Screw device for the automated execution of a screwing operation

Description

[0001] The invention relates to a screwing device for the automated execution of a screwing process in which a screw is screwed to a screwing partner, in particular a workpiece, in the axial direction. Screwing devices for the automated execution of screwing processes typically have a feed unit for an infeed movement in the axial direction. Furthermore, such screwing devices comprise a rotary unit for generating a rotational movement. In conventional screwing devices, the feed unit is driven by compressed air. Due to the principle, this leads to certain limitations. Recent developments aim to replace compressed air drives with electric drives.

[0002] Based on this, the invention is based on the object of optimizing automated screwing processes.

[0003] US Pat. No. 5,549,169 A discloses a screwing device according to the preamble of claim 1, which comprises an electric motor-driven feed unit and a rotating unit. A screwing process is controlled in a position-dependent and force-dependent manner to enable the screw to be screwed into a thread as quickly as possible, in particular without damaging the thread.

[0004] Further position- and / or force-dependent controlled screw devices can be found, for example, in JP 2012 157 005 A, DE 10 2014 208 994 A1, JP 2010 264 514 A, US 2011 / 185 864 A1 and US 2008 / 314 162 A1.

[0005] The object is achieved according to the invention by a screwing device for the automated execution of a screwing process with the features of claim 1. Preferred developments are contained in the dependent claims.

[0006] The screwing device is in particular a device which is designed for mounting on an adjustment mechanism, especially for mounting on a robot hand of a particularly multi-axis (industrial) robot or on a multi-axis adjustment system along linear axes.

[0007] The screwing device comprises a feed unit for generating an axial feed movement across a stroke range. The feed unit has an electric feed motor for this purpose and is designed to detect instantaneous feed values, namely, to detect an instantaneous feed force, an instantaneous feed speed, and an instantaneous axial position of a feed part that is displaced in the axial direction. This is, in particular, a slide of the feed unit.

[0008] The screwing device further comprises a rotating unit for generating a rotational movement using an electric drive motor, wherein the rotating unit is designed to detect instantaneous rotational values, namely an instantaneous speed, an instantaneous torque, and an instantaneous angle of rotation. The screwing device further comprises a tool head designed to guide the screw during the screwing process.

[0009] In this case, the screwing process is understood to be a complete cycle from picking up the screw in an initial position to screwing the screw into the screw partner and then returning to the initial position. This screwing process is carried out by the feed unit in combination with the rotating unit. The screwing process consists of a feed component, in which a linear axial movement is carried out with the help of the feed unit, and a rotating component, in which a rotary movement is carried out with the help of the rotating unit. Part of the screwing process is the actual screwing process, in which the screw is screwed into or out of the screw partner. The screwing process is also referred to below as the screwing-in process. During this screwing process, both a rotary movement with the rotating unit and a feed with the feed unit regularly occur.

[0010] Before the actual screwing process begins, the screwing tool regularly advances toward the screwing partner using the feed unit. The feed portion of the screwing process therefore includes an infeed portion during which the screw is not yet in engagement with the screwing partner and during which, preferably, no rotational movement occurs. Engagement with the screwing partner is understood to be the beginning of the actual screwing process. The actual screwing process begins when the following conditions are met: a) A screwing tool, also called a bit or blade, is in (correct) engagement with a tool holder of the screw head; b) The screw sits on the screw partner; c) The screw is turned.

[0011] The infeed portion defines the part of the screwing process up to the start of the actual screwing process, or in the negative direction during a return stroke after the screwing process. The end of the infeed portion is reached when the three conditions mentioned above are met. During a return stroke, the beginning of the infeed portion is reached when at least one of these three conditions is no longer met.

[0012] Furthermore, a feed unit is arranged, which is designed to feed the respective screw to the tool head. This feed unit is typically mounted in a front area of ​​the screwing device and generally serves to pick up a screw at the beginning of the screwing process, i.e., the screwing cycle.

[0013] The feed unit is designed, for example, as a feed or injection channel, through which the screws are pushed into a ready position, for example by means of compressed air. Alternatively, the feed unit is designed in the manner of a gripper, for example as a mechanical gripper or as a vacuum gripper, particularly designed as a vacuum sleeve. The respective screw is gripped by means of the gripper from a ready position, for example a magazine. The feed unit of the screwing device is typically part of a feed system, which, depending on the design, has, for example, a storage container for the screws, a magazine, a vacuum system, a compressed air system, a injection hose, etc.

[0014] Furthermore, the device, at least during operation, comprises a screwing tool designed to grip a screw head, in particular to engage the screw head of the screw. The screwing tool can be an internal edge tool or an external edge tool. The screwing tool is rotatable by means of the rotary unit and displaceable in the axial direction, in particular relative to the tool head, by means of the feed unit.

