1. An AC drive for providing power to a motor, comprising:
an enclosure,
a temperature sensor for measuring temperature within the enclosure,
a heater resistor within the enclosure,
a rectifier for rectifying AC power and producing DC power on a DC link,
an inverter connected to the rectifier across the DC link and converting DC power to adjustable frequency power,
a capacitor across the DC link,
a switch in series with the resistor across the DC link, and
a controller operable to monitor the temperature and voltage across the DC link and control the switch to provide power to the resistor if the motor is inactive and the sensed temperature is below a predetermined setpoint.
2. The apparatus of claim 1 further including a separate dynamic brake resistor for dissipating energy upon braking of the motor and a second switch in series with the dynamic brake resistor and connected across the DC link, and wherein the controller independently controls both switches.
3. The apparatus of claim 1 further including a separate dynamic brake resistor for dissipating energy upon braking of the motor and a second switch under the control of the controller for selectively coupling either resistor in series with the first switch.
4. The apparatus of claim 1 wherein the switch is a transistor of the inverter.
5. The apparatus of claim 1 wherein the switch is a controllable switching device selected from the group including a relay, an SCR, a GTO, a GCT and an IGBT.
6. The apparatus of claim 1 further including a heat sink fan that remains off when the sensed temperature is below the predetermined setpoint and power is provided to the heater resistor.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A head-mounted stereoscopic display, comprising:
a head-mounted base unit;
a single display unit arranged on the side facing away from human face inside the head-mounted base unit for presenting images to human eyes;
an optical magnifying lens arranged on the side near human face inside the head-mounted base unit; and
an annular headband connected with the head-mounted base unit and extending around user’s head for fixing the head-mounted base unit;
wherein the head-mounted base unit comprises a face-mask unit and an optical base unit, the face-mask unit fits with the human face tightly, and the optical base unit fixes the display unit and the optical magnifying lens, and
wherein the single display unit displays two different images for human’s left and right eyes respectively side by side simultaneously.
2. The head-mounted stereoscopic display as claimed in claim 1, further comprising an image height-compressing lens, arranged on the side near the display unit inside the head-mounted base unit, for compressing the height of the images as displayed to make the images as observed by eyes have a normal aspect ratio.
3. The head-mounted stereoscopic display as claimed in claim 2, wherein the image height-compressing lens is a plane-concave cylindrical lens or double-concave cylindrical lens.
4. The head-mounted stereoscopic display as claimed in claim 3, wherein the concave surface is arc-shape whose curvature radius is \u2153\u02dc\u2155 or \u2154\u02dc\u2153 of the height of the display unit.
5. The head-mounted stereoscopic display as claimed in claim 3, wherein the concave surface is a parabolic surface whose curvature radius on the top in cross section is \u2153\u02dc\u2155 or \u2154\u02dc\u2153 of the height of the display unit.
6. The head-mounted stereoscopic display as claimed in claim 3, wherein the distance between the image height-compressing lens and the display unit is \u2153\u02dc\u2155 of the height of the display unit.
7. The head-mounted stereoscopic display as claimed in claim 1, wherein the distance between the optical magnifying lens and the display unit is above 40 mm, and the focal length of the optical magnifying lens is less than 70 mm.
8. The head-mounted stereoscopic display as claimed in claim 1, wherein the diameter of the optical magnifying lens is more than 40 mm, and the gap between the human eyes and the optical magnifying lens is more than 20 mm to accommodate eyeglasses.
9. The head-mounted stereoscopic display as claimed in claim 1, wherein the optical magnifying lens comprises two optical magnifying lenses which are capable of rotating a certain angle from the vertical state, so that the center distance between the two optical magnifying lens will vary within a range of 60 to 70 mm.
10. The head-mounted stereoscopic display as claimed in claim 1, wherein the face-mask unit and the optical base unit are detachable by any of a structure of rotating snap-fit engagement, rotating magnetic engagement and top sliding-slot engagement.
11. The head-mounted stereoscopic display as claimed in claim 1, wherein the annular headband of the head-mounted base unit goes around above ears of the user, and a bone conduction sound module is provided on the annular headband to receive audio signal from outside and vibrate to spread the audio signal.
12. The head-mounted stereoscopic display as claimed in claim 1,
wherein the face-mask unit of the head-mounted base unit concaves a predetermined depth facing away from the human face side, the concave part is surrounded by a forehead-supporting part supporting on the top of the head, a cheek-supporting part supporting on the lower of the head, a nose-supporting part supporting in the middle of the face, and the annular headband supporting the left and right side of the head, so that the head-mounted base unit is held tightly with the human face; and
a pair of observation windows is further provided in the cheek-supporting part of the head-mounted base unit in the lower part of the head, corresponding to the positions through which the user looks downwards with his left and the right eyes, and the observation windows are covered with a slideable light-blocking cover for the user to block the light as needed.
13. The head-mounted stereoscopic display as claimed in claim 12,
wherein the concave part near the observation window further concaves from the vertical direction toward the inside of the head-mounted base unit and forms a wedge triangle \u201c\u2220\u201d shape together with the cheek-supporting part, in order to provide more observation space below for human eyes to observe through the observation window.
14. The head-mounted stereoscopic display as claimed in claim 12, wherein a sliding slot is provided in the cheek-supporting part, when the light-blocking cover is pushed forward along the sliding slot away from the human face to the end of the slot, the light-blocking cover is opened to reveal the window, and when the light-blocking cover is pushed forward along the sliding slot towards the human face, the light-blocking cover is closed to block the window.
15. The head-mounted stereoscopic display as claimed in claim 12, wherein one end of the light-blocking cover far away from the user is provided with a rotation shaft, while the other end is in a free state,
when the free end of the light-blocking cover is pushed downwards, the light-blocking cover is rotated downwards about 180 degrees and then attached with the cheek-supporting part again, the light-blocking covers is open, and when the free end of the light-blocking cover is rotated in an opposite direction, the light-blocking covers is closed.
16. The head-mounted stereoscopic display as claimed in claim 12, wherein the light-blocking cover is in a louver type.
17. The head-mounted stereoscopic display as claimed in claim 12, wherein the light-blocking cover is provided with a metal or magnetic component which can be engaged with a corresponding metal or magnetic component at the bottom of the head-mounted base unit, so as to be detachable from the head-mounted base unit.
18. The head-mounted stereoscopic display as claimed in claim 1, further comprising clamping components for clamping the display unit in front of the optical magnifying lens away from the human eyes,
wherein the clamping components comprise a first clamping component and a second clamping component arranged in opposite sides to fix an detachable external display unit in place of the display unit in front of the user in position where the user can see the images provided by the external display unit when wearing the head-mounted stereoscopic display.
19. The head-mounted stereoscopic display as claimed in claim 18, wherein the clamping components are rotatable oppositely or reversely within a certain range of angles by spring hinges so as to cover and fold in the front of the optical magnifying lens of the head-mounted base unit in the initial position and to clamp resiliently and fix the external display unit in the operation position.
20. The head-mounted stereoscopic display as claimed in claim 18, wherein the clamping components are provided with one or more slots arranged respectively on the sides facing each other to adjust the distance between the display screen and the human eyes.