Electrohydraulic Pressing Motor Control via Current Drop
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for automatically switching off an electric motor in electro-hydraulic pressing tools are unreliable due to dependence on external factors such as battery charge, motor condition, and hydraulic fluid temperature, leading to inconsistent current drops and potential premature or missed switch-off events.
Innovation Solution
The method detects a drop in current when the pressure relief valve opens and switches off the electric motor only when the current drop meets a predetermined value or occurs over a specified time, independent of absolute current values, ensuring consistent and reliable motor shutdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If the electric motor is switched off based on absolute current values, then automatic switch-off can be achieved, but the reliability is poor due to dependence on external factors such as battery charge, motor condition, and hydraulic fluid temperature
Solution Approach 1:
The invention changes the control parameter from absolute current values to relative current drop values. Instead of monitoring whether current reaches a fixed threshold, the system monitors the change in current (ΔI) between the maximum current during pressing and the current at the end of pressing. This parameter transformation eliminates dependence on external factors like battery charge level, motor condition, and fluid temperature, as these factors affect both the maximum and end currents equally, thus their influence cancels out in the difference calculation.
2Extent of automation
If the electric motor is switched off based on current drop, then automatic control is achieved, but false triggers may occur from short-term current drops during the pressing process
Solution Approach 1:
The invention performs preliminary measurement of the maximum current (I_max) during the pressing process before the valve opens. This maximum current value is stored and used as a reference for subsequent comparison. By establishing this reference point in advance, the system can accurately distinguish between normal current fluctuations during pressing and the significant current drop that occurs when the pressure relief valve opens, thereby preventing false triggers.
Solution Approach 2:
The system continuously monitors the current during the pressing process and compares it with the previously stored maximum current value. When the current drops by a predetermined amount (ΔI) from the maximum, the system triggers the switch-off signal. This feedback mechanism ensures that only significant current drops (indicating valve opening) are detected, while minor fluctuations during pressing are ignored.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach ensures the electric motor is switched off reliably and consistently after the valve opens, reducing fluid delivery to the minimum necessary, avoiding false triggers from short-term current drops and ensuring the pressing process can be completed automatically without user intervention.
Implementation Method 1
fluid is pumped by a hydraulic pump driven by an electric motor in order to displace the piston
Implementation Method 2
the hydraulic cylinder has a valve, such as a pressure relief valve, which opens when a limit pressure is reached
Implementation Method 3
the current consumption of the electric motor is measured. When the pressure relief valve opens, the current drops
Data Source
Figure 1
Figure 2
AI summary
In the case of a method for automatically controlling an electrohydraulic pressing tool, in particular for producing pipe connections, to actuate the pressing tool a hydraulic piston (10) is moved, in that fluid is pumped into a hydraulic cylinder (12) by a hydraulic pump (14) driven by means of an electric motor (26). When a limiting pressure in the hydraulic cylinder (12) is reached, a pressure relief valve (32) opens, and so the hydraulic fluid can flow into a reservoir (16). With the aid of a control device (30), a current drop at the motor (26) is detected when the valve (32) opens. The electric motor (26) is switched off when the current falls by a predetermined value (?I) and/or decreases over a predetermined time period (?t) after reaching a limiting current.