[0015] The screwdriving device further comprises a control device for controlling the screwdriving process. The control device is designed such that the feed component of the screwdriving process is controlled based on the current feed force, in particular depending on the position. In particular, the infeed component, in which a pure infeed movement occurs without a superimposed rotary movement, is controlled based on the current feed force and specifically depending on the current position. The current feed force is therefore recorded, in particular depending on the current axial position, and the feed component of the screwdriving process, and thus also the control of the feed unit and / or the rotary unit, is also or partially exclusively based on this current feed force. Preferably, the feed unit and / or the rotary unit is also controlled based on the current feed force during the infeed component.

[0016] Alternatively or in addition to the control based on the current feed force, a common, coordinated control system for at least two of the three units (feed unit, rotation unit, feed unit) is implemented. For this purpose, one unit is controlled interactively depending on the current status values ​​of the other units.

[0017] According to a first variant, the control of the rotary unit and / or the feed unit is dependent on the current axial position of the feed unit. Alternatively or additionally, the control of the rotary unit is dependent on the current feed force of the feed unit. Furthermore, additionally or alternatively, the control of the feed unit is dependent on the current measured values ​​(status values) of the rotary unit.

[0018] Alternatively or in combination, the control of one or more of the units (feed unit, turning unit, infeed unit) is carried out depending on completed process steps. Each screwing process is formed by a cycle, which can generally be subdivided into a sequence of several process steps. These include, in particular: Feeding the screw into a ready position in the tool head with the help of the feed unit. If necessary, positioning the screwing device to the component by means of an adjustment mechanism to which the screwing device is attached, e.g. a robot or a multi-axis linear adjustment system. Feeding the screwing tool from a starting position until it engages with the screw head (part of the feed portion). If necessary, further feeding of the screw to the workpiece by means of feed of the feed unit (part of the feed portion). Screwing the screw into the workpiece (screwing process). Return stroke of the feed unit, in particular to the starting position (part of the (negative) feed portion).

[0019] The process step of screwing in the screw (actual screwing process) is typically subdivided into several sub-steps, namely the start of screwing in, possibly with thread cutting, further screwing in and final tightening (tightening) of the screw.

[0020] This screwing process, the actual screwing process, is controlled in a conventional manner, for example torque-controlled.

[0021] This control concept is generally based on the realization that with an electric feed drive, the current axial position information is typically available precisely and immediately, especially in combination with other current status values, so that the current status of the screwdriving process can be determined very precisely. Based on this, a defined and targeted control is derived depending on the current values ​​of the rotary unit and / or the feed unit. In contrast, precise, reliable current position information is not available with pneumatic drives, especially in combination with other current status values, for example, feed rate and position.

[0022] Preferably, the feed force is continuously monitored throughout the entire screwing process and, in particular, recorded and evaluated depending on the current feed position. In a preferred embodiment, both the current feed force and the current axial position of the feed part to be adjusted in the axial direction are continuously recorded over the entire stroke range of the feed unit. The stroke range of the feed unit is therefore composed of the stroke component for the feed portion and the stroke component during the actual screwing / screwing process.

[0023] Based on this combined information, namely position and feed force, the control system also preferentially detects errors during the screwing process, for example the following errors are detected: Missing or defective parts, especially workpiece and / or screw, existing interfering contours e.g. of objects, collision with an object.

[0024] All of these sources of error are preferably detected during the feed phase, i.e. before the actual screwing process.

[0025] This error detection results from the position-dependent evaluation of the feed force. If the feed force increases at an unexpected position, this could be due to an interfering contour or a collision, for example, or if the screw is faulty, e.g., too long, too stiff, etc. Stiffness is detected during the actual screwing process. If, contrary to expectations, there is no increase in the feed force, this could indicate, for example, a missing part. If an error is identified, the control system intervenes in the control of the feed unit and / or the rotary unit, particularly depending on the feed force and / or the axial position.

[0026] In a preferred embodiment, the control device can be parameterized for different types of screwing processes, i.e. can be freely adjusted by the operator. Different types of screwing processes here means that the screwing processes differ with regard to the screwing partners (workpiece and / or screw) and / or that the screwing processes differ with regard to the screwing parameters. Screwing parameters include, for example, the rotational speed during the screwing process, a tightening torque, etc. An individual speed profile is specified for the (total) stroke range for a respective type of screwing process, which has different speeds for the feed movement for different stroke sections. The feed unit is controlled according to the individual speed profile. At the same time, the current feed force is recorded and monitored depending on the position.In this context, monitoring is usually understood to include limiting the feed force. Alternatively or additionally, in the event of a deviation from a specified setpoint, the system is adjusted to the setpoint.

[0027] In general, defined position-dependent switchover positions are controlled in a targeted and rapid manner with a high level of process reliability, so that short cycle times are achieved. Switchover positions are understood in particular to be those (axial) positions in which a switchover of the screwdriving parameters takes place, such as a change of the feed values, the rotation values ​​or the parameters for the feed unit. In particular, a switchover position is understood to be a switchover in which a switching signal for one of the two other units is issued when a defined axial position of the feed unit is reached. The accompanying monitoring of the current feed force defines the switchover point and the switchover position is reliably detected. In this way, for example, the screwdriving tool can be moved quickly from an initial position towards an intermediate position (axial position) in which engagement with the screw head takes place.Shortly before reaching the target position, the feed rate switches from a high to a low feed rate, and then the correct engagement is recorded based on the feed force (expected increase). If the engagement is correct, a defined switchover position is present. This intermediate position is also, in particular, an intermediate position within the infeed portion, i.e., after reaching the intermediate position and engaging the screwing tool, a further axial infeed movement with the feed unit occurs before the screw reaches the screwing partner and the actual screwing process with screwing in begins.

[0028] Alternatively, this intermediate position is also a position in which the screw is already sitting on the screw partner.

[0029] After the screwing tool has engaged correctly, the rotation of the screwing tool is started.

[0030] In general, for example, the system first moves to an intermediate position under position control, then the feed rate is switched over (in particular reduced) while simultaneously activating the force monitoring system, and then the system switches over to a subsequent process step, for example starting the rotary drive.

[0031] If the feed force exceeds or falls below specified limits, switching points are preferably defined at which the feed rate and / or the rotational speed or the direction of these movements are changed. Preferably, certain actions are triggered depending on the position, such as one or more of the following actions: the start of the rotary movement of the rotary drive for screwing in, further rotation of the screwing tool by a certain value, slight resetting of the feed unit with subsequent forward stroke, etc. The particular advantage is that switching positions can be approached quickly and with high precision.

[0032] Specifically, the rotary unit is controlled based on the detected instantaneous feed force and the current position. The detected feed force therefore defines a switching point for the rotary drive.

[0033] Preferably, several axial positions are approached at different feed rates while simultaneously monitoring the feed force. Depending on the current axial position and the current feed force, several switching points are defined, depending on which changes are made in the control of the feed unit and / or the rotary unit.

[0034] For example, in underground applications where the screw is fed from below, it is necessary to secure the screw against falling back. For this purpose, the feed unit preferably moves to an intermediate position and executes a so-called locking stroke. In the intermediate position, the feed unit, in particular the screwing tool, prevents the screw from falling back, for example, by closing the opening of a feed channel with the screwing tool. Subsequently or previously, additional axial positions can be approached at which specific switching points are defined.

[0035] The particular advantage here is that several axial positions are defined within the entire stroke, and preferably also within the feed portion, which are approached at different speeds. This enables and provides for highly precise and rapid approach to any number of positions within the entire stroke, particularly with simultaneous force monitoring. Specifically, at least two, preferably more than two, more preferably more than three or more than four different axial positions are approached at different speeds.

[0036] Compared to a conventional pneumatic drive, this offers a number of advantages. A key process step in the screwdriving process is the reliable gripping (engaging or re-gripping) of the screw head by the screwdriving tool. With a conventional pneumatic drive, a damper is often required to slow the feed movement when the tool hits the screw. Such a damper is neither provided nor required for this purpose. Instead, the precise axial position is precisely specified and maintained by the electric feed drive.

[0037] The previously described switching positions and switching points preferably relate to process steps of the screwing process outside of the actual screwing of the screw into the screw partner, in particular these switching positions relate to special axial positions within the feed portion and thus within a stroke movement of the feed unit before screwing in or after screwing the screw into the screw partner.

[0038] Until now, it was not possible to ensure correct engagement of the screwing tool with the screw head right from the start of the screwing-in process without complex sensor technology. The force monitoring provided according to the invention when approaching the exact, predefined engagement position now achieves defined monitoring of whether the tool is correctly engaged with the screw head. Incorrect engagement occurs, for example, when the screw head and the tool are arranged in an incorrect relative rotational position to one another. The screw is preferably held at a predetermined axial position, for example by holding elements in the tool head. The control system therefore knows up to which axial position the tool can / must move in order to be in correct engagement with the screw head.Once this position is reached, the screwdriving tool, especially with an internal thread tool, rests at a defined axial engagement position inside the screw head. Until the axial engagement position is reached, there is generally no significant increase in force. In the case of improper engagement, this can be detected, for example, by an early increase in force. In such a case, special measures are taken, as explained in more detail below.

[0039] This measure ensures, in particular, that the tool engages the screw head without wear. In previous screwdriving processes, correct engagement often only occurs at the start of the screwdriving process, during which a high axial feed force is generally exerted on the screw. If the screwdriving tool is not already in correct engagement, this leads to relative rotation between the tool and the screw head. The measure described here therefore prevents abrasion on the tool and / or in particular on the screw head. Such abrasion can lead to contamination of the components and impair their function. This is particularly important for electronic components such as circuit boards. In the case of visible screws in particular, this also reliably prevents any visual impairment of the screw head.

