltage drop attributable to the primary resistance of the AC motor can be estimated by using an estimated resistance value R.sub.1.sup.#, which is estimated in turn by an integral or proportional-plus-integral operation on the deviation between a detected magnetizing current value I.sub.M and a reference magnetizing current value I.sub.M *, in place of an actual primary resistance value R.sub.1. The time for the estimated resistance value R.sub.1.sup.# to reach the true primary resistance value is reduced with a varying reference magnetizing current value I.sub.M **. Variations of the estimated primary resistance values R.sub.1.sup.# s between the phases are corrected with a mean estimated primary resistance value R.sub.1M.sup.