Electricity: motive power systems – Limitation of motor load – current – torque or force
Reexamination Certificate
1995-11-13
2001-04-10
Salata, Jonathan (Department: 2837)
Electricity: motive power systems
Limitation of motor load, current, torque or force
C318S466000
Reexamination Certificate
active
06215265
ABSTRACT:
FIELD OF THE INVENTION
The invention pertains to a process for automatically stopping drives which contain electric motors for devices such as roller shutters, rolling gates, jalousies, awnings and movie screens and to a system for implementing this process.
BACKGROUND OF THE INVENTION
In electrically operated devices such as roller shutters, rolling gates, jalousies, awnings, movie screens, etc., the conventional way of setting the desired end positions is to use adjustable mechanical limit stop switching devices. Examples of drives of this type are known from DE No. 3,011,706 C2 and DE No. 4,402,524 C2. In these known drives, the drive shaft of the drive is stopped in an upper and lower end position by means of so-called shaft limit switches. So that shaft limit switches of this type can be adjusted, the switch usually has setting buttons, by means of which the relative position of cam wheels inside the shaft limit switch can be reset. So that the lower end position can be adjusted, the roller shutter, etc., must first be rolled down, and just before it reaches the desired lower end position, the set button responsible for shutting off the motor must be pushed. A similar process is used to set the upper end position of the jalousie.
Shaft limit switches of this type are relatively complicated in their design, and, depending on the location where they are installed, it can often be difficult to adjust them because of difficulty of access. In addition, these known shaft limit switches are unable to protect the roller shutters, etc., from damage as they are rolled up and down. That is, if the roller shutter becomes jammed or blocked as it is rolled up or down, the known shaft limit switches do not shut off the drive because these switches are designed only to turn the drive off at the end position. The drive therefore continues to run and can therefore damage the component being driven and even, in an extreme case, destroy it.
Another problem is the possibility that ice can form on the roller shutter, etc., to be actuated, wherein, for example, it is in its lower end position where it can thus be immobilized. When the electric motor is turned on, it will heat up because of the extreme load, and the thermal safety system will be actuated. The driven component can also be damaged in this case as well.
SUMMARY OF THE INVENTION
The invention provides a process and a system by means of which, regardless of whether shaft limit switches are present or not, the drive can be stopped safely when the roller shutter, etc., reaches its end position. The invention protects both the roller shutter, etc., as well as the drive from damage.
The invention advantageously provides simplicity of design, automatic recognition of end position, reliable protection from damage to the roller shutter, as well as enables connection of electric motors in parallel.
The system and method of the present invention are based essentially on the continuous measurement of the torque of the electric motor after it has been turned on so that the motor can be shut off either when a predefined torque is exceeded or when a predefined change in torque is exceeded.
By monitoring the torque of the electric motor as the roller shutter, etc. is rolled up and down, it is possible to detect both abrupt changes in the torque and torques which exceed a certain maximum value. When the roller shutter, etc., arrives at its upper or lower end position, a change will occur in the torque, which is recognized by a suitable detection device with an associated control unit, and this results in the automatic shut-off of the electric motor. It is also possible, furthermore, to provide stop bars for the roller shutters at the upper and lower end positions, these bars being installed where the roller shutter, etc., is intended to stop. As soon as the roller shutter contacts these stop bars, the torque of the electric motor changes, and this change is detected. Although shaft limit switches can still be used, they are no longer necessary.
In addition, it is ensured by means of the process according to the invention that if the roller shutter, etc., becomes jammed or blocked during its upward or downward progress, that the electric motor will be turned off safely because of the higher torque developed in the electric motor or because of the associated change in the torque. Because of this safety shut-off, the motor is prevented from overheating, and damage to the component being driven by the motor is reliably prevented.
The electric motor is shut off when a certain predefined torque is exceeded, and it is a simple matter to read this maximum torque from a table into the control unit for the motor. The table is stored in a nonvolatile data memory unit of the control unit and is drawn up for the specific type of electric motor being used. The table also takes into account the actual operating voltage of the electric motor, which ensures that the predefined torque is adjusted to the actual operating conditions.
An especially simple way of detecting the load and thus the torque of the electric motor includes evaluating the phase shift of the current flowing through the phase windings of the electric motor. If the electric motor has at least two phase windings and one capacitor, then it is possible to derive the actual torque of the electric motor from the phase shift of the current flowing through these two phase windings. A small phase shift correlates with a heavy load, whereas a large phase shift correlates with a light load and therefore with a small amount of torque on the electric motor.
By monitoring the phase shift between the two motor windings, it is possible to avoid a separate sensor for measuring the speed or torque. As a result, the system for implementing the process according to the invention can be a very simple design.
In an elaboration of the invention, the phase shift between at least two motor windings is detected and stored in memory just after the electric motor has ben turned on. This stored value is continuously updated. That is, after a predefined time interval, which can vary from 100 to 800 msec, an, updated value replaces the old value. The control unit can thus enable turning off the electric motor whenever it detects a predefined, maximum allowable change in the phase shift with respect to the immediately preceding stored phase shift value.
It has been found that detecting the torque of the electric motor is sufficient, especially in the case of heavy roller shutters, rolling gages, etc., to provide a reliable criterion for turning off the electric motor.
Elaborations of the process according to the invention are intended to increase the reliability with which the electric motor is turned off.
For this purpose, it is possible, for example, to monitor the rpm's of the roller shaft on which the roller is mounted and which is connected to the drive by way of a roller shaft coupling. When the speed of the roller shaft falls below a certain defined value, the electric motor is again turned off. The predefined speed of the roller shaft at which the electric motor is turned off can vary and is preferably selected as a function of the instantaneous position of the roller shutter, etc.
After the motor has been turned off because its speed has fallen below the predefined speed of the roller shaft, or because the predefined torque of the electric motor has been exceeded, or because the predefined change in torque of the electric motor has been exceeded, the direction in which the electric motor was rotating immediately prior to the shut-off is blocked. This is an effective way of preventing the motor from continuing to turn in the blocked direction after it has been turned on again.
In a further elaboration of the invention, a limited amount of play is built in between the roller shaft and a drive shaft driven directly by the drive. Because of this play, the drive shaft can continue to rotate by the amount of this play after the roller shaft has stopped turning. The continued rotation of this drive shaft by the amount of
Walddoerfer Dieter
Wolfer Hermann
Elero Antriebs- Und Sonnenschutz-Technik GmbH
Renz, Jr. , PC Eugene E.
Salata Jonathan
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