In automatic machine loading, it is not enough to simply bring the part accurately to the chuck, collet, or fixture. Even with a correctly programmed robot, there are still workpiece tolerances, minor positional deviations, backlash in the fixture, basing errors, and differences between the actual and calculated position of the part.
If a rigidly fixed gripper feeds the workpiece with misalignment, the load is transferred to the fingers, gripper body, rotary unit, and technological tooling. In the best case, the robot will not be able to install the part. In the worst case, an impact, jamming, finger damage, or an unplanned stop of the automated cell may occur.
For such tasks, a compensation module is used. It is installed between the rotary unit and the gripping unit, compensates for small deviations during part feeding, and reduces the risk of equipment damage caused by inaccurate positioning.
The KIPVALVE product range includes two main solutions:
- VCHT-ZG – a compensation module for VRTG series rotary units;
- VCHT-HE – a compensation module for VRTE series rotary units.
The choice depends not on the module name, but on the design of the rotary unit, the rotation angle, the type of grippers, and the equipment loading scenario.
Why a Compensation Module Is Needed
A compensation module helps the gripping unit adapt to small deviations when installing a part. It is especially useful when a robot or gantry feeds a workpiece into a limited space: a machine chuck, collet clamp, jig, mold, inspection device, or mounting fixture.
A compensation module may be required in the following cases:
- the part has dimensional or shape tolerances;
- the position of the workpiece in the tray changes from cycle to cycle;
- the part must be fed into a chuck or fixture with a limited entry clearance;
- the robot operates with long fingers or a large adapter plate;
- the part has an offset center of gravity;
- a rotary unit is used in the assembly;
- impact load during feeding must be reduced;
- there is a risk of misalignment during machine loading or unloading;
- part installation error control is required.
Compensation does not replace accurate robot setup, a rigid mounting plate, or correctly designed fingers. Its task is to work with small technological deviations, not to correct major layout errors.
What Deviations the Module Compensates For
A compensation module is used when the gripping unit must have a small degree of movement relative to the rigid axis of the robot or rotary unit.
It can compensate for:
- minor part displacement during gripping;
- workpiece deviation in a tray or on a conveyor;
- basing error in the fixture;
- minor misalignment when inserting the part into a chuck or collet;
- deviations caused by the tolerances of the part itself;
- skewing caused by finger length or workpiece geometry;
- a small difference between the calculated and actual position of the part.
The compensation module is most often used in CNC loading. The robot may hold the workpiece securely, but lateral force can occur when feeding it into the machine. Without compensation, the load is transferred to the part, fingers, and fixture. With the module, the unit can gently adapt to the actual position of the part.
VCHT-ZG and VCHT-HE: What Is the Difference?
VCHT-ZG for the VRTG Rotary Unit
VCHT-ZG is used together with VRTG series rotary units. These units are designed to work with two grippers and rotate the head by 180°. This configuration is in demand for automatic machine loading and unloading, when one gripper removes the machined part while the second one simultaneously prepares a new workpiece.
The VCHT-ZG compensation module helps reduce the risk of misalignment when installing a part into a technological position. It is suitable for tasks where cycle speed, feeding accuracy, and compact gripping unit layout are important.
For VRTG12, for example, a VGFR28-76 parallel gripper and a VGFZ34-68 centering gripper can be used. The choice of a specific combination depends on the part shape, gripping method, workpiece weight, and positioning requirements during feeding.
VCHT-HE for the VRTE Rotary Unit
VCHT-HE is used together with VRTE series rotary units. The VRTE series is designed for installing two grippers and rotating the working unit by 90°. This solution is used when the part must be reoriented between operations, fed into the fixture at a different angle, or when a more compact equipment loading cycle must be arranged.
HT-HE helps compensate for small deviations when working with VRTE and reduces the risk of impact load transfer to the gripping unit. For VRTE40, the website specifies compatibility with the VGFR36-96 two-finger parallel gripper, but the final configuration must be determined based on the part and fixture parameters.
Main Selection Rule
- if a VRTG rotary unit with 180° rotation is required, choose VCHT-ZG;
- if a VRTE rotary unit with 90° rotation is required, choose VCHT-HE.
An adapter flange is not required to connect the compensation module to the corresponding rotary unit: the modules are designed for installation as part of a compatible KIPVALVE assembly.
When a Compensation Module Is Really Needed
The module should be included in the project when, without it, the risk of part misalignment or impact load during feeding increases.