[0040] According to a preferred embodiment, the feed unit comprises a feed channel, for example a firing channel and a hose, via which a respective screw is conveyed into the ready position with the aid of compressed air.

[0041] The control device is designed in such a way that after a respective screw has been fed into the ready position - in particular by compressed air - the feed unit moves to an intermediate position in which the screwdriving tool grips the screw head and remains in this intermediate position until a release signal is given. In this intermediate position, the screwdriving tool is already correctly engaged in the screw head, as previously described. This measure ensures that the screwdriving tool is already in the correct engagement when the subsequent screwing in of the screw begins, when the rotational movement is started. With conventional drives, there was a risk that the correct engagement was not achieved or was only achieved during the screwing process. This often led to a certain amount of abrasion, which is detrimental to the entire screwdriving process and in particular to contamination and / orcould lead to wear and tear.

[0042] Alternatively or in addition to the correct engagement of the screwing tool in the intermediate position, the compressed air supply is interrupted once the intermediate position is reached. This means that the compressed air supply is controlled depending on the axial position of the feed unit. This allows the required amount of compressed air or, in general, an operating gas to be reduced. The screw can be parked in the intermediate position until the release signal, for example, for the process step of screwing it into the workpiece. During this period, no compressed air is consumed.

[0043] Preferably, the screwing device is designed such that, upon reaching the intermediate position, the respective screw is prevented from falling back from the ready position, for example, into a hose opening. For this purpose, the screw is held in the intermediate position, for example, by mechanical clamping jaws.

[0044] In a preferred embodiment, it is provided that the screwing tool in the intermediate position blocks an opening point of the feed channel, ie the tool is located in front of an opening point as long as the tool is in this intermediate position.

[0045] As explained above, the invention uses the instantaneous feed force and the instantaneous axial position to check whether the screwing tool is in correct engagement with the screw head.

[0046] According to a preferred embodiment, the control device is preferably parameterizable such that individual force profiles can be specified for different types of screwdriving processes, with different feed forces being specified and defined within the respective individual force profile for different stroke sections. The feed is controlled based on the stored individual force profile. In this case, the current feed rate and, in particular, its direction are recorded and monitored, for example, limited or regulated to a setpoint, depending on the position.

[0047] The instantaneous feed force is generally actively measured using a measuring unit, such as a load cell. Alternatively, the instantaneous feed force is determined by evaluating parameters of the electric feed motor, specifically by evaluating the instantaneous motor current.

[0048] The advantage of this force control is that a defined force curve is specified and monitored across the entire stroke. Unlike conventional compressed air systems, in which the feed force is primarily determined by spring elements or the operating pressure of compressed air cylinders, this allows for an individually parameterizable force curve across the stroke range.

[0049] In a preferred embodiment, the influence of gravity is particularly taken into account or compensated for with a given force profile. This is also specifically provided for the different force profiles for different screwdriving processes. For this purpose, the feed direction and thus the orientation of the screwdriving tool with respect to the direction of the gravitational force are taken into account. The orientation of the feed movement is therefore specifically determined. Depending on this direction of movement (in the direction of the gravitational force, against the gravitational force, at an angle with respect to the gravitational force), different specifications for the feed force that must be applied by the feed unit are defined and set.

[0050] The orientation of the screwdriving device in space, and thus the direction of the feed force, is stored for each screwdriving process in a higher-level control system, such as a robot controller. Alternatively, this orientation is determined by a measuring unit during the screwdriving process, and a force profile specified for a defined stroke section is adapted. The specified force profile characterizes the desired force profile for a process step, such as screwing in or feeding in. If, for example, several screws with different orientations are screwed into a complex workpiece, such as an automotive component, the force profile for each screw is adapted depending on its orientation.

[0051] By specifying different feed forces for different stroke sections, the overall quality of the screwdriving process is improved. For example, in the case of a thread-forming screw, a high feed force is applied at the beginning of the screwdriving process during thread cutting. After the thread cutting process is completed, the feed force switches to a lower one during screwing in, before switching back to a higher feed force during the final tightening.

[0052] In addition to one or more force profiles for screwing in the screw, a force profile for unscrewing the screw is preferably also stored. Here, the return stroke is controlled according to the specified force profile. This means that the backward movement is controlled depending on the current force acting on the feed unit (negative feed force). When the screw is unscrewed, it is automatically moved backwards against the axial direction due to the thread. In this process, the screw exerts a certain force on the screwdriving tool. The return stroke is now controlled such that this force remains within a specified force window. This ensures that reliable engagement of the screwdriving tool is maintained during the return stroke.

[0053] For the previously described consideration of the gravitational force, the mass of the screwdriving device, specifically the mass of the parts moved by the feed unit, is generally taken into account. In a preferred embodiment, the control device is further configured such that a mass for an add-on component can be input, and that a current orientation of the tool head can be detected. This mass of the add-on component is taken into account for the specified force profile, taking into account the orientation. This force profile is then adjusted accordingly. The add-on component could be, for example, the (replaceable) screwdriving tool.

[0054] This design is based on the consideration that special add-on components are often used by the customer, i.e. components that do not originate from the manufacturer of the screwdriving device, or that a specific screwdriving device can be individually configured using such add-on elements. These add-on components have a significant influence on the forces that occur during the screwdriving process. The control device is now designed in such a way that such different add-on components can be taken into account by entering the mass. The control device can therefore also be freely configured by the end user with regard to the mass. The stored force profiles are therefore adapted for a specific component based on the entered mass. The current orientation is in turn either measured using a measuring unit or derived from a higher-level control system.

[0055] In individual cases, the screwdriving device comprises several rotary units and several feed units, with the stroke movements of the feed units being synchronized with each other. When using multiple rotary units, the feed movements of the feed units are specifically coordinated. Coordination is performed, in particular, via a higher-level control device. The two feed units, for example, are therefore synchronized, particularly depending on the travel. This design has the particular advantage of enabling the simultaneous tightening of several screws, thus ensuring uniform tightening.Such a synchronized feed movement is used, for example, to connect two components, especially two half clamps, since in this case the controlled feed ensures that no additional transverse forces are applied to the screws, so that the two components are screwed together evenly and parallel.

[0056] In a useful further development, each screwing process takes place within a (working) cycle, in which the feed unit, the feed unit and the rotating unit each cyclically carry out several process steps. Each of these units therefore carries out an individual process cycle, typically with several process steps. For example, the rotary movement of the rotating unit, the feed movement of the feed unit and the feeding via the feed unit are typically divided into different steps during the screwing process. These individual process steps of the rotating unit and / or the feed unit are controlled by the control device depending on the current axial position and / or the current feed force of the feed unit. The control device can be, for example, a higher-level control device, which coordinates and synchronizes the individual process cycles of these different units.There is therefore an interaction between the individual processes of the feeding unit, the feed unit and the turning unit.

[0057] Previously, specific process steps were typically triggered via a timer. For example, the rotary unit was triggered by the higher-level control system to execute a rotary movement after a certain time, after the feed unit had received a corresponding control signal. This time-controlled triggering is now being replaced by event-driven triggering. This enables a shorter cycle time for the screwdriving process and also reduces the susceptibility to failure.

[0058] For example, a process gas, such as compressed air for shooting in the screws or a vacuum for a vacuum sleeve that may be used, is switched on and / or off depending on the current position of the feed unit.

[0059] Another example is the correct engagement of the screwing tool with the screw head. Once the correct engagement position is reached, the rotary drive is controlled appropriately.

[0060] To reliably locate a correct engagement, the following procedure is preferred: First, the screw driver is advanced in the axial direction, initially at a fixed rotational position (the screw driver is not rotating). Alternatively, the screw driver rotates during the advance movement, particularly at a low rotational speed.

[0061] Based on the current position and feed force data, a check is made to determine whether the engagement is correct. If the engagement is incorrect, the rotary drive and / or feed unit is controlled differently. Specifically, especially in the variant with the fixed rotational position of the screwdriving tool, a slight return stroke and / or slight further rotation of the rotary drive by a defined angle of rotation, for example 15°, 30°, or 45°, is provided before a new feed is initiated. This is accompanied by monitoring of the position and feed force until the engagement is correct. This process is repeated as necessary until the screwdriving tool is reliably in correct engagement with the screw head.

[0062] Specifically in the second variant, with the rotation of the screwdriving tool during the feed movement, if an increased feed force is detected at a feed position before the correct engagement, thus indicating an incorrect engagement, the screwdriving tool continues to rotate at a defined (limited) feed force until the correct rotational position for the correct engagement is reached, so that the screwdriving tool then fully engages the tool holder. In this variant, a feed force limitation is activated, preferably when an incorrect engagement is detected, or possibly also depending on an axial position before impacting the screw, to prevent damage to the screw head during the relative rotation until the correct rotational position is reached.

[0063] Correct engagement is detected if the feed force does not exceed a certain limit up to a defined axial position (which corresponds to the position at which the screwdriving tool is fully inserted into the tool holder). Incorrect engagement is detected if an increase in the feed force is detected before this defined axial position, particularly in an area corresponding to the depth of the screw's tool holder.

[0064] According to a preferred embodiment, the control device is further designed to detect wear of the feed unit. For this purpose, the forces occurring are recorded and evaluated during a cyclically recurring lifting movement with constant boundary conditions. The forces occurring during (positive or negative) feed are determined under the same conditions, so that only the factors relating to the feed are taken into account for the forces occurring. These forces are either feed forces or, more specifically, return stroke forces, i.e. in particular the forces required to return the feed unit to its starting position. A return stroke to an initial position is specifically used for the cyclically recurring lifting movement. During this return stroke, only forces occur that are assigned to the feed unit as such and that are independent of the forces when screwing in the screw.Based on varying forces during the return stroke, it is possible to determine wear, for example stiffness, contamination, etc.

[0065] According to a preferred development, the instantaneous feed rate and the instantaneous rotational speed are synchronized with one another in such a way that the feed corresponds to an axial movement resulting from a predetermined pitch of the thread of the screw and the instantaneous rotational speed.

[0066] This design is based on the consideration that in special applications a force-controlled feed can lead to damage, for example to the workpiece. This applies particularly to soft materials or multi-layer materials where the individual layers have different hardnesses. If, for example, the screwdriving process is carried out in a force-controlled manner or with a predetermined feed force on a very soft material such as a spongy fabric, there is often a risk that the thread of the screw will be pushed through the soft material and no screwing process will take place. This applies in particular to thread-cutting screws. The measure proposed here ensures that the feed is exactly correlated with the thread pitch at the current rotational speed. In this respect, the rotary drive and feed unit operate synchronously.The required thread pitch, which is then reflected in the thread cut into the material of the workpiece, is therefore maintained regardless of the material properties.

[0067] Embodiments of the invention are explained in more detail below with reference to the figures. Fig. 1 a side view of a screwing device, Fig. 2 to 4 each a partial sectional view of a screwing device in the area of ​​a tool head with a feed unit in different working positions.

[0068] One in the Figure 1 The screwing device 2 shown as an example serves to automatically carry out a screwing process in which a screw 4 (cf. Fig. 2 to 4) is screwed into a screw partner. The screw partner is, in particular, a workpiece, for example, a component for a motor vehicle. Preferably, the screw 4 is a thread-forming screw 4, which forms the thread itself when screwed into the workpiece. Alternatively, the screw partner has a prefabricated thread into which the screw is screwed.

[0069] The screwing device 2 has a feed unit 12 with an electric feed drive 14a for the feed movement. Furthermore, the screwing device has a rotary unit 15 with a further electric drive 14b. A screwing tool 16 is set in a rotary movement during the screwing process via the rotary unit. In addition, the screwing tool is moved in and counter to an axial direction 18 in a controlled manner by means of the feed unit 12. The screwing tool 16 is, in particular, a rod-shaped element that carries a rotation transmission element, such as a screwdriver bit or a socket wrench, at its front end. The rotation transmission element or the entire screwing tool 16 is designed to be replaceable.

[0070] The feed unit 12 has a movable feed carriage 12a and a stationary part 12b. During operation, the stationary part 12b is attached, for example, to a tool carrier or a robot hand of an adjustment mechanism, such as an industrial robot. The automated screwing process is, in particular, a fully automated screwing process. In this process, the adjustment mechanism with the screwing device mounted on it moves to a desired position. The actual screwing process is then performed at this position.

[0071] In the illustrated embodiment, the fixed part 12b is arranged laterally next to the rotary unit 15. The rotary unit 15 is attached to the feed carriage 12a and moves with it in and against the axial direction 18.

[0072] A tool head 22 is attached to the front end of the stationary part 12b, in particular to a bent fastening flange. In the exemplary embodiment, this has a feed unit 24 for feeding the screws 4 into a ready position. In the ready position, the screw is located within a sleeve-shaped holding element 26 (see also Fig. 2 to 4 ). This preferably has retaining claws at its front end, which hold the screw 4 in a defined readiness position. The retaining claws can be opened radially against an elastic, radial clamping force, so that the screw can pass through the retaining element 26 during the screwing process.

[0073] The screwing device 2 shown is either designed as a stationary system to which the components to be screwed are fed. However, the screwing device 2 is preferably designed as a movable screwing device 2 and is attached, for example, to a robot with which it is moved to a desired position.

[0074] The screwing process is fully automated, without requiring any user interaction, such as manually guiding the screwing device 2 or starting a respective individual screwing process. The screwing device 2 and the screwing process are controlled by means of a control device 28. This typically has several functions that are implemented in different, even spatially separate, control units or in a common control unit. These control functions include, in particular, the control of the rotational movement of the screwing tool 16 via the rotary unit 15, the feed movement of the screwing tool 16 via the feed unit 12, the feeding of the screws 4 via the feed unit 24, and the control of the entire process as a higher-level control function.

[0075] Typically, the individual units 12, 15, 24 each have specific controllers that control individual functions of the units 12, 15, 24. These include, for example, motor controllers for the electric drives 14a, 14b. The drives 14a, 14b are electric motors, in particular rotary motors or linear motors. If necessary, gear elements can be provided to generate the desired rotary or feed motion.

[0076] In the present case, these individual controls together form the entire control device 28. In addition to these individual controls, the control device also has a higher-level control unit, which is integrated, for example, in a machine control system for the entire system.

[0077] During a screwing process, the rotary unit 15 continuously records instantaneous rotational values, namely at least an instantaneous speed, an instantaneous torque, and an instantaneous angle of rotation. The feed unit 12 also continuously records instantaneous feed values ​​during the screwing process, namely an instantaneous feed force, an instantaneous feed rate, and an instantaneous axial position of the feed carriage 12a.

[0078] The individual, currently recorded state values, in particular the current rotation values ​​and the current feed values, are either measured using measuring elements or determined indirectly, e.g., by evaluating the current motor characteristics of the electric drive motors 14a, 14b. These state values ​​are transmitted via data to the control device 28, where they are processed to control the screwing process.

[0079] During the screwing process, the screwing is controlled depending on the axial position of the feed slide 12a and thus depending on the axial position of the screwing tool 16 and depending on the current, position-dependent feed force.

[0080] Alternatively or additionally, a common coordinated control takes place between the rotary unit 15 and the feed unit 12 and / or a coordinated control takes place between the feed unit 24 and the feed unit 12. Thus, an interactive control takes place between at least two of these units, wherein the higher-level control unit of the control device 28 controls one unit depending on the current state values ​​of the other unit, as previously described in the general description section.

[0081] By providing electric drives 14a, 14b, special control processes are enabled and implemented, which lead to improved control of the screwing process.

[0082] An example of an interactive control of the feed unit 24 depending on the current axial position of the screwing tool 16 is exemplified in connection with the Figures 2-4 explained in more detail. The feed unit 24, which is only partially shown, has a feed channel 30, which is oriented at an angle oblique to the axial direction 18. A respective screw 4 is fed via this feed channel 30 with the aid of compressed air into a ready position. This ready position is, for example, the one shown in Fig. 2 shown position, but prefers the one in Fig. 3The position shown is in which the screw 4 rests against the front end region of the holding element 26 and is held by it. For this purpose, a hose is typically connected to the feed channel 30, through which the screws 4 are fed. In this ready position, the screw 4 is located within the tool head 22.

[0083] After the screw 4 has been inserted, a control signal is sent to the feed unit 12 so that the screwing tool 16 is moved in the axial direction 18 into an intermediate position, as for example in the Figure 2 In this intermediate position, the screwing tool 16 blocks an opening 32 of the feed channel 30 and thus prevents the screw 4 from falling back into the feed channel 30. This is necessary, for example, in underground applications. The Figures 3 and 4 The positions of the screwing tool 16 shown define intermediate positions in which the mouth opening 32 is blocked

[0084] As soon as the screwing tool 16 has reached the intermediate position, a control signal is sent to the supply unit 24, whereupon the compressed air supply is interrupted, ie a compressed air supply is switched off so that no compressed air is consumed.

[0085] Based on the Figures 3 and 4 the process step of "finding the correct engagement" of the screwing tool 16 in the screw head 34 is explained: For this purpose, the screwing tool 16 moves forward in the axial direction 18, whereby the feed force is monitored as a function of the axial position during this process.

[0086] If the screw 4 is not already in the position indicated in the Figures 3 and 4 shown, it is moved forward by the screwing tool 16. The readiness position is a known, defined axial position, as shown in the Figure 3is shown. The screwing tool 16 moves forward and engages the screw 4; in particular, the screwing tool 16 plunges a head (polygon wrench) into the screw head 34. This position represents a (possibly further) intermediate position in which the correct engagement of the screwing tool 16 occurs before the actual screwing process begins with the screwing of the screw 4 into the workpiece.

[0087] Preferably, a release signal to start the actual screwing in and thus to start the screwing in is only given when correct engagement is ensured.

[0088] In the position according to the Figure 3The screwing tool 16 is not yet fully engaged with the screw 4. This is detected because the force increases too early, i.e., not within a position window for proper engagement. This is due, for example, to the screwing tool 16 and the screw head 34 being rotated relative to each other, so that the screwing tool 16 cannot penetrate into the screw head 34 to the intended, defined axial position.

[0089] In such an error case, the control device 28 detects a non-correct condition and takes measures to ensure proper engagement. Various strategies are possible for this. For example, a slight return stroke and / or a rotation of the screwing tool 16 by a few degrees is performed, followed by a renewed advance. As soon as the correct rotational position is reached, the screwing tool 16 plunges into the screw head 34 until a bottom of the receptacle of the screw head 34 is reached and a force increase occurs. This situation is Figure 4 indicated. The control device 28 now detects that the force increase occurs at the defined axial position. Next, for example, an enable signal for the rotary drive 15 is issued. List of reference symbols

[0090] 2Screwing device. 4Screw 12Feed unit 12aFeed carriage 12bFixed part 14aElectric feed drive for feed movement 14bElectric drive for rotation movement 15Rotary unit 16Screwing tool 18Axial direction 20Rotary drive 22Tool head 24Feed unit 26Holding element 28Control device 30Feed channel 32Mouth opening 34Screw head

