Electricity: motive power systems – Open-loop stepping motor control systems
Patent
1996-02-29
1998-12-08
Martin, David S.
Electricity: motive power systems
Open-loop stepping motor control systems
116 47, 116297, H02P 800
Patent
active
058475311
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a process for reducing the strength of an uncontrolled pointer movement.
BACKGROUND INFORMATION
The essay, "Der Schrittmotor und seine Schrittdauer" (The Stepper Motor and its Step Pulse Duration), Feinwerktechnik & Me.beta.technik (Precision Engineering and Metrology) 99 (1991)7-8, pp. 327-332, by Klaus Mayer, discusses a stepper motor which has a permanent-magnetic rotor that is mounted on a motor axle and rotates within the rotating magnetic field of two coil systems. When a pointer is installed on the axle of the rotor, a specific angle of rotation can be adjusted by driving the stepper motor, and the angle of rotation can be indicated by the pointer over a dial. Such systems can be used, e.g., for displaying the rotational speed, velocity, and other vehicle-specific information in a motor-vehicle combination instrument. It is customary to provide a stop pin at the lower end of the scale as a mechanical stop for the pointer and, in particular, immediately after turning on the stepper motor, to drive the pointer against this stop means to obtain a defined initial position for the rotor of the stepper motor. When working with conventional stepper motors under the state of the art, the problem often occurs that the system comprised of the pointer and the stepper motor, it being possible to mount a speed-transforming gear between the pointer and the rotor, is mechanically strained, because when the mechanical components press against the stop means, they are elastically deformed by the rotor torque (rotation means). The cause of such deformations lies, above all, in the elasticity of the pointer and in the mechanical play of the speed-transforming gear. If the stepper motor is switched off after the stop means is hit, often the restraint (torque bias) of the system is abruptly released, so that the pointer jumps away from the stop means. The uncontrolled springing of the pointer off of the stop means can result in display errors. Also, subjectively, the person steering the vehicle usually perceives a pointer springing suddenly away from the stop means as an unpleasant sensation.
SUMMARY OF THE INVENTION
In contrast, the advantage of the process according to the present invention is that the strength (intensity) of such an uncontrolled pointer movement is reduced. The strength is understood to be the expected angle of rotation of the pointer when it jumps off of the mechanical stop means. As a result, one attains the advantage that the pointer driven by the stepper motor is situated at an exactly defined position even after a shut-off operation, so that the accuracy of the display and, thus, its readability is improved. Moreover, there is an improvement in the subjective perception of the pointer movement by the person reading the dial.
When the field strength is lowered, there is the further advantage that the process for reducing the strength of an uncontrolled pointer movement is able to be realized quite simply and cost-effectively, because the magnetic field strength of the drive coils is lowered.
The pointer movement has the advantage that because of the controlled rotation of the pointer away from the stop means, there can be no free rotation of the rotor by more than the minimum step angle, so that an especially smooth rotational performance of the rotor and, thus, of the pointer is attained.
The advantage of repeatedly switching on after switching off is that an especially simple driving of the stepper motor results from the principle of alternating switch-on and switch-off operations, which makes it possible to achieve a controlled interception (capture) of the rotor following the pointer moment of rotation to reduce the strength of the uncontrolled pointer movement.
By continuously lowering the field strength of the magnetic field of the drive coils, a very uniform rotor performance is produced and, thus, the torque acting on the pointer is relieved very uniformly, since the rotor moves in an especially jerk-free manner during the pro
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K. Mayer, "Der Schrittmotor and Seine Schrittdauer", Feinwerktechnik & Messtechnik 99, pp. 7-8, 1991.
Herzog Bernhard
Hoffsommer Klaus
Steger Roland
Martin David S.
Moto Meter GmbH
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