Typical situations include:
- loading round parts into a lathe chuck;
- installing bushings, flanges, and housings into a jig;
- feeding parts into a collet;
- working with long or heavy fingers;
- loading parts with shape tolerances;
- transferring a workpiece between machines;
- automatic assembly with precise insertion of one part into another;
- working with workpieces whose position in the tray may change;
- using a rotary unit in a high-frequency cycle.
It is especially important to assess the need for compensation when the working fingers have a large overhang. The farther the contact point with the part is from the gripper body, the higher the moment load and the greater the risk of misalignment during feeding.
When a Compensation Module Will Not Solve the Problem
Compensation should not be used as a way to hide a design error. The module will not correct the situation if:
- the gripper has been selected without sufficient force reserve;
- the fingers are too long or too heavy;
- the part is held only by friction on an oily surface;
- the working pressure is unstable;
- the center of gravity of the part is significantly offset;
- the rotary unit does not match the moment of inertia of the assembly;
- the fixture has excessive backlash;
- the robot is programmed with a major positioning error;
- the part physically does not fit into the technological position.
In these cases, the root cause must first be eliminated: recalculate the fingers, select a different gripper size, change the gripping method, modify the fixture, or adjust the robot trajectory.
Sensors and Installation Error Control
The compensation module can be used together with a KIPPRIBOR LA08 inductive sensor. This solution makes it possible to monitor the position of the compensation unit and transmit a signal to the control system in case of part deviation or a possible collision during installation.
This is especially useful in automatic lines, where it is important not just to complete the cycle, but to stop the equipment before the fixture or gripper is damaged.
The sensor does not replace the safety system, but it helps implement technological situation control:
- the part has not reached the required position;
- the workpiece has been installed with misalignment;
- resistance has occurred during insertion into the fixture;
- the gripping unit has deviated beyond the permissible limit;
- the cycle must be stopped and a message displayed to the operator.
How to Select a Compensation Module for a Robot
Before selecting the module, it is necessary to define the configuration of the entire system, not just the type of rotary unit.
For engineering verification, the following data is required:
- a drawing or 3D model of the part;
- workpiece weight;
- shape and dimensions of the gripping area;
- material and surface condition;
- gripper type: parallel, centering, or reinforced;
- length and weight of the working fingers;
- type of rotary unit;
- rotation angle;
- center of gravity position;
- cycle time;
- method of installing the part into the machine or fixture;
- need for a control sensor;
- operating conditions: temperature, dust, coolant, chips, vibration.
It is also necessary to consider the total weight of the entire assembly: grippers, fingers, adapter plates, sensors, the compensation module, and the part itself. When working with rotary units, not only weight is important, but also moment of inertia, overhang, and load on the buffer devices.
Machine Loading Unit Configuration
A typical system for automatic part feeding may include:
- an industrial robot, gantry, or manipulator;
- a VRTG or VRTE rotary unit;
- a VCHT-ZG or VCHT-HE compensation module;
- one or two pneumatic grippers;
- working fingers designed for the part geometry;
- position control sensors;
- pneumatic system components;
- a mounting plate and adapter elements.
This approach makes it possible to select not a separate module, but a working solution for a specific technological cycle.
Selecting VCHT-ZG or VCHT-HE for Your Task
A compensation module is needed where the part must enter the technological position without impact, misalignment, or excessive load on the gripping unit. HT-ZG is used for VRTG, and HT-HE is used for VRTE. However, the final choice depends on the entire system: the types of parts, fingers, grippers, rotary unit, cycle speed, and accuracy requirements.
Send us a drawing or 3D model of the part, machine parameters, and a description of the process. Our KIPVALVE specialists will help select a compensation module, rotary unit, pneumatic grippers, and position control sensors for your robotic cell.
Frequently Asked Questions
Can VCHT-ZG be installed on a VRTE rotary unit?
No. VCHT-ZG is intended for the VRTG series. HT-HE is used for VRTE rotary units.
Is a compensation module required for every robotic cell?
No. It is needed when small deviations, misalignment, or impact loads may occur during part feeding. With a stable fixture, accurate positioning, and sufficient rigidity margin, the need for compensation is determined by engineering calculation.
Can a compensation module hold a heavy part?
The module is not an independent gripper and does not replace the load capacity calculation of the pneumatic gripper, fingers, and rotary unit. For a heavy part, the entire system must be evaluated, including the center of gravity, moment of inertia, and gripping method.
What is the purpose of a sensor on the compensation module?
The sensor makes it possible to monitor unit deviation during part installation and transmit a signal to the control system in case of a potential feeding error or collision.
Publication date: