Pressing tool for pressing workpieces
A pressing tool for pressing workpieces is described. The pressing tool comprises a hydraulic pump for conveying a hydraulic fluid, an electric motor for driving the hydraulic pump, a working cylinder which is hydraulically connected to an outlet of the hydraulic pump, a pressure-relief valve which is hydraulically connected to the outlet of the hydraulic pump and which opens at a certain predefined pressure P v of the hydraulic fluid, an electronic control for controlling the electric motor and a sensor 60 which monitors the state of the pressure-relief valve and emits a signal which describes the state of the pressure-relief valve to the electronic control. Furthermore, a method of operating such a pressing tool is described.
1. A pressing tool for pressing workpieces, comprising:
a hydraulic pump for conveying a hydraulic fluid;
an electric motor for driving the hydraulic pump;
a working cylinder which is hydraulically connected to an outlet of the hydraulic pump;
a pressure-relief valve which is hydraulically connected to the outlet of the hydraulic pump and which opens at a certain predefined pressure (P v ) of the hydraulic fluid;
an electronic control for controlling the electric motor; and
a sensor which directly monitors a state of the pressure-relief valve, wherein the sensor determines a distance (L) between a movable part of the pressure-relief valve and a part that is fixed with respect to the pressing tool, and wherein the sensor emits a signal which describes the state of the pressure-relief valve to the electronic control.
2. The pressing tool according to claim 1 , wherein the pressure-relief valve comprises a movable valve piston which is preloaded against a valve seat by means of a spring.
3. The pressing tool according to claim 2 , wherein the valve piston comprises a permanent magnet.
4. The pressing tool according to claim 1 , wherein the sensor comprises a magnetic sensor which is influenced by a magnet at the pressure-relief valve.
5. The pressing tool according to claim 4 , wherein the magnetic sensor comprises a hall effect sensor.
6. The pressing tool according to claim 4 , wherein the magnetic sensor comprises a reed switch.
7. The pressing tool according to claim 4 , wherein the magnetic sensor comprises an inductive sensor.
8. The pressing tool according to claim 1 , wherein the sensor comprises an optical sensor.
9. The pressing tool according to claim 1 , wherein the sensor comprises an electric switch.
10. The pressing tool according to claim 1 , wherein the electric motor is a brushless DC motor.
11. A method of operating a pressing tool for pressing a workpiece, comprising:
driving a hydraulic pump by means of an electric motor;
conveying a hydraulic fluid by means of the hydraulic pump;
opening a pressure-relief valve which is hydraulically connected to an outlet of the hydraulic pump at a certain predefined pressure (P v ) of the hydraulic fluid;
directly monitoring a state of the pressure-relief valve by means of a sensor;
emitting a signal to an electronic control, wherein the signal describes the state of the pressure-relief valve; and
controlling the electric motor by means of the electronic control based on the signal; and
determining a distance (L) between a movable part of the pressure-relief valve and a part that is fixed with respect to the pressing tool by the sensor.
12. The method according to claim 11 , wherein the step of determining the distance (L) takes place:
in an optical manner, wherein the sensor comprises an optical sensor;
in a magnetic manner, wherein the sensor comprises a magnetic sensor;
in a magnetic manner, wherein the sensor comprises a hall effect sensor;
in a magnetic manner, wherein the sensor comprises a reed switch;
in an inductive manner, wherein the sensor comprises an inductive sensor;
in an electro-mechanical manner, wherein the sensor comprises an electric switch; and/or
in a capacitive manner, wherein the sensor comprises a capacitive sensor.
13. The method according to claim 11 , wherein the sensor is adapted to detect both a closed and an open state of the pressure-relief valve.
14. The method according to claim 11 , wherein the sensor is adapted to continuously detect the distance (L) between the movable part of the pressure-relief valve and the part that is fixed with respect to the pressing tool.