Claims

1. Screwing device for carrying out a screw-driving procedure in an automated manner, in which procedure a screw is screwed to a threaded partner in an axial direction, wherein the screwing device has - an advancing unit for generating an axial advancing movement over a stroke range, wherein the advancing unit has an electric advancing motor and is designed for detecting momentary advancing values, specifically a momentary advancing force, a momentary advancing rate, and a momentary axial position; - a rotating unit having an electric drive motor for generating a rotating movement, wherein the rotating unit is designed for detecting momentary rotational values, specifically for detecting a momentary rotating speed, a momentary torque and a momentary rotational angle; - a tool head for guiding the screw; - a feeding unit for feeding the screw into a standby position; - a screw-driving tool which is designed for gripping a screw head of the screw and which is rotatable by means of the rotating unit and displaceable in the axial direction by means of the advancing unit; - a control device for controlling the screw-driving procedure, wherein controlling an advancing fraction of the screw-driving procedure takes place by means of a momentary advancing force, characterized in that the control device is designed in such a manner that the momentary advancing force and the momentary axial position are used to verify whether the screw-driving tool is correctly engaged with the screw head.

2. Screwing device according to the preceding claim, wherein common, coordinated controlling of the advancing unit is performed by the rotating unit and / or by the feeding unit, wherein to this end interactive controlling of the one unit takes place as a function of momentary state values of the other unit.

3. Screwing device according to any one of the preceding claims, wherein the control device is designed in such a manner that, during the entire advancing movement over the stroke range, the momentary advancing force is detected and evaluated as a function of the axial position.

4. Screwing device according to the preceding claim, wherein the control device is designed in such a manner that, as a function of the stroke-travel-dependent momentary advancing force, one or a plurality of the following errors is detected in particular during an advancing fraction prior to driving the screw into the threaded partner: - detection of a missing or faulty part, for example a screw or a workpiece; - detection of an interference contour of an object, or collision with an object.

5. Screwing device according to one of the preceding claims, wherein the control device is designed in such a manner that a plurality of axial positions are approached at different advancing rates while simultaneously monitoring the advancing force, wherein defined as a function of the momentary axial position and the momentary advancing force are different switching points, as a function of which variations in terms of the actuation of the advancing unit and / or the rotating unit are performed.

6. Screwing device according to one of the preceding claims, which has a feeding duct for feeding the screw with the aid of compressed air into a standby position, wherein the control device is designed in such a manner that, after feeding a respective screw into the standby position by compressed-air activation, the advancing unit moves to an intermediate position and remains there up to a release signal, whereby a supply of compressed air is interrupted upon reaching the intermediate position.

7. Screwing device according to one of the preceding claims, which has a feeding duct for feeding the screw into a standby position, wherein the control device is designed in such manner that, after providing a respective screw in the standby position, the advancing unit moves to an intermediate position in which the screw-driving tool grips the screw head and remains there up to a release signal.

8. Screwing device according to one of the preceding claims, wherein the control device is designed in such a manner that, as a function the direction of the advancing movement, the advancing force is compensated as a function of the effect of gravitation.

9. Screwing device according to one of the preceding claims, wherein the control device is designed for driving out a screw, wherein for this purpose a return stroke according to a predetermined force profile is actuated.

10. Screwing device according to one of the preceding claims, wherein the control device is designed in such a manner that a mass for an in particular interchangeable attachment component can be parameterized, and that a gravitational effect of the attachment component is taken into account in the force profile, wherein preferably a momentary orientation of the tool head is detectable and taken into account.

11. Screwing device according to one of the preceding claims, which comprises a plurality of rotating units and a plurality of advancing units, wherein the control device is designed in such a manner that the stroke movements of the advancing units are mutually synchronized.

12. Screwing device according to one of the preceding claims, wherein for carrying out a respective screwing operation within a cycle, the feeding unit, the advancing unit and the rotating unit each carry out individual process steps, wherein the individual process steps of the advancing unit and / or the rotating unit are actuated by the control device as a function of the momentary axial position and / or the momentary advancing force of the advancing unit.

13. Screwing device according to one of the preceding claims, wherein the control device is designed in such a manner that the following steps are carried out: a) moving the screw tool to the screw head; b) verifying the correct engagement by evaluating the momentary data pertaining to the position and the advancing force; c) in the event of incorrect engagement, modified actuation of the rotary drive and / or the advancing unit; d) further advancing and monitoring the position and the advancing force as to whether a correct engagement has been achieved; and e) repeating steps b) to d) as required.

14. Screwing device according to one of the preceding claims, wherein the control device is designed for detecting wear on the advancing unit, and for this purpose during a cyclically recurring stroke movement with constant parameters, in particular during a reverse stroke, detects and evaluates arising forces.

15. Screwing device according to one of the preceding claims, wherein the control device is designed in such a manner that the momentary advancing rate and the momentary rotation speed are synchronized, specifically in such a manner that the advancing by the advancing unit corresponds to an axial movement which results from a predefined pitch of the thread of the screw and the momentary rotating